CHAPTER XII

GASEOUS AND LIQUID FUELS

=Gaseous and Liquid Fuels.=--Gaseous and liquid fuels used for domestic illumination and heating may be divided into three general classes--coal gas, including carburetted water gas and producer gas and their various mixtures; oil gas, acetylene and gasoline gas. Of these the first is the most important as an illuminating gas, while for industrial and domestic purposes producer gas is of no importance as a fuel gas. Gasoline, acetylene and oil gases are generated and used to a remarkable extent in isolated dwellings as fuel and for illumination.

The value of any gas for domestic purposes will depend on the amount of heat that is produced when it is burned. In the earlier days of its use coal gas was employed entirely as an illuminant and its value was expressed in illuminating power; at the present time the standard often prescribed by regulation is that of its illuminating capability and is stated in candlepower. There is, however, a tendency to establish the more consistent standard of expressing the value of gas by its heat value. The reasons for this is the general use of mantle gas burners which depend on the heating value alone for their efficiency and the fact that coal gas is very extensively used for domestic fuel.

=Coal Gas.=--Coal gas is derived from the solid hydrocarbons of coal transformed into the more convenient, gaseous form of fuel by means of distillation. Coal gas was first made by distilling coal from an iron pot over a fire and to some extent this is still the principle of the present practice. The gas as it comes from the retort is subjected to a refining process of washing and scrubbing to remove the undesirable properties when it is stored in a large gasometer for distribution through pipes to its places of use. Coal gas is now used largely for fuel as well as for lighting. Unless the heating value of gas is regulated by law in any community and determinations of its quality are made regularly by some competent official, the amount of heat contained in coal gas is entirely at the option of the manufacturer and manager’s conscience. The value as given in the table on page 252 is the number of B.t.u. coal gas should contain. The heating value of any gas is determined by burning the gas in a calorimeter made expressly for the measurement of the heat of combustion for each foot of the gas consumed.

=All-oil Water Gas.=--In places where an abundant supply of cheap oil is available, all-oil water gas has met with a great deal of favor. It is made by atomizing crude oil by a blast of steam in a heated chamber where a combination of the vaporized oil and steam form a gas. In general the gas resembles coal gas and as given in the table on page 252 is slightly higher in heating value.

=Pintsch Gas.=--One of the commercial adaptations of oil gas is that of the Pintsch process of compressing the gas in tanks for transportation. In the Pintsch process, the gas is subjected to a pressure of 10 atmospheres--about 150 pounds. This condensation permits a sufficiently large volume of gas to be stored in tanks as to make possible the lighting of railroad trains, etc., by gaslight. The pressure of the gas is reduced by an automatic regulating valve to that required by the burner. The flame is very much the same as that produced by coal gas.

=Blau Gas.=--Another commercial adaptation of oil gas is that known as Blau gas. In this process of storage the gas is subjected to 100 atmospheres of pressure--about 1500 pounds. This pressure is sufficient to liquefy the gas and as a result a large amount can be transported in a relatively small space. According to Fulweiler 1 gallon of the liquefied gas will yield about 28 cubic feet of the expanded gas and there will remain a residue that may run up to 9 per cent.

=Water Gas.=--When the vapor of water is brought into contact with incandescent carbon, the water is decomposed and sufficient carbon is absorbed to produce a fuel gas. Its manufacture depends on the decomposition that takes place when steam is blown into a bed of incandescent coal. The gas made by this reaction is a water gas, but due to the fact that when burned it gives a blue flame, it is known as “blue gas.” It has a heating value of about 300 B.t.u. per cubic foot, and as compared with coal gas which gives 622 B.t.u. per cubic foot, would be reckoned at about one-half its value as a heating agent. Blue gas may be rendered luminous by the addition of some hydrocarbon that will liberate free carbon in the flame when burned. This is accomplished in the process of manufacture by the addition of vaporized oil.

The following table as stated by Fulweiler gives the heating values of the gases commonly used for domestic purposes in British thermal units per cubic foot.

Coal gas. 622 B.t.u. Carburetted water gas 643 B.t.u. Pintsch gas. 1,276 B.t.u. Blau gas. 1,704 B.t.u. All-oil water gas 680 B.t.u. Acetylene gas 1,350 B.t.u. Gasoline gas. 514 B.t.u. Oil gas 1,320 B.t.u. Blue water gas 300 B.t.u.

The cost and calorific values as computed by Dr. Willard of the State Agricultural College of Kansas, given below, shows the relative values of various kinds of domestic fuels.

Cost per Cal. per Cal. for pound Gram 1 cent cents

Wood, 20 per cent. H.O. $ 5.00 per cord 0.167 2.3 7,620 Bitu. coal $ 4.25 per ton. 0.213 7.5 16,009 Ant. coal $12.50 per ton 0.625 6.0 4,354 Gasoline, sp. gr. 68 $ 0.14 per gallon, 5⅔ pounds. 2.470 10.0 1,846 Kerosene, sp. gr. 80 $ 0.11 per gallon, 6⅔ pounds. 1.650 10.0 2,753 Coal gas, 1.50 per 1000 cubic feet. 3.100 20.0 2,927 Alcohol, 90 per cent., 50 per gallon, 7.140 6.4 404 7 pounds Electricity, 0.15 per kilowatt-hour 57.4

The relatively high heat value of Blau gas (1704 B.t.u.) and the fact that it may be reduced to a liquid form for transportation has resulted in the manufacture of small lighting plants that may be used in places where other forms of liquid or gaseous fuel are not desirable.

For transportation the gas is compressed in seamless, steel bottles that contain about 20 pounds of liquid. The charged bottles are shipped to the consumer and when empty are returned to the manufacturers to be refilled.

The entire plant--ready to be attached to the distributing pipes in the house--is contained in a steel cabinet. The charged tanks are attached to a larger tank into which the liquid gas is first expanded. This expansion is accomplished by an automatic valve that maintains a constant pressure in the large tank. With this plant the lamps and burners of the stoves are operated as with city gas--no generating or preliminary preparation being necessary. As soon as the bottles are exhausted they are replaced by others and the empty bottles are shipped to the factory to be refilled.

=Measurement of Gas.=--When gas of any kind is purchased from a manufacturing company, the amount used is measured by a gas meter, located at the point where the gas main enters the building. The readings of the meter are taken by the company at stated intervals and the amount registered is charged to the account of the consumer. Gas is sold in cubic feet and is so registered by the meter. The price is quoted by the manufacturers at a definite rate per thousand cubic feet. The difference between the last two readings of the meter furnishes the amount from which the gas bill is reckoned.

The occupants of a building are responsible for all gas registered by the meter and, therefore, should be acquainted with the conditions under which the gas is sold. Gas bills are often the subject of dispute because of failure to understand the period of time covered by the amount claimed; again, the varying length of days due to the season of the year has a pronounced effect on the amount of gas consumed. Lack of care in the economical use of gas is probably the most prolific cause of disputed bills.

The amount due for gas may at any time be checked by the consumer who keeps a record of the meter readings. At any time the correctness of a meter is doubted, arrangement may be made with the gas company to have it tested for accuracy. This is done in the office of the company, by attaching the meter to a measuring device--called a meter prover--in which a definite measured amount of gas is passed through the meter and comparison made with meter registration. If it is found that the meter does not register correctly, the gas company is in duty bound to make good the difference. If, however, the meter is found to be correct, it is customary to charge for the services of proving the meter.

=Gas Meters.=--The gas meter as ordinarily used is shown in Fig. 177. In Fig. 178 the same meter is shown with the top and front exposed.

The meter is operated by the pressure of the gas which enters at the inlet pipe on the left-hand side of the meter as you face the index. The gas from this pipe comes into the valve chamber and passes alternately into the diaphragms and their chambers, as the valve ports _V_ are opened and closed by the action of the meter. The movement of the valve in opening the port which admits gas to the diaphragm closes the port to the chamber which has filled. The gas entering the diaphragm expands it like a bellows and forces the gas out of the chamber, through the middle part of the valve into the outlet pipe _F_. While this action is going on, the gas is entering the case compartment on the opposite side of the meter and also forcing the gas from its diaphragm through the opening _F_.

While the meter is in operation, one of the diaphragms and one of the case compartments are filling while the others are emptying. The movement of the diaphragm discs is transformed to the recording dial by the connecting levers shown at the top of the figure. The movement of these levers is such as to produce a rotary motion to a tangent which is attached to a shaft that operates the recording dial. The tangent is carried around in a circle by the action of the arms and its movement is registered on the index of each cycle of the diaphragms.

The measurement is accomplished by the displacement of a definite amount of gas with each movement of the discs; first, from the chamber and then from the diaphragms.

HOW TO READ THE INDEX

The index of a gas meter looks quite complicated, but it is really a very simple contrivance. The small circle on the top in Fig. 177 is for testing purposes only and need not be considered. The dial of Fig. 177 is shown in Fig. 177_A_. The first circle, marked 1 thousand, registers 100 feet for each figure, 1000 feet for the entire circle. If the pointer stood on 9 it would mean 900 cubic feet. The second circle registers 1000 for each figure, or 10,000 for the entire circle. When the pointer of the first circle has been around once, it reaches 0 on that circle, but the hand on the second has moved to figure 1, showing 1000 feet used. The process goes on until the pointer of the second circle has traveled around and stands at zero. The pointer on the third circle, however, has moved to 1, indicating 10,000. This explanation shows the general plan of the index. A few minutes study of it will render the index as easy to read as the face of a clock. Of course, the pointers do not always stand exactly on the figures as they move from figure to figure as the gas is used.

Suppose your index stood like this:

Take the figure 3 on the 100 thousand circle, the figure 8 on the 10 thousand, and the figure 6 on the 1 thousand, and you have 30,000, 8000, and 600, or 38,600 feet. To ascertain the quantity of gas used in the time elapsing between the readings of the meter, subtract the quantity registered at the previous reading. Thus, if the previous reading was 38,600 feet, and the next reading 40,100 feet, the pointers standing thus:

When 100,000 feet have been passed, the index is at zero; that is, all the pointers stand at 0, and the registration begins all over again.

=Prepayment Meters.=--In many places it is desirable to sell gas in small quantities and to prepay the amount for a given supply of gas. This is accomplished by a meter such as that of Fig. 179. The meter is constructed much the same as the former but provided with a mechanism such that when a coin--usually 25 cents--is deposited, according to the printed directions in the instrument, an amount of gas representing the proportional current rate is allowed to pass the meter. The supply is cut off as soon as the amount paid for is used; when in order to receive more gas, another coin must be deposited as before.

