Part 13

The cleanliness of gas, as compared with candles or oil, is a further recommendation; and for the purpose of lighting streets, shops, factories, public buildings, and halls, it presents important advantages; but it is not well adapted for small sitting rooms, because the heat of the flame makes it unpleasant and injurious to the eyes when near, and, unless very pure, it deteriorates the air of closed apartments. In many parts of the country, however, where coals are cheap, and the price of gas is consequently less than in London, it is introduced into every room of nearly all private houses.

The best kind of gas made from mineral substances is produced by the distillation of a bituminous shale, called Boghead coal, which was discovered a few years since in Scotland. One ton of this material yields 15,000 cubic feet of gas, which is equal in illuminating power to 1,930 lbs. of sperm candles. Boghead coal is now commonly used for mixing its gas with that of inferior quality, to bring up the illuminating power to the required standard.

Olefiant gas, made from oil, burns with a brighter and purer light than common coal gas, but it is more costly. It is made nearly in the same manner, by distillation in retorts; the principal difference consisting in the degree and regulation of the temperature. A dull red heat is the best, and in order to keep the oil exposed to the action of an invariable heat, it is admitted gradually into the retorts, into which pieces of brick or coke are inserted to increase the heating surface. One pound of common oil yields about 15 feet of olefiant gas. The same kind of gas may also be obtained in smaller quantities by the distillation of tar, rosin, or pitch. Twelve cubic feet of gas may be obtained from one pound of tar, and ten from the same weight of rosin.

The brilliancy of gas-light depends, in some measure, on the kind of burner employed. To obtain a steady light, an argand burner is usually adopted; the gas being allowed to escape through a number of minute holes pierced in a hollow ring of metal, which admits a current of air through the middle. To increase the supply of air, the burner is covered with a glass chimney, which, if not too long, adds to the brilliancy of the flame; but a very long chimney produces so strong a current of air, as to cool the flame, and diminish the light. A plan is sometimes adopted of placing a small metal disc a short distance above the jets, so as to spread the flame. By this means the brightness is increased, by exposing the flame more directly to the current of air; and the metal disc, by becoming heated, also tends to aid the combustion of the carbon.

One of the problems to be solved on the original formation of gas works was the size of pipes, and the amount of pressure required to force the gas to the various burners. It was at first supposed that the friction against the pipes would oppose so much resistance to the passage of the gas, that it could not be transmitted to great distances. It was found, however, that the perpendicular pressure of a few inches of water was quite sufficient to force the gas through the mains and small pipes of an extensive range of streets. A bold attempt was made at Birmingham, in 1826, to bring gas from the collieries, at a distance of ten miles from the town. The plan was laughed at by many as impracticable, but it was attended with complete success. The gas being made near the mouth of the coal-pit, the cost of conveyance was saved by the additional outlay in the first instance. It must be observed, however, that it is extremely difficult in practice to avoid the escape of gas at the junctions of the pipes; and by increasing the length of the gas mains, the greater will be the leakage. The loss from this cause, in some gas works, exceeds 20 per cent. of the gas manufactured.

The volume of gas discharged from a pipe is directly proportional to the square of its diameter, and inversely as the square of its length. Thus, if a pipe required to discharge 250 cubic feet of gas in an hour, at a distance of 200 feet, must have an internal diameter of 1 inch; to discharge 2,000 feet in an hour, at a distance of 1,000 feet, would require a diameter of 4·47 inches. The same quantity discharged at double the distance would require a pipe 5·32 inches in diameter; at a distance of 4,000 feet the diameter must be increased to 6·13 inches; and at a distance of 6,000 feet the diameter should be 7 inches.

On the first introduction of gas-light, the companies who supplied it charged a fixed sum for each burner of a given size. This mode of charging was, however, very unsatisfactory, for the size of the burner is a very uncertain indication of the quantity of gas consumed. Persons using gas desired to pay for the quantity they actually burned; and to enable them to do this, a special contrivance was invented by Mr. Clegg, the engineer of the Chartered Gas Company, called a gas-meter. That instrument measures, with sufficient accuracy for practical purposes, the volume of gas that passes through it to the burners, and thus each consumer of gas now pays only for the number of cubic feet consumed.

The accompanying diagrams represent sections of a gas meter, as seen in front and edgewise. The outer case of the instrument, which is a flat cylinder made of sheet iron, is indicated by the letters _c_, _c_. Inside it there revolves another cylinder, made also of thin sheet iron, and divided into four compartments, marked _d_, _d_, _d_, _d_. This interior cylinder readily revolves on an axis, _g_, _g_, shown in the section of the instrument as seen edgewise. The gas enters from the street pipe through the opening, _a_, and it is forced out to the burners through the pipe, _b_, the latter being seen in the narrow section only. In that diagram, also, there is shown a cog-wheel, _h_, fixed on to the axis, and a small outer case, in which that wheel rotates. Water is poured into that external case until the gas-meter is rather more than half filled, the level of the water being shown at _i_.

The action of the instrument will be readily understood by examining the two sections. The gas, on entering the tube, _a_, presses against the upper surface of the compartment that happens to be then above it, and tends to turn the inner cylinder round. This pressure forces the gas through the opening, _b_, to the burner; and as the compartment then in communication with that opening is emptied of the gas it contains, in the direction of the arrow, it is gradually forced under the level of the water, and the other compartment, which has in the meantime been filling with gas, continues the supply. Thus, supposing each division of the inner revolving cylinder to hold 108 cubic inches, a complete revolution would indicate that the fourth part of a cubic foot had passed through the pipe, _b_, to the burners. Several cog-wheels, arranged like clock-work mechanism, are connected with the wheel, _g_, and by this means the number of cubic feet of gas consumed is indicated by hands fixed to the wheels, and pointing to the corresponding figures on a series of dials.

Some inconvenience and irregularity having been experienced in the use of the wet meter, the correctness of which, it is evident, may be affected by variations in the height of the water level, dry meters have been constructed for measuring gas, by causing it to pass through a small expanding chamber, similar in principle to a pair of bellows. The objection to these instruments is that the leather, or other flexible substance that forms the sides of the expanding chambers, becomes rigid by use, and the valves are liable to get out of order; but in the last improvement of the instrument, by Mr. Croll, these objections are stated to be effectually removed.

Numerous attempts have been made to produce illuminating gas from other substances than coal, but without advantage. The plan that promised the most success was the production of hydrogen gas by the decomposition of water, which was passed over heated coke in retorts, and by that means the oxygen of the water, combined with the incandescent coke and the hydrogen, was set free. The gas thus collected possessed little illuminating power, but it was afterwards mixed with the rich gas from cannel coal, and raised to the requisite illuminating standard. It was found, however, in practice, that the compound gas thus formed was more costly than ordinary coal gas, and the plan has been discontinued. Another method of giving illuminating power to water gas was to surround the flame with platinum gauze, which was rendered incandescent by the heat, and became highly luminous. But it required twice the quantity of gas burned in this manner to produce a light equal to that of carburretted hydrogen, and the combustion of so much hydrogen gas produced an amount of vapour and heat that were very