=Gas-service Rules.=--The rules for the regulation of gas service are in many States under the control of a board or commission whose duty it is to form codes prescribing the measurement and sale of all public utilities. The following form, General Order No. 20, State Public Utilities Commission of Illinois, gives an idea of the requirements in that State for the sale of coal gas.

RULE 3. REQUEST TESTS.--Each utility furnishing metered service shall make a test of the accuracy of any meter, upon written request by a consumer: Provided, first, that the meter in question has not been tested by the utility or by the commission within 6 months previous to such request; and second, that the consumer will agree to accept the result of the test made by the utility as determining the basis for settling the difference claimed. No charge shall be made to the consumer for any such test. A report, giving the result of every such test, shall be made to the consumer.

RULE 4. ADJUSTMENT OF BILLS FOR METER ERROR.--If on any test of a service meter, either by the utility or by the commission, such meter shall be found to have a percentage of error greater than that allowed in Rule 11 (see below) for gas meters, the following provisions for the adjustment of bills shall be observed.

(_a_) _Fast Meters._--If the meter is faster than allowable, the utility shall refund to the consumer a percentage of the amount of his bills for the 6 months previous to the test or for the time the meter was installed, not exceeding 6 months, corresponding to the percentage of error of the meter. No part of a minimum, service or demand charge need be refunded.

(_b_) _Slow Meters._--If the meter is found not to register or to run slow, the utility may render a bill to the consumer for the estimated consumption during the preceding 6 months, not covered by bills previously rendered, but such action shall be taken only in cases of substantial importance where the utility is not at fault for allowing the incorrect meter to be in service.

RULE 11. GAS-METER ACCURACY.--(_a_) _Method of Testing._--All tests to determine the accuracy of registration of a gas service meter shall be made with a suitable meter prover. At least two test runs shall be made on each meter, the results of which shall agree with each other within one-half per cent. (1/2%).

(_c_) _Allowable Error._--Whenever a meter is tested to determine the accuracy with which it has been registering in service, it may be considered as correct if found not more than two per cent. (2%) in error, and no adjustment of charges shall be entailed unless the error is greater than this amount.

RULE 15. HEATING VALUE.--Each utility furnishing manufactured gas shall supply gas which at any point at least 1 mile from the plant, and tested in the place where it is consumed, shall have a monthly average total heating value of not less than 565 B.t.u. per cubic foot, and at no time shall the total heating value of the gas at such point be less than 530 B.t.u. per cubic foot.

To arrive at the monthly average total heating value, the results of all tests made on any one day shall be averaged and the average of all such daily averages shall be taken as the monthly average.

RULE 8. RAILROAD COMMISSION OF WISCONSIN.--Each utility furnishing gas service must supply gas giving a monthly average of not less than 600 B.t.u. total heating value per cubic foot, as referred to standard conditions of temperature and pressure. The minimum heating value shall never fall below 550. The tests to determine the heating value of the gas shall be made anywhere within a 1-mile radius of the center of distribution.

=Gas Ranges.=--Gas ranges and all other heaters using gas as a fuel are constructed to utilize the principle of the Bunsen burner. Fig. 180 illustrates the type of burner used in the Jewel gas range. This represents the form adapted to the top burners for all direct-contact cooking or heating. The burners are of different sizes and arranged as they appear in Fig. 181. This picture shows the top of the range as seen from above, looking directly downward. The gas supply pipe and individual valves for each burner are in position as they appear in front of the range.

In operation, the nozzles of the gas valves stand directly in front of the opening _G_, in Fig. 180. The stream of gas in passing into the burner induces a flow of air through the opening _A_. The mixture of gas and air is such as will burn with the characteristic Bunsen flame without smoke.

The oven burners are different in form but the individual flames are the same as those of the top burners. They extend across the oven as shown in Fig. 182. In this the top of the oven is removed and burners as seen are viewed from above.

The top burners are lighted by direct application of a burning match but the oven burners must be lighted by first igniting a special torch or “pilot lighter.” The middle gas valve of Fig. 182 is turned and the torch lighted, then the other valves are opened and the jets are instantly ignited. As soon as they are burning the pilot lighter is extinguished by turning its valve.

The reason for this special lighter is because of the possibility of explosion at the time of lighting. The gas from the jets is mixed with air at the proper proportion to be violently explosive and if by chance the gas should be turned on a sufficient time to fill the oven with this explosive mixture and then lighted, an explosion would be certain, with every possibility of disastrous consequences. All gas ovens should be lighted in a manner similar to that described.

=Lighting and Heating with Gasoline.=--The remarkable growth of modern cities, the building of small towns in the west, and the improvement in suburban and rural homes has created a demand for efficient means of illumination in the form of small household lighting plants. The development and improvement in electric lighting has induced an equal, if not greater, improvement in gas lighting. Up to the year 1875, the open-flame gas jet represented the most improved form of city lighting. Then came electricity, which for a time bade fair to supplant all other forms of illumination; but the relative high cost of electric lighting, even with the advantages it afforded, was a stimulus to improvement in less expensive forms of illuminants.

The invention of the incandescent-mantle gas burner enormously increased the opportunities for gas lighting and opened an inviting field of endeavor. In a relatively short time, three distinct types of gasoline lighting plants for household illumination came into common use, with a great number of different systems in each type. As a means of economical illumination the only rival of any consequence to the small gasoline-gas plant of today is acetylene. The dangers attending the use of these agents of illumination have been rapidly eliminated, until today--when intelligently managed--they are fully as safe as any other means of artificial lighting. Gasoline plants are now in common use in cities where competition with all other forms of illumination require excellence in service to hold an established place.

In order that any mechanical appliance may be used with the best results, its principle of operation and mechanism must be thoroughly understood. In the case of gasoline plants, not only familiarity with the mechanism should be acquired but an intimate knowledge of gasoline and its characteristic properties should be gained, that the peculiarities of the plant may be more fully comprehended.

=Gasoline= is the first distillate of crude petroleum; that is, in the process of separation, the crude petroleum is distilled from a retort and the condensed vapors at different degrees of temperature form the various grades of gasoline, kerosene, lubricating oil, paraffin, etc. The crude oil is placed in the still and heated; the distillate that first comes from the condenser, at the lowest temperature of the still, is gasoline of a light spiritous nature. As the process of distillation continues, this part of the petroleum is entirely driven off and it is necessary to raise the temperature of the still in order to vaporize an additional portion of the oil. There is no distinct line of separation between the gasoline that first comes from the condenser and that which comes over after the temperature is raised, except that it is less of a spiritous nature and contains more oily matter. As the temperature of the retort is gradually raised, the distillate contains less and less of the spiritous and constantly more of the oily matter.

In order to grade gasoline for the market, the standard adopted was that of relative density. The distillations produced at various temperatures are mixed to produce various densities which form definite grades of gasoline. The Beaumé hydrometer is a scale of relative specific gravities in which the different densities are expressed in degrees. The highest grade of gasoline produced by the first distillation is 90°Bé.; that is, the hydrometer will sink in the gasoline to 90° on the scale. As the temperature of the retort is gradually raised, the distillate becomes heavier and the next commercial grade is 86° gasoline. The 86° gasoline contains a greater proportion of oily matter and a less amount of that of a spiritous nature. The next commercial grade that is produced, as the temperature is raised, is 76° gasoline, a still highly volatile spirit but containing more oil than the last. This process is kept up until there is an amount of oil in the distillate that can no longer be termed gasoline, when kerosene is distilled from the retort.

The following descriptions of gasoline and kerosene by B. L. Smith, State Oil Inspection Chemist of North Dakota, gives a definite idea of their properties and the requirements of the law in their regulation and sale.

“Gasoline is formed by the condensation of vapor that passes off at comparatively low temperatures during the distillation of crude petroleum. It has been common practice among refiners to collect as ‘straight’ gasoline all that distillate having a specific gravity above 60°Bé. At present, the name applies broadly to all the lighter products of petroleum above 50°Bé. in gravity, including products obtained from the ‘casing-head’ gases of oil wells, by methods of compression and cooling, and also the ‘cracked’ gasoline formed by the decomposition of heavier oils when subjected to high temperature and pressure.

“It has been the custom to grade and sell gasoline according to ‘high’ or ‘low’ gravity test. Recent study and investigation has shown that specific gravity in itself is of very little value in determining the quality of a gasoline. It may be taken as an index of other properties, particularly its volatility, if information as to its source and method of production are at hand; but under present market conditions a specific-gravity determination is entirely inadequate. The specific-gravity test alone may give a high rating to a poor gasoline and a low rating to a good one. It has been discarded as a standard of comparison by the U. S. Bureau of Mines. It indicates nothing definite about the quality of a gasoline and in many cases it does not even approximate relative values. Volatility, that is, the ease with which it vaporizes, is the fundamental property that determines the grade, quality, and usefulness of gasoline. The Beaumé test, however, must remain the standard for grading gasolene until a more definite measure is adopted.

“The Oil Inspection Law (1917) for the State of North Dakota, states, that: ‘all gasolines, sold or offered for sale in this State for household use, shall, when one hundred cubic centimeters are subjected to a distillation in a flask--as described for distilling of oil--show not less than three (3) per cent. distilling at one hundred and fifty-eight (158) degrees Fahrenheit, and there shall not be more than six (6) per cent. residue at two hundred and eighty-four (284) degrees Fahrenheit, which shall be known as the chemical test for gasoline sold or offered for sale in this State for domestic purposes.’

“Gasoline for household purposes, as for use in cold-process lighting systems should contain not more than a very slight amount of constituents that do not vaporize readily. It is obvious that a gasoline for cleaning or drying purpose should contain no oily or kerosene distillate. On the other hand, the gasoline for use in a gasoline stove or other generator, where heat is employed in its vaporization, may contain a considerable amount of the less volatile oils. The amount of gasoline sold for household use is in very minor proportion to the immense quantity used for motor purposes.

“No hard and fast line differentiates good motor gasoline from bad. In fact standards of quality seem to be varying with advances in engine design, so that what once was poor gasoline can now be successfully used. Improvement in carburetors seem to be keeping pace with the ever increasing amount of kerosene in the ordinary motor gasoline.

“Gravity test cannot be relied upon as indicating the kerosene content. In the laboratories of the Oil Inspection Department for the State of North Dakota, there have been examined two gasolines of the same gravity, 56.2°Bé. at 60°F., but which contains 31 per cent. and 62 per cent. of kerosene respectively, and their distillation range is quite different. On the other hand, there are other gasolines whose boiling range is nearly parallel and similar, yet whose gravities are 50.2°Bé. and 59.2°Bé. respectively. Also a gasoline and a kerosene having a difference in gravity of but 1°Bé. and a difference of nearly 100°F. in the temperature at which they begin to boil and a difference at 200°F. in the temperature at which all had distilled over. The so-called ‘low’-test gasolines average between 35 per cent. and 40 per cent. kerosene. The chief element of advantage in the so-called ‘high’-test gasolines seems to be that they yield a maximum efficiency over a larger range of engine conditions.

“We have a sample of gasoline sold as ‘high’-test gasoline which contains 29 per cent. of kerosene. Indeed it has a high Beaumé gravity (63.70) compared to the average low-gravity gasolines on the market, and it also contains a large amount (14 per cent.) of very easily volatile constituents. Such a product seems to be a blend of very light ‘casing-head’ stock with kerosene of low boiling range to give the ‘high’ gravity.

“It is desirable that a gasoline should contain a certain percentage of very low-boiling constituents, so that engines may start more readily, especially in unfavorable conditions of weather or climate; but a large proportion would be undesirable because of loss through evaporation and the liability of accidental ignition and explosion. A reasonable amount of light volatile material would probably be about 3-1/2 per cent. Again a reasonably low percentage of the very less volatile constituents is desirable to insure complete vaporization at a not too high temperature, say not more than 10 per cent.; but such a gasoline would be expensive. The producers and refiners claim that the present immense demand necessitates the mixture of low-boiling kerosene constituents with the true gasoline fraction.

=“Kerosene.=--The character of this fuel is best understood by comparing it with gasoline, which it in general resembles, except that it is much less volatile. It is obtained from crude petroleum at a temperature just above that (300°F.) at which gasoline passes off. Its chief use is as an illuminant in lamps. It is also increasingly used as a fuel in cooking stoves, small portable heaters, and as a motor fuel for engines and tractors.

“The laws of most States stipulate certain tests which kerosene must meet in order to be approved for general sale. These tests include color, flash point, fire test, sulphur determination, and candlepower tests. The North Dakota Oil Inspection Law (1917) specifies that the color shall be water-white when viewed by transmitted light through a layer of oil 4 inches deep. It shall not give a flash test below 100°F. and shall not have a fire test below 125°F. Such illuminating oils shall not contain water or tar-like matter, nor shall they contain more than a trace of any sulphur compound. The photometric test, when burning under normal conditions, shall not show a fall of more than 25 per cent. in candlepower in a burning test of not less than 6 hours nor more than 8 hours’ duration, consuming 95 per cent. of the oil.

“The flash point of an oil is the lowest temperature at which vapors arising therefrom ignite, without setting fire to the oil itself, when a small test flame is quickly approached near the surface in a test cup and quickly removed.

“The fire test of an oil is the lowest temperature at which the oil itself ignites from its vapors and continues to burn when a test flame is quickly approached near its surface and quickly removed.

“When oils containing sulphur are burned, the sulphur is thrown off in the form of gaseous sulphur compounds. Because of their poisonous nature and their bleaching and disintegrating action on clothing, hangings, wall coverings, etc., it is obvious that to safeguard the health and preserve the furnishings of the home, illuminating oils should contain not more than a trace of sulphur compounds, and that their flash and fire limits should be high enough to insure safety in ordinary use in lamps and stoves.

“The law further specifies as to the boiling limits of kerosene: ‘It shall be the duty of the State Oil Inspector ... to have chemical tests made ... demonstrating whether or no such oils contain more than 4 per cent. residue after being distilled at a temperature of 570°F., and shall not contain more than 6 per cent. of oil distilling at 310°F., when one hundred cubic centimeters of the oil is distilled from a side-neck distilling flask’ of certain specified dimensions.

“This is to insure the kerosene against an excess of easily inflammable material of the gasoline range and thus render it dangerous to the user. In addition it is to insure against an undue proportion of heavy constituent of lubricating oil distillate, which would clog the wick and reduce the efficiency, heating and illuminating value of the oil.”

LIGHTING AND HEATING WITH GASOLINE

The extended use of gasoline as a lighting and heating agent, has brought about the development of a great number of mechanical devices that are intended to furnish the house with an efficient source of illumination and at the same time provide the kitchen with a convenient and relatively inexpensive fuel. These machines are generally simple in mechanical construction and so designed as to eliminate most of the dangers involved in the use of gasoline. In operation, they require a minimum amount of attention when suited to the purpose for which they are intended. That the object of the plants is attained is attested by the great number in use and the degree of satisfaction afforded the users.

The three systems of gasoline lighting referred to above are known commercially by terms which are characteristic of the process involved:

1. The _cold-process_ system, in which the gasoline is vaporized, at the temperature of an underground supply tank, and after being mixed with the required amount of air is sent through the building in ordinary gas pipes exactly as in the case of city gas.

2. The _hollow-wire_ system, in which the gasoline is sent from the supply tank to the burners in a liquid form, where it is vaporized by heat and the vapor mixed with the necessary air to afford complete combustion.

3. The _central-generator_ or _tube_ system, in which the gasoline is sent to a central generator from a supply tank and there vaporized by heat, at the same time being mixed with air in sufficient amounts to render it a completely combustible gas without further dilution.

THE COLD-PROCESS GAS MACHINE

The gas machine of the cold-process type is so constructed that air is forced through a tank or carburetor, containing gasoline and remains in its presence until saturated with gasoline vapor. This saturated air is afterward diluted with additional air, to produce a quality of gas that contains proportions of air and gasoline vapor which will produce complete combustion when burned with an open flame.

Combustion is a rapid chemical change in which heat is evolved due to the union of carbon and oxygen. If the carbon is completely oxidized, the combination produces carbon dioxide (CO₂) and the greatest amount of heat is evolved.

Gasoline being a highly volatile liquid will vaporize at temperatures as low as -10°F., but as the temperature is higher vaporization will be more rapid. In a confined space, at relatively low temperature, such as the carburetor of a gas machine, the vaporization will at first be very rapid; but after the more highly spiritous portion has been evaporated, a considerable part, even of the lighter grades, will be vaporized very slowly. In the cold-process machines, only the lighter grades can be used with success and even then, in inefficient machines, a portion of the lesser volatile gasoline will have to be thrown away. For this reason and for others that will appear later, it is advisable to consider very closely the working properties of the entire plant.

In order to obtain gas that will always be of the same quality and at the same time use gasoline in an efficient manner, the gas machine must be composed of three essential parts: the blower, the carburetor and the mixer.

The blower is that part of the machine which supplies air for absorbing the gasoline vapor and maintaining a constant pressure on the system. It is usually made in the form of a rotary pump, the motive power for which is a heavy weight. The pump may, however, be driven by water pressure furnished by city water pipes or other water supply.

The carburetor is a tank which contains the supply of gasoline and is so constructed as to permit the air from the blower to most readily take up the gasoline vapor. It should be so arranged that when the contained gasoline becomes old and less volatile, the air may remain in its presence a sufficient time to become saturated by slow absorption.

The mixer is that part of the machine which regulates the amount of gasoline vapor contained in the gas entering the distributing pipes. In order to satisfactorily perform its function, it should be so arranged as to permit a constant amount of gasoline vapor to enter the mixture which composes the finished gas. This amount should be such as to produce a bright clear flame in an open gas jet. If the gas contains too great an amount of gasoline vapor, the flame will smoke. If too little gasoline vapor is present, the flames will be pale and lacking in heat.

In Fig. 183, the entire plant is shown in place. It occupies a place inside the building, usually in the basement. In the figure the carburetor is marked 1; the mixer 2 stands at the end of the blower, which is numbered 3. The motive power of the blower is furnished by a heavy weight, which is raised by a block and tackle, the cord of which is attached to the drum and fastened to the shaft of the blower. The force furnished by the weight 4 drives the blower and maintains a constant pressure on the gas in the system. The pipe 8 conducts the air from the blower to the carburetor, which is located underground, below the frost line and 25 or 30 feet away from the building.

The carburetor in this case is also the storage tank, as shown in detail in Fig. 184. The carburetor is divided laterally into two or more compartments, depending on the size of the plant to be accommodated. That shown in Fig. 184 contains four compartments and is intended for a large plant. The construction is such that the compartments are only partly filled with gasoline, and arranged to permit the air from the blower, which enters at the pipe marked air, to pass through each compartment in succession, beginning at the bottom, in order that it may become completely saturated with gasoline vapor. As an additional means of aiding the saturation of the passing air, the compartments in this carburetor are provided with spiral passages through which the air must pass, so that when it reaches the outlet pipe, marked gas, the air is completely filled with gasoline vapor.

The vapor-saturated air now leaves the carburetor by pipe 9, in Fig. 183, and enters the mixing chamber 2, where it is mixed with the required amount of atmospheric air, to make it completely combustible when burned at the burner.

The mixing chamber is shown in detail in Fig. 185. The mixing is done automatically and the quality of the gas is uniform, regardless of the varying conditions of the attending temperature and the quality of the gasoline in the carburetor.

The vitally important feature of any gas machine is, that a constant amount of gasoline vapor be carried to the burners. If the gas contains too great an amount of gasoline vapor, a smoky flame will be the result; if an insufficient amount of gasoline is present, the flame will be pale and give out little light. When freshly charged, the gasoline in the carburetor will vaporize very readily, and a large amount of air must be added to the gas to reduce it to the proper consistency; but from old gasoline, which has lost most of the highly volatile matter, a smaller proportion of atmospheric air will be demanded. For this reason, a mixing regulator that will always deliver gas containing the same amount of gasoline vapor is necessary to give satisfactory service. The mixer shown in Fig. 185 accomplishes this office by reason of the specific gravity of the gas.

As the air in the carburetor takes up gasoline vapor, its specific gravity is increased until the air is saturated; and by adding the amount of atmospheric air necessary for complete combustion the weight is reduced to a definite amount which will be constant. The required mixture will, therefore, always weigh the same amount. The principle on which this mixer works is that described in physics as the principle of Archimedes: “that a body immersed in a fluid will lose in weight an amount equal to the liquid displaced.” In the application of the law, the gas in the mixer is the fluid, and the float--to be described--is the displacing body.

The mixer in Fig. 185, is shown cut across lengthwise. The outside casing is indicated by the heavy black lines. The gas which leaves the opening at the top--marked gas outlet--is a mixture of gasoline and air that may be used for exactly the same purpose and in the same manner as coal gas. It may be used in open-flame gas jets or in the mantle gas lamps for lighting purposes and also as fuel gas for domestic heating. The gas is distributed through the building in ordinary gas pipes which are installed as for any other kind of gas. In Fig. 183 the distributing pipes are indicated by the heavy lines.

The valve in the air inlet, in the bottom of the mixer, controls the amount of air to be admitted. The entering gas from the carburetor being heavier than the desired mixture, will raise the float and in so doing will open the air valve and allow the air from the blower to enter. The float and valve are so adjusted that the desired mixture is attained when the balance beam is level. Any variation in the mixture will change its weight and the valve corrects the change whether it be too much or too little air.

The openings at the bottom, marked _gas inlet_ and _air inlet_, are intended for the admission of the saturated vapor from the carburetor, and the atmospheric air, as required. The float which fills the greater part of the inner space is a light sheet-metal drum, that is tightly sealed and nicely balanced by a counterweight on the opposite end of the suspending bar. The counterweight is made adjustable by the device marked _movable adjusting weight_--in the drawing--which permits the quantity of entering gas to be slightly changed as the gasoline in the carburetor grows old.

The adjustment of the counterweight to suit the gas given off from old gasoline in the carburetor, and the occasional rewinding, to elevate the blower weight, is practically all the attention this plant requires. It is a real gas plant which gives every service that may be obtained from coal gas.

THE HOLLOW-WIRE SYSTEM OF GASOLINE LIGHTING AND HEATING

The hollow-wire system of gasoline lighting possesses the advantage of simplicity in construction and ease of installation that makes it attractive, particularly for use in small dwellings. The ease with which plants of this character are installed in buildings already constructed and its relatively low cost has made it a popular means of lighting. The same principle as that used in the hollow-wire system is applied to portable gasoline lamps in which a remarkably convenient and brilliant lamp is made to take the place of the customary kerosene lamp. Small portable gasoline lamps are now extensively used for the same purpose as ordinary oil lanterns. These lamps are convenient as a source of light, make a handsome appearance and are relatively inexpensive to operate.

The hollow-wire system as commonly employed is illustrated in Figs. 186 and 187. In the gravity type of the system as illustrated in Fig. 186, the supply of gasoline is stored in the upper part of the house in a tank _T_ and conducted to the burners below, through a system of small copper tubes as indicated by the heavy lines in the drawing. The same tank is used to supply the gasoline for the stove _R_ in the kitchen and the lamps _L_ in the different apartments. The gasoline supply in this case, is obtained entirely by gravity. This type of plant is not approved by the National Board of Underwriters but its use is quite generally permitted. The storage of gasoline in this form should be done with caution as carelessness or accident might lead to serious results. With an arrangement of this kind the force of gravity gives the pressure which supplies the burners below but it would not be possible to use the lamps on the same floor with the tank.

Where it is desired to use lamps on both floors, a pressure tank is employed for supplying the gasoline to the lamps, as indicated in Fig. 187. In this plant the pressure tanks _S_, _T_ in the basement, furnish the pressure which forces the supply of gasoline through the small tubes to the lamps _L_ in the different rooms and also to the stove _R_ in the kitchen.

The means of furnishing the pressure for supplying the gasoline to the burners may be a simple tank as that in Fig. 188, or the more elaborate apparatus shown in the double tank of Fig. 189. Either style will give good results but the double tank requires the least attention in operation and is therefore more satisfactory in use.

The tank in Fig. 188 is made of sheet metal of such weight as will safely withstand the pressure necessary in its use. It is arranged with an opening _E_, for filling with gasoline, a pressure gage for indicating the air pressure to which the gasoline is subjected, and two needle valves; _C_, for attaching an air pump and _D_, to which the hollow wire is attached for distributing the gasoline to the places of use. The tank is filled with gasoline to about the line _A_, and then air pressure is applied with an ordinary air pump to say 20 pounds to the square inch. This pressure will be much more than will be necessary to force the gasoline through the tubes but it is intended to last for a considerable length of time.

The principle of operation is that known in physics as Boyle’s law, that “the temperature being constant, the pressure of a confined gas will be inversely as its volume.” That is, if the tank is perfectly tight, the pressure above the line _A_, in the tank, will gradually become less as the gasoline is used and when its level is at the line _B_, where the volume is twice the original amount, the pressure will be one-half what it was originally, and will still be sufficient to force the gasoline through the tubes to the lamps. It is evident that once the tank is charged and the air pressure applied it will require no further attention until a considerable part of the gasoline is consumed. If at any time the pressure in the tank becomes too low to feed the lamps, a few strokes of the pump will raise it to the required amount.

While the single tank does the required work, its use is not perfect because the pressure is constantly varying. If a lamp is set to burn at a definite pressure, any decrease in the gasoline supply due to falling pressure will change the amount of light given by the lamp; while the variation in the pressure of the single supply tank is not great, a more perfect effect is attained in the double type of tank as that of Fig. 189.

The object attained in the use of two tanks differs with different manufacturers. The tank shown in Fig. 183, being intended to maintain a constant pressure on the gasoline, is quite different from those described in Fig. 197 in use with the central-generator system of lighting, to be described later. In Fig. 189 tank No. 1 is for air supply alone and tank No. 2 is the storage tank for gasoline. Between the two tanks is a pressure-regulating valve 6-7, which keeps a constant pressure on tank No. 2 so long as the air pressure of the tank No. 1 is equal or greater than the other. The gasoline in tank No. 2 will therefore be always under the same pressure and when the lamps are once burning the gasoline supply to each lamp will be a constant amount.

Tank No. 2 is separated by the head 13 into two compartments, marked 18 and 19. The connection between the two compartments is made by the valve 15 and the connection 16. The gasoline supply for the lighting system is taken from the lower chamber at the valve marked 17.

It is possible to refill this tank with gasoline while the system is working. To accomplish this, the air supply is cut off from tank No. 1, by closing valve 9 and the valve 15 is closed to retain the pressure on the lower chamber of tank No. 2. The screw-plug is then taken from the tube 12 and the tank refilled. The screw-plug is then returned to its place, the valves 9 and 15 are again opened and the regulating valve immediately restores the desired pressure.

The amount of pressure required on the system will depend on the height to which the gasoline is carried within the building. The pressure is generally 1 pound to each foot in height and to do the best work the pressure must be constant.

These plants may serve as a fuel supply for gasoline stove as indicated at _R_ or any other source of domestic heating. The usual gravity supply tank is replaced by the hollow wire through which is the gasoline from the tank in the basement.

=Mantle Gas Lamps.=--Mantle lamps that are intended for using city gas are much the same in construction as those using the cold-process gasoline gas; the styles of mechanism differ somewhat with manufacturers but all lamps of this kind possess the essential features that are common to all. Either of these gases may be used with open-flame burners, such as Fig. 193, but since the introduction of mantle lamps, the open-flame burners are rarely used for household illumination.

In the incandescent-mantle lamp, the light is produced by heating to incandescence a filmy mantle of highly refractory material. The higher the temperature to which the mantle of a lamp is raised, the greater is the quantity of light produced. The office of the burner is to produce a uniform heat throughout the mantle with the use of the least amount of gas. As ordinarily furnished from the mains, coal gas or gasoline gas is too rich in carbon to be used in mantle lamps without dilution. When gas is burned in a mantle lamp, it must contain sufficient oxygen--which is supplied by the air--to combine completely with the contained carbon and reduce it to carbon dioxide. If insufficient air is supplied, the lamp will smoke and the mantle will soon be filled with soot.

In the use of the various gases--made from coal, gasoline, kerosene, alcohol, etc.--as a fuel for the production of either heat or light, the form of the burner in which the gas is consumed is the most important factor of the system. Without burners in which to generate a satisfactory supply of heat for the desired purposes, mantle gas lamps would never have come into common use. An understanding of the mechanism of the burners of a system is of first importance because of the possibility of the failure of the entire plant through an improper adjustment of the lamps.

If complete combustion of the gas is attained in the burner, the greatest amount of heat will be evolved and the residue will be an odorless gas, carbon dioxide (CO₂). If the gas is not completely burned the odor of the gas is noticeable in the air. Incomplete combustion may be caused by an insufficient air supply, which causes a smoky flame; or if a larger flame is used than the burner is designed to carry, some of the gas will escape unburned. In either case the greatest amount of heat is not developed by the burner.

In most burners, whether for heating or lighting--in which gas, gasoline or alcohol is used as a fuel--the principle of operation is that of the Bunsen tube. One noticeable exception to this rule is the burners used with the central-generating systems where the Bunsen tube is a part of the generator.

The gas generated from any hydrocarbon will burn completely, only after being mixed with air or other incombustible gas, in proportions such as will completely oxidize the carbon contained in the fuel.

In Fig. 190 the familiar laboratory Bunsen burner affords an excellent illustration of the Bunsen principle which forms a part of all burners using gas as a fuel. The gas from the supply pipe issues from a small opening _A_ into a tube _B_ and by the force of its velocity the entering gas carries into the tube above it a quantity of air that may be regulated by the size of the opening. If the gas is burned without being first mixed with air, the flame will be dull and smoky but if air is admitted to mix with the gas, an entirely different flame is produced, the characteristic shape of which is shown in the figure.

The upper part of the flame _C_ is known as the reducing flame; it is blue in color and intensely hot. The portion _D_ is the oxidizing flame; it is pale blue, sometimes light green in color. The lower part _E_ is the gas before it begins to burn. When burning in air, the Bunsen flame gives scarcely any light, all of the energy being expended in heat. In the gas stove where the burners are made up of a great number of small jets, it will be seen that each jet shows the characteristic features of the Bunsen flame.

The incandescent-mantle gaslight takes advantage of the heat generated by the Bunsen flame and produces an incandescent light that has revolutionized gas lighting. The flame of the Bunsen tube is burned inside a mantle which is rendered incandescent by the heat.

The incandescent mantle was invented by Dr. Auer von Welsbach and was known for a long time as the Welsbach light; but improvements in the process of making the mantles, brought other lamps of the same type on the market, when it became known as the mantle lamp. The first serviceable mantles were made in 1891 and from that time there has been a steady development in the gas-lighting industry.

The original mantles were made of knitted cotton yarn, impregnated with rare earths and are still so made; but the most durable mantles are now constructed from ramie or china grass. After being knitted, the mantles are impregnated with thorium nitrate, with the addition of a small quantity of cerium nitrate, and occasionally other nitrates. The mantles are then shaped and mounted; the fiber is burned out and the mantles are dipped in collodion to give them stability for transportation. When placed in the lamp for use, the collodion is first burned off and the remaining oxide of thorium forms the incandescent mantle. One style of mantle is now being made in which the fiber is not burned out until it is placed in the lamp. They are commonly used with gasoline lamps and give very good results.

The first incandescent-mantle gas lamps to be used were of the upright type, such as is shown in Fig. 191, and for a long time they were the only mantle lamps in use. While the upright mantle was a great improvement over the open-flame gas jet, the lamp was not satisfactory because of the shadows cast by the fixture and from the fact that a large amount of the light was lost by being directed upward from the incandescent mantle.

With the development of the inverted type, the mantle lamp was greatly improved. In the use of lamps of any kind, the desired position of the illumination is that in which the light is directed downward. In the inverted type of mantle lamp this feature is accomplished and adds materially to the efficiency of the light, because the rays are sent in the direction of greatest service. The upright mantle lamps are still sold but by far the greater number offered for sale are of the inverted type.

The essential features of all gas lamps used under these conditions are shown in Fig. 192, which represents the common bracket type of lamp. The gas-cock _C_, connects the lamp with the gas supply _G_. The gas escapes into the Bunsen tube, through an opening in the tip _P_, which is so constructed that the amount of gas may be varied to suit the required conditions. The brass screw nut _N_ may be raised or lowered and thus increase or diminish the amount of escaping gas by reason of the position of the pin _P_. If the nut is screwed completely down the pin closes the opening and the gas is entirely shut off. When the lamp is put in place, the burner is adjusted to admit the proper amount of gas and so long as the quality of the gas remains the same, no further adjustment will be necessary. Any change to a richer or poorer gas will, however, require an adjustment of the burner to suit the mantle. The amount of gas admitted is only that which will produce complete combustion in the mantle when combined with the required amount of air. Each burner must, therefore, be designed for the mantle in use.

As the gas leaves the opening above the pin _P_, it enters the mixing chamber of the Bunsen tube and air is drawn at the openings _A_-_A_. The mixture of the gas and air is accomplished in the tube leading to the mantle _M_, where it is burned. In all lamps of this kind, there is a wire screen placed relatively as _S_, the object of which is to prevent the mixture in the tube from exploding--in case of low pressure--and thus cause the gas to ignite and burn at the point of entrance to the tube.

At any time the pressure is insufficient to send a steady flow of gas into the tube, the flame may “flash back” and ignite the gas at the point of entrance where it will continue to burn. If, however, the screen is interposed between the gas supply and the burner, the flame of explosion will not pass the screen.

In lighting the lamp, the gas is turned on and a lighted match is held under the mantle, the explosive mixture of gas and air fills the mantle and escapes into the globe, in which it is usually inclosed. As soon as ignition takes place the gas outside the mantle explodes with the effect that is startling but not necessarily dangerous. The escaping gas continues to burn and heats the mantle to incandescence.

The amount of escaping gas is regulated by turning the gas-cock to produce the greatest brilliance with the least flame outside the mantle. When used for household illumination, the intensity of the light is such as to be objectionable, when used directly; but when surrounded by an opal glass globe to diffuse the light, this is a highly satisfactory and economical means of lighting.

=Open-flame Gas Burners.=--Gas jets of the open-flame type continue to be used to some extent but the more efficient mantle lamp has very largely supplanted lights of this kind. In the past, these gas lights were made in a great many styles and were known under a variety of trade names--the fish-tail burner, the bats-wing burner and the Argand burner--and were at times very generally used for gas lighting.

The common gas jet is illustrated in Fig. 193. The figure shows a bracket fixture which is generally fastened to a pipe in the wall. A swing-joint at _A_ permits the flame _F_ to be moved into different positions. The annular opening _A_ permits the gas to pass to the jet in any position to which the light is moved. The gas-cock _C_ is a cone-shaped plug, which has been ground to perfectly fit its socket. It should move with perfect freedom, and yet prevent the escape of the gas. A slotted screw _N_ permits the joint to be readjusted, should the plug become loose in the socket.

The gas-tips _T_ are made of a number of different kinds of materials and are commonly termed lava-tips but tips for gas and gasoline are frequently made of metal. The bottom of the tip is cone-shaped, which permits it to be forced into place in the end of the tube with a pair of pliers. In size the tips are graded by the amount of gas which they will allow to escape in cubic feet per hour. For example--a 4-foot tip will use approximately 4 cubic feet of gas per hour. They are made in a number of sizes to suit the varying requirements.

=The Inverted-mantle Gasoline Lamp.=--The inverted-mantle gasoline-gas lamp shown in Fig. 194, furnishes a good example of mechanism and principle of operation, when used with the hollow-wire system. This is the bracket style of lamp but the same mechanism is used in other forms of fixtures. Lamps of similar construction are suspended from the ceiling, either singly or in clusters; they are also used in portable form.

In Fig. 194 the lamp consists of a bracket _H_, which is secured to the wall and through the stem of which the gasoline is conducted to the generator by the pipe _W_. The arrows show the course of the gasoline and its vapor as it passes through the lamp. On entering the generator the gasoline first passes, the percolation, through an asbestos wick _B_, the object of which is to prevent the vapor pressure from acting directly on the gasoline in the supply tube. The gasoline passes through the wick _B_, largely by capillary action, as it must enter the generator against a pressure greater than that afforded by the pressure tank. The vaporization of the gasoline takes place in the tube above the mantle _T_, from the flame of which it receives the necessary heat.

In lighting the lamp an asbestos torch saturated with alcohol is ignited and hung on the frame, so that the flame may heat the generating casting _N_. This process usually requires less than a minute, generally about 40 or 50 seconds. The torch supplies heat sufficient to generate the vapor for lighting the lamp, but as soon as lighted the heat from the glowing mantle keeps the generator at the required temperature for continuous supply of vapor.

When the generator is sufficiently heated by the generating torch, the needle valve _N_ is opened by pulling the chain _P_. This allows the gasoline vapor from the generating tube to escape at _G_ into the induction tube _R_. As the vapor enters the induction tube at a high velocity, it carries with it the atmospheric air in quantity sufficient to render it completely combustible. The opening _G_ and the tube together form a Bunsen burner. The lamp is so proportioned as to give a mixture of gasoline vapor and air that will produce complete combustion in the mantle _T_. The portion of the burner _Z_, through which the gas enters the mantle, is a brass tip, filled with a fluted strip of German silver, so arranged that the gas on entering the mantle will be uniformly distributed and that the heat generated will render the entire mantle uniformly brilliant.

One feature of the lamp that requires special attention is the opening _G_, through which the vapor from the generator is discharged into the induction tube. This is a very small opening and occasionally becomes stopped or partly closed. When this occurs the lamp fails to receive the necessary amount of gas, and the light is unsatisfactory. In this lamp, the cleaning needle _Q_ is provided for removing the stoppage. The needle is simply screwed into the opening and forces out the obstruction; when it is withdrawn, the opening is left free. A more convenient device for accomplishing the same purpose is described in the portable lamp, Figs. 195 and 196.

=Portable Gasoline Lamps.=--The portable form of desk and reading lamps for the use of gasoline is made in a great variety of styles. They are sometimes constructed to feed by gravity, but by far the greater number are operated by the pressure method. The portable lamp must be a complete gas plant, with storage tank for the gasoline, pipe system for conducting the gasoline to the lamp, generator and burner. To give satisfactory results, the lamp must be capable of being lighted with the least degree of trouble and operated with the least amount of care. The immense number of lamps of this kind that are sold shows that they meet all of these requirements and have proven satisfactory in operation. Their greatest attractiveness is their capability of giving a very large amount of light at relatively low cost.

Fig. 195 illustrates a portable gasoline lamp in which a convenient and efficient form of generating mechanism is combined with an attractively proportioned exterior. The lamp works on the principle of the hollow-wire system, the base serving as a storage and pressure tank, the frame of the lamp acting as the tube for supplying the lamp with gasoline, and the canopy containing the generating mechanism.

The tank in the base is filled with gasoline at the opening _E_, which is made air-tight by a screw-plug. The plug also contains an attachment piece for the air pump, which furnishes the pressure to the gasoline. The hollow standard reaches to the bottom of the tank and through it the gasoline is forced to the point marked _A_, where the gasoline enters the generating mechanism. This part of the lamp, which is entirely concealed by the lamp canopy, is shown in detail in Fig. 196. The reference letters in Fig. 195 apply to the same parts in the detail drawing.

The gasoline enters an asbestos-packed tube _F_ at the point _A_, and after percolating through the tube, reaches the regulating valve at the point _G_. The hand-wheel _B_ opens and closes the valve, and thus controls the entrance of the gasoline to the generating tube _H_, where it is converted into the vapor. The vapor now needs only the addition of air to make it the desired gas for illuminating the mantle.

The vapor from the generating tube escapes at the small hole _K_, located directly under the mixing chamber _M_. The supply of air is received through the tube _C_, provided with a regulator, which is readily accessible from the outside of the lamp. The mixture of gasoline vapor and air is accomplished as in the other lamps described, through the Bunsen tube _N_. In this case, the Bunsen tube is extended and increased in size to produce a mixing chamber of considerable volume. The mantle is attached to the tip _O_. The tip, like the one already described, is made of German silver and constructed to produce a flame that will entirely fill the mantle.

This lamp is provided with a special means of keeping the opening _K_ free from accumulations. The opening _K_, through which the gasoline vapor escapes from the generator, is very small and a slight stoppage will materially interfere with the flow of the vapor and thus impair the illuminating effect of the light. A lever _D_ operates an eccentric which engages the piece _P_, to which is attached a pin that readily enters an opening _K_, when the lever is turned. Any accumulation which may lodge in the opening is instantly removed and the needle returned to its place by a turn of the lever _D_.

=Central-generator Plants.=--The central-generator or tube system of lighting with gasoline, differs from the other methods described, in the manner of generating and distributing the supply of gas to the lamps. In the hollow-wire system each lamp generates its own gas supply. With the central-generator system the gas for all of the lamps is generated and properly mixed with air in a central generator, and the finished gas distributed through tubes to the different burners and there burned in incandescent mantles. The gas as it leaves the generator requires no further mixing with air and therefore the burners are not of the Bunsen type.

Central-generator gas machines are made in a number of different forms by different manufacturers, all of which are intended to perform the same work but differ in the mechanism employed. The machines are simple in construction and as in the hollow-wire system are capable of using lower grades of gasoline than can be used with the cold-process plants. The gas from a central generator may be used for all purposes for which gasoline gas is employed, either for lighting or heating. One difficulty in the use of the machine is the lack of flexibility when required for only a few lamps or varying number of lights. Although these plants are sometimes used for lighting and heating dwellings, their use is limited, for the reason that variation of the number of lights requires the generator to be regulated to suit the change in the gas supply. The plants cannot be conveniently cut down to one light. Their most general use is that of lighting churches, stores, halls, auditoriums, etc., where a variable amount of light is not demanded. Plants of this character are quite generally used for street lighting and for other outside illumination.

An efficient and simple plant of the central-generator type is shown in Fig. 197. The supply of gasoline is stored in a tank similar to that used with the hollow-wire system and placed in any convenient location. The gasoline is conducted to the generator _G_, through a hollow wire marked _W_. The generator is inclosed in a sheet-iron box, which is located at any convenient place in the building. From the generator the gas is conducted through the tube to the lamps _L_.

In Fig. 198 is shown a diagram of the generator, cut through the middle lengthwise, in which all of the working parts are shown in their relative positions. The reference figures designate the same parts of the generator in Figs. 197 and 198.

In the process of generation the tank is filled with gasoline and pressure applied with the air pump. The tanks described in Fig. 189 might be used to advantage with this plant but the one shown in Fig. 197 is so constructed that the larger tank is used for storage of gasoline. The gasoline is pumped directly into the smaller tank which alone is kept under pressure. The pump _P_ is enclosed in the large tank; at any time it is desired to replenish the supply of gasoline, it is only necessary to open the valve _V_ and pump the necessary supply into the small tank. This transfer may be done at any time without danger from escaping gasoline vapor.

The process of generating the gas is best understood by reference to Fig. 198, which shows the internal construction of the generator. The liquid gasoline is admitted at the bottom through the small pipe _W_, and then enters the space 4, where it is vaporized. The initial flow of gas is generated by heating the generator with an alcohol flame from the iron cup 1, which surrounds the generator. When the generator is heated the gasoline admitted to the generator is immediately vaporized; when, by turning the handle 6, the needle valve 5 opens a small orifice through which the heated gasoline vapor escapes into the tube 7, above.

The blast of vapor issuing from the orifice carries with it air of sufficient volume to render the gasoline vapor an explosive mixture that when burned in the mantle will be reduced to CO₂ gas.

When the initial heating by the alcohol flame is exhausted, sufficient gas has been generated so that part of it may be used as a sub-flame in the gas burner 9, to keep the generator heated. The gas is conducted to the burner from the main tube 11, through the pipe 12-14, as indicated by the arrows. The burner 9 surrounds the generator and the size of the flame is regulated by the valve 15, which is opened an amount sufficient to admit the necessary gas to the burner.

To start the generator, the cup 1 is filled with alcohol and ignited. The needle valve 2 is now opened by turning the hand-wheel 3, admitting gasoline into the generator chamber 4, where the vaporization of the gasoline takes place. The flame from the burning alcohol will heat the generator in about a minute. When the generator is hot, the needle valve 5 is opened slightly, by turning the lever 6, and the gasoline vapor under high pressure blows into the tube 7. As the gasoline vapor is blown into the tube 7, air is drawn in through the opening 8, as indicated by the arrows. The generator is practically a large Bunsen tube from which the mixture of gasoline vapor and air is conducted to the burners by a connecting pipe.

Gas machines operated on this principle are made to accommodate a definite number of lamps. After the lamps are lighted, the amount of gas is regulated to suit the number in use. If at any time it is desired to reduce the number of lamps in operation, the gas supply must be regulated to suit the lights left burning.

As an illustration, suppose that a plant of ten lamps had been burning and that it was desired to reduce the number to six; four of the lamps are extinguished by turning the levers _C_, which control the gas-cocks. The generator which had been supplying sufficient gas for ten lights will continue to produce the same amount until the lever 6 is turned to reduce the supply of gasoline to the required amount for six lamps. This is done by gradually closing the valve 5 until the lamps again burn brightly.

In small plants the least number of lamps that will work satisfactorily at one time is three. Automatic regulators are made for plants of considerable size but do not satisfactorily control the gas when the lamps are reduced below three in number. The gas from these plants may readily be used in kitchen ranges, water heaters and other domestic purposes. Individual plants for operating ranges in restaurants and hotels are in common use. The plants are subject to minor derangements that require correcting as they occur, but as soon as the mechanism and characteristic properties of the plant are known, the correction of any difficulty that may present itself is easily accomplished.

=Central-generator Gas Lamps.=--Fig. 199 shows the general construction and arrangement of the parts of the inverted-mantle lamp used with the central-generator system. In outward appearance the lamp is much like any other inverted-mantle gas lamp, but in arrangement of parts it is markedly different. The gas-cock _C_ is larger than that used with the ordinary fixture, because the opening _O_ must carry a larger volume of gas than that for supplying gas to lamps using the Bunsen tube. In the use of lamps with the Bunsen tube, the gas from the mains is mixed with approximately twenty times its volume of air; with a lamp like that of Fig. 199, where the mixture has already been made in the generator, the conducting tubes and the gas-cock must be relatively very large.

The screen _S_, which corresponds to the screen _S_ in Fig. 192, is quite as necessary as in the other lamp. It not only assures a uniform distribution of the gas in the tube but it prevents the mantle from being broken when the burner is lighted. If this screen is punctured, the explosion which takes place when the burner is lighted will be sufficient to blow out the bottom of the mantle. The burner tip _T_ is practically the same as that used with other mantle lamps.

=Boulevard Lamps.=--Gasoline lamps for outside illumination may be constructed to operate with any of the systems described, but the hollow-wire and the generator systems are most conveniently used, because each post may be arranged as an independent plant. For illuminating private grounds or public thoroughfares, lamps such as are illustrated in Figs. 200 and 201 are very generally used.

The lamp shown in Fig. 200 is of the central generator type in which the storage tank and generator mechanism are located in the base of the post. These lamps are also sometimes constructed with a time attachment in the base of the post, arranged with a clock mechanism so that the light may be automatically extinguished at any desired time.

In Fig. 201 the lamp is of the hollow-wire type and as in the case of the other, the supply tank is in the base of the post. With this system it would be possible to supply several lamps from a common supply tank, provided the hollow wire was protected against damage. The lamps arranged to work on either system, require the same amount of attention and are subject to the same derangements as those for inside service.

=Burners for gasoline stoves= are made in a great variety of forms, each having some special points of excellence that are used to recommend the sale of the stove. The most essential feature of a gasoline stove is the burner, since on its successful performance will depend the satisfaction given by the stove. Many self-generating burners have been devised which have met with a great deal of favor, but the type of burner most widely used and the first to be devised for the purpose is the generating burner similar in principle to the generating gasoline lamp.

The burner is first heated from an outside source, in order to generate sufficient gas to start the flame, after which the heat from the burner will develop the gas supply. With gasoline stoves of this kind, the supply tank is elevated, in order that the force of gravity may give sufficient pressure to send the gasoline into the generator while the flame is burning. In the hollow-wire system the same type of burner is used, but the gasoline is forced into the burner by the pressure in the tank.

In Fig. 202 is shown a sectional view of the burner as it appears in the stove. The supply tank, or hollow wire from the pressure tank, sends the gasoline into the tube _A_ at the bottom of the stove, to which several burners may be attached. The tube _B_, through which the gasoline percolates on its way to the generator, is filled with moderately coarse sand, or other material that is intended to prevent the gasoline from being forced out of the pipe by the pressure that is developed in the generator. The pieces _C-C_ are perforated metal plugs that prevent the escape of the particles of which _B_ is composed.

The generator is a brass casting _D-D_ which is firmly screwed to the top of the tube _B_. A needle-valve _E_ governs the discharge of the gasoline vapor at _G_, where the vapor enters the tube _H_, as indicated at _K-K_. The gasoline vapor enters the open Bunsen tube _H_, and with it is carried the air necessary to produce the required gas for complete combustion. The piece _N_ is the generating cup in which is burned the generating fluid--either gasoline or alcohol. The gasoline from the pipe _A_ percolates through the material in _B_ and flows into the generator. The needle-valve being closed, the space _D-D_ fills with gasoline.

To light the burner, the hand-wheel _J_ is turned, opening the needle-valve a sufficient length of time to allow the gasoline to fill the cup _N_ with fuel for generating the initial volume of vapor. A still better way is to fill the cup with alcohol, because the burning alcohol does not fill the air with smoke and odors, as in the case of gasoline, when used for generating purposes. The generating material having been ignited and burned out, the generator is hot and filled with vapor. The heated generator vaporizes a portion of the contained gasoline and forms sufficient pressure to force the remaining gasoline back through _B_ into the supply tank. The material of the tube _B_ permits only a slow movement of the gasoline and prevents the possibility of surging in the generator.

The initial supply of vapor being generated, the needle-valve may be opened and the gas lighted above the burner _I-I_, where it should burn in little jets at each opening with the characteristic Bunsen flame. It sometimes happens that the generator is not heated sufficiently, by the generating flame, to vaporize the necessary gasoline for starting the burner; in this case liquid gasoline will be forced from the opening _G_, and the burner will flare up intermittently in a red smoky flame. When this occurs the burners must be regenerated.

=Gasoline Sad Irons.=--The use of gaseous or liquid fuel is always attended by an element of danger, because of the possibility of accidental explosion. The use of gasoline, the most highly volatile of all liquid fuels, has, however, come to be very generally used as a source of heat for domestic purposes. The danger of accident in the use of gasoline as a fuel for heating sad irons is largely due to ignorance of the involved mechanism or carelessness in manipulation. A knowledge of the principle included in their operation, together with an observance of the possible cause of accident, will reduce the element of danger to a negligible quantity.

The use of gasoline sad irons has come into favor because of their convenience and economy in operation. These irons, in common with the use of gasoline in its other applications of heating and lighting, are made in a great many forms but the principle of operation is confined to two types.

_First_, those in which the gasoline is forced into the generator by the vapor pressure, from the heated supply tank; and _second_ those in which the pressure is caused by pumping air into the supply tank after the manner of the hollow-wire system of lighting.

The first type of iron is illustrated in Fig. 203. The same iron is shown in Fig. 204, with the top in position for generating vapor pressure necessary to start the burner. The body of the iron A is a hollow casting, designed to receive the generator and burner in such position that the bottom portion of the iron may be uniformly heated. The generator and burner are shown in detail in Fig. 205, in which a sectional view is given of the parts, cut across lengthwise of the iron.

In starting the burner for use, the tank is first filled--not quite full--of strained gasoline. The precaution of straining the gasoline should be taken, to prevent putting into the tank anything that will possibly choke the needle-valve. Alcohol is used for generating the vapor supply, because the flame does not black the iron and fill the room with smoke as in the case when gasoline is used for the purpose. When the alcohol is ignited, the cover is placed in position as shown in Fig. 204, so that the flame may heat not only the generator but also the tank. The object of heating the tank is that the heated gasoline may furnish pressure with which to force the gasoline into the generator. When the alcohol used for generating is almost burned out, the valve _F_ is slightly opened and the burner lighted.

As shown in Fig. 205, the generator _G_ is a brass tube, inclosing the valve-stem _G_, which terminates in the needle-valve _V_. This valve regulates the supply of gas admitted to the burner and is operated by the hand-wheel _F_. When the gasoline in the tank has been heated the necessary amount, the vapor in _G_ is allowed to escape through the valve _V_. The vapor is discharged into the Bunsen tube, and with it the air is carried in through the openings _E_, from both sides of the iron. The burner is a brass tube, slotted as shown at _H_, through which the gas escapes, forming a short flame of large area close to the part of the iron to be heated. The size of the flame is regulated by the hand-wheel _F_.

The tank is entirely closed, the plug _P_ being provided with a lead washer to insure a tight joint. The plug is further provided with a soft metal center which acts as a “safety-plug” in case of overheating. Should the iron at any time become too hot, the soft metal center will melt and the released pressure in the tank will put out the burner flame. The soft metal center may be renewed with a drop of solder. In case the safety-plug at any time is melted, the hot gasoline will spurt from the opening and immediately vaporize. This of course would, in a short time, produce an explosive atmosphere which if ignited would be dangerous. In case of accident the iron should be carried to the open air and the flame smothered with a cloth.

=Alcohol Sad Irons.=--Irons of the same style are also made in which alcohol is used as a fuel. The alcohol irons differ in construction from those using gasoline only in the amount of air that is mixed with the vapor. In general appearance the two styles look very much alike, but in the alcohol iron one of the intakes _E_ is entirely closed and the other opening is partially closed.

The operation of these irons is identical to those using gasoline, but they are preferred by those who fear the use of that fuel. In reality there is little difference in the danger attending the use of the two liquids. It is only fair to say, however, that the use of any highly volatile fuel is attended with some danger when used carelessly, but with a reasonable amount of care and a knowledge of the mechanism of the machine in use the danger is of minor consequence.

In Fig. 206 is illustrated another style of gasoline sad iron, the working principle of which is the same as those already described but the supply tank is not heated to give pressure to the gasoline in the tank. In this iron the tank is located at one side of the iron and pressure is applied with an air pump as in the hollow-wire system of lighting. The burner is generated after the manner of the others and operated in exactly the same manner. The chief difference is that the possibility of excessive pressure through overheating is eliminated.

=Alcohol Table Stoves.=--In the United States the use of alcohol as a fuel has never been extensively employed because of the duty imposed on its manufacture by the Federal Government. In 1896 this duty was removed from denatured alcohol and the cost was sufficiently reduced to permit a great extension in its use as a fuel.

Denatured alcohol is any alcohol to which has been added any of the list of prescribed volatile fluids that will render the alcohol unfit for use in beverages and not materially change its heating value. Denatured alcohol is sold at a price that will permit its use in small flat-irons, table stoves and other forms of burners where small amounts of heat are generated for convenience. At the price of denatured alcohol as generally sold, it cannot compete with gasoline and kerosene as a fuel.

In Fig. 207 is shown a convenient and inexpensive form of table stove, in which the vapor of alcohol is burned in practically the same manner as the vapor of gasoline in the burners already described. The supply of alcohol is stored in a tank _A_, and fed by gravity to the burner _B_, the flame from which resembles that of the ordinary gasoline burner.

The generator _G_ with the other essential parts are shown in detail in Fig. 208. The reference letters indicate the same parts in the detail drawing as in Fig. 207.

The alcohol flows from the supply tank through the pipe _C_ to the generator _G_, which is a brass tube filled with copper wires. The vapor for starting the burner is generated by opening the valve _V_ and allowing a small amount of alcohol to flow through the orifice _C_ into the pan _P_ directly below the generator. The valve is then closed and the alcohol ignited. When the generating flame has burned out, the valve _V_ is again opened and the vapor which has generated in the tube escapes at the orifice _C_ and enters the Bunsen tube _T_, (Fig. 207) carrying with it the proper amount of air to produce the Bunsen flame at each of the holes of the burner.

As in the case of the gasoline burners the orifice _C_ sometimes becomes clogged and it is necessary to insert a small wire to clear the opening. With the stove is provided a tool for this purpose. With stoves of this kind, the supply tank must not be tightly closed, because any pressure in the tank would cause it to become dangerous. The alcohol is fed to the generator entirely by gravity. The stopper of the tank contains a small hole at the top which should be kept open to avoid the generation of pressure should the tank become accidentally heated.

Stoves of this kind may be conveniently used for a great variety of household purposes, and when intelligently handled are relatively free from danger.

=Danger from Gaseous and Liquid Fuels.=--All combustible gases or vapors, when mixed within definite amounts, are explosive. The violence of the explosion will be in proportion to the volumes of the gas and the condition of confinement.

When gasoline or other volatile fuel is vaporized in a closed room, there is danger of an explosion, should the mixture of the vapor and air reach explosive proportions. It is dangerous to enter a room with a lighted match or open-flame lamp, where gaseous odor is markedly noticeable. In case of danger of this kind the windows and doors should be immediately opened to produce the most rapid ventilation.

In the act of igniting the flame in a gas or vapor stove, the lighter should be made ready before the gas is turned on. Explosions in gas and vapor stoves are usually due to carelessness in igniting the fuel. It should be kept constantly in mind that, if a combustible gas is allowed to escape and mix with air in any space and then ignited, an explosion of more or less violence is sure to occur.

Gasoline and kerosene are lighter than water and will float on its surface. The flames from these oils are aggravated when water is used in attempting to extinguish them. The burning oil floating on the surface of the water increases the burning surface.

Burning oil must be either removed to a place where danger will not result or the flames must be smothered. In case of a small blaze, the fire may be extinguished with a cloth, preferably of wool, or if circumstances will permit, with ashes sand or earth.

Alcohol dissolves in water and may, therefore, be diluted to a point where it will no longer burn.

ACETYLENE-GAS MACHINES

Acetylene is a gas that is generated when water is absorbed by calcium carbide, after the manner in which carbonic acid gas is evolved when lime slakes with water, but with the liberation of a larger amount of the combustible gas.

Calcium carbide is a product resulting from the union of lime and coke, fused in an electric furnace to form a grayish-brown mass. It is brittle and more or less crystalline in structure and looks much like stone. It will not burn except when heated with oxygen. A cubic foot of the crushed calcium carbide weighs 160 pounds.

Calcium carbide--or carbide as it is ordinarily termed--may be preserved for any length of time if kept sealed from the air, but the ordinary moisture of the atmosphere gradually slakes it and after exposure for a considerable time it changes into slaked lime. The carbide itself has no odor, but in the air it is always attended by the penetrating odor of acetylene, because of the gas liberated by the moisture absorbed from the air.

If protected from moisture, calcium carbide cannot take fire, being like lime in this respect; it is therefore a safe substance to store. It is transported under the same classification as hardware, and will keep indefinitely if properly sealed.

A pound of pure carbide yields 5-1/2 cubic feet of acetylene, but in commercial form, as rated by the National Board of Fire Underwriters, lump carbide is estimated at 4-1/2 cubic feet per pound. In the generation of acetylene, exact weights of carbide and water always enter into combination, _i.e._, 64 parts of carbide to 34 parts of water, and a definite amount of heat is evolved for each part of carbide consumed.

Uncontrolled, the gas burns with a bright but not brilliant flame and with a great deal of smoke, but when used in a burner suited for its combustion it burns with a clear brilliant flame of a quality approaching sunlight. While carbide is not explosive nor inflammable, it may, if it finds access to water, create a pressure such as to burst its container, and it is not impossible that heat might be generated sufficient to ignite the gas under such conditions. That such condition would often occur is not at all probable. When water is sprinkled upon carbide, in quantity such that it will all be taken up, the resultant slaked lime is left dry and dusty, and occupies more space than the original carbide. When more than enough water is employed, the remaining mixture of lime and water is whitewash.

Chemically considered, acetylene is C₂H₂; it is composed of carbon and hydrogen and belongs to a class of compounds known as hydrocarbons, represented in nature by petroleum, natural gas, etc. It is composed of 92.3 per cent. carbon and 7.7 per cent. of hydrogen, both combustible gases. It is a non-poisonous, colorless gas, with a persistent and penetrating odor. Its presence in the air, to the extent of 1 part in 1000 is distinctly perceptible. When burning brightly in a jet, there is no perceptible odor. When completely burned it requires for its combustion 2-1/2 times its volume of oxygen.

All combustible gases, when mixed with air and ignited, produce more or less violent explosions. Acetylene is no exception to the rule, and when allowed to escape into any enclosed space it will quickly produce a violently explosive mixture, so that it is always dangerous to enter a room or basement with a lamp or flame of any kind where the odor of gas is perceptible. This is quite true with a combustible gas of any kind, but with acetylene all mixtures from 3 to 30 per cent. are capable of being exploded with greater or less violence.

The kindling point of acetylene is lower than coal gas or gasoline gas. To ignite either of the latter gases, a flame is necessary to start the combustion, but a spark or a glowing cigar is sufficient to ignite acetylene. It should therefore be borne in mind that acetylene is not only explosive when mixed with air but that it is very easy to ignite. Under ordinary pressures pure acetylene is not explosive, but at pressure above 15 pounds to the square inch explosions sometimes occur where proper precautions are not observed. At all pressures such as are required for household purposes acetylene is as safe for use as any other gas.

Although acetylene is in danger of exploding when under pressure, it is perfectly safe, when the proper conditions are observed, in tanks for a great many kinds of portable lights.

Where acetylene is used in portable tanks under pressure, advantage is taken of its solubility in acetone. This is a product of the distillation of wood which possesses the property of absorbing acetylene to a remarkable degree. In addition to this property is the more important one of rendering the acetylene non-explosive when under pressure. The tanks for its storage are filled with asbestos or other absorbent material that is saturated with acetone. The acetylene is then forced into the tanks under pressure and is absorbed by the acetone. The safety of this means of storage lies in the degree of perfection to which the tanks are filled with the absorbent material. There must be no space anywhere in the tank where undissolved acetylene can exist. Its freedom from danger under such conditions has been thoroughly demonstrated in its use for railroad and automobile lamps.

The use of acetylene as a fuel for cooking and for the various other purposes of domestic use is successfully accomplished in burners that give the blue flame desired for such purposes. Complete cooking ranges and various other heating and cooking devices are regularly sold by dealers in heating appliances, while water-heaters, hot-plates, chafing-dish heaters, etc., are as much a possibility as with any other of gaseous fuel and in as reasonably an inexpensive way.

Coal gas, containing as it does sufficient carbon monoxide to render it poisonous, will cause death when inhaled for any length of time, but acetylene under the same conditions will have no deleterious effect.

=Types of Acetylene Generators.=--There are two general methods of generating acetylene for domestic illuminating and heating purposes: that of adding carbide to water, and that in which the water is mixed with carbide. The two types are illustrated in the diagrams shown in Figs. 209 and 210. The first method, that in which the carbide is dropped into water, is shown in Fig. 209. The tank _A_ is the generator and _B_ is the receiver or gas-holder. The tank _A_ holds a considerable quantity of water and is provided with a container _C_ for holding the supply of carbide. The tank _A_ is connected with the gas-holders by a pipe which extends above the water line in the tank _B_, where the gas is allowed to collect in the gas-holder _G_. A charge of carbide, sufficient to fill the holder with gas, is pushed into the tank _A_ by raising the lever _H_. Immediately the water begins to combine with the carbide and the bubbles of gas pass up through the water and are conducted into the tank _B_. The holder _G_ is lifted by the gas and its weight furnishes the pressure necessary to force the gas into the pipes, which conduct it to the burners. If this machine were provided with the proper mechanism to feed into the generator a supply of carbide whenever the gas in the holder is exhausted, the machine would represent the modern “carbide to water” generator.

The “water to carbide” generator is shown diagrammatically in Fig. 210. As in the other figure, _A_ is the generator and _B_ is the gas-holder. A supply of carbide _S_ is placed in the generator and water from a tank _C_ is allowed to drip or spray onto the carbide. The gas collects in the gas-holder as before. This apparatus represents in principle the parts of a machine for generating acetylene by this process. The actual machines are arranged to perform the functions necessary to make the machines automatic in their action.

Whatever the type of the machine, the object is to keep in the holders a sufficient amount of gas with which to supply the demand made on the plant. Machines representing each of the types described are to be obtained, but the greater number of those manufactured are of the “carbide to water” form.

In the formative period of acetylene generators many accidents of serious consequence resulted from imperfect mechanism. Imperfections have been gradually eliminated until the machines which have survived are efficient in action and mechanically free from dangerous eccentricities.

The qualities demanded of a good generator are: There must be no possibility of an explosive mixture in any of the parts; it must insure a cool generation of gas; it must be well-constructed and simple to operate; it should create no pressure above a few ounces; it should be provided with an indicator to show how low the charge of carbide has become in order that it may be recharged in due season, and it must use up the carbide completely.

Because of the fact that the greater number of acetylene-gas machines of today are of the “carbide to water” type, in the description to follow that type of machine is used. They are generally made in two parts, one part containing the generating apparatus and the other acting as gasometer (gas-holder), but some machines are made in which one cell contains both the generator and gasometer.

In Fig. 211 is shown a two-part, gravity-fed machine, in which all of the internal working parts are exposed to view. The tank (_a_), as in the diagram, is the generator and the tank (_b_) contains the gasometer marked _G_. Each tank possesses a number of appliances which are necessary to make the machine automatic in its action. The part _C_ of the generator contains the supply of carbide, broken into small pieces, a portion of which is dropped into the water whenever additional gas is required. The feed mechanism _F_ is controlled by the gasometer bell _G_, which is buoyed up by the gas it contains. When the supply of gas becomes low, the descending bell carries with it the end of the lever _F_, which is attached to the feed valve; this motion raises the feed valve and allows some of the carbide to fall into the water. The gas that is immediately generated passes into the gasometer through the pipe _P_, and as the bell is raised by the accumulating gas the valve _V_ is closed.

The gas as it enters the gasometer passes through a hollow device _W_, that looks like an inverted T, the lower edge of which is tooth-shaped and extends below the surface of the water. The gas, in passing this irregular surface, is broken up and comes through the water in little bubbles, in order that it may be washed clean of dust. This device also prevents the return of the gas to the generator tank during the process of charging.

The gas escapes from the bell through the pipe _S_ to the filter _D_, where any dust that may have escaped the washing process is removed by a felt filter. It finally leaves the machine by the pipe _L_, at which point it enters the system through which it is conveyed to the different lighting fixtures.

It will be noticed that the tank (_b_) is divided into two compartments, the upper portion containing the water in which the gasometer floats. The lower compartment is also partly filled with water which acts as a safety valve to prevent any escape of gas into the room in which the generator is located. The lower end of the pipes _P_ and _S_ are immersed in the water at the bottom chamber of the tank, from which the gas could escape in case too much is generated and finally exit through the vent pipe _U_ to the outside air.

The float _A_ in the tank (_a_) is a safety device that prevents the introduction of carbide unless the tank contains a full supply of water. The float is a hollow metal cylinder connected by a rod to a hinged cup under the bottom opening of the carbide holder. When the water is withdrawn from the generator, the float falls and the cup shuts off the carbide outlet.

The accumulation of lime, from the disintegrated carbide, requires occasional removal from the tank (_a_); the valve _K_ is provided for this purpose. The lever _S_ is used to stir up the lime which is deposited on the bottom of the tank, that it may be carried out with the discharged water.

Machines of this kind that are safeguarded against leakage of gas or the possibility of accumulated pressure are practically free from danger in the use of acetylene. The accidental leakage of gas from defective pipes and fixtures produce only the element of risk that is assumed with the use of any other form of gas for illuminating purposes.

Acetylene is distributed through the house in pipes in the same manner as for ordinary illuminating gas. The sizes of the pipes to suit the varying conditions of use are regulated by rules provided by the National Board of Fire Underwriters. These rules state definitely the sizes of pipes required for machines of different capacities. Rules of this kind and others that specify all matters relating to the use of acetylene may be obtained from any fire insurance agent.

The general plan of piping is shown in Fig. 212. The generator _G_ is in this case a “water to carbide” machine and is shown connected to the kitchen range, as well as the pipe system which may be traced to the lamps in the different rooms, to the porch lights and to the boulevard lamp in front of the building.

The type of burner used in acetylene lamps is shown in Fig. 213. The gas issues from two openings to form the jet as it appears in the engraving. These burners are made in sizes to consume 1/4, 1/2, 3/4, and 1 foot per hour depending on the amount of light demanded.

=Gas Lighters.=--The acetylene gas jets are lighted ordinarily with a match or taper but electric igniters are often used for that purpose. Electric lighters for acetylene lamps are practically the same as those used with ordinary gas lamps but they must be adapted to the type of burner on which they are used. Electric igniters that are intended to be used with lamps placed in inaccessible places are different in construction from those within reach. In Figs. 214 and 215 are illustrated two forms of igniters that are intended to be used on bracket or pendent lamps. They differ in mechanical construction to suit two different conditions. Fig. 214 is an igniter in which is also included the gas-cock. The gas is lighted by pulling a cord or chain attached to the lever _L_. The movement of this lever turns on the gas and at the same time brings the piece _C_ in contact with the wire _A_ to complete an electric circuit. As the contact between these two pieces is broken, a spark is formed that ignites the gas escaping from the burner at _B_. On releasing the lever a spring returns the piece _C_ to its original position. The light is extinguished by a second pull of the lever.

Fig. 215 illustrates a style of igniter which may be attached to an ordinary gas-cock. It is attached to the stem of the burner by a clamp _D_. The gas is turned on by the usual gas-cock and by pulling the chain at the left the jet is lighted. In pulling the chain the arm _A_ is raised and carries with it the arm _B_. When the arms _A_ and _B_ touch, an electric circuit is formed with a battery and spark coil. When the desired position of the arms is reached, the points separate to form an electric flash which lights the gas.

Fig. 216 illustrates in _A_ the method of installing electric igniters like those described. A battery _B_ and a spark coil _S_ are joined in circuit as shown. The gas pipe acts as one of the wires of the circuit. A battery of four dry cells is commonly used for the purpose. The spark coil is a simple coil of wire wound on a heavy iron core, which serves to intensify the spark when the circuit is broken. In using the igniter, it is only necessary to see that the cells are joined in series with the coil and attached to the insulated part of the igniter. As already explained the action of the igniter is to close the circuit and immediately break the contact at a point where the spark will ignite the gas. On being released the igniter returns to its original position.

In the fixture shown at _C_ is an igniter such as is used in places that cannot be conveniently reached. To light the jet, the circuit is completed by turning the switch at _W_. As soon as the gas is lighted the switch is again turned to break the igniter-circuit. In this device the current passes through a magnet coil in the igniter which acts to open and close the circuit with the same effect as in the others.

=Acetylene Stoves.=--Stoves in which acetylene is used as a fuel are quite similar in construction to those which burn coal gas. The principle of operation is that of mixing the acetylene with air in proper proportion so as to produce complete combustion when burned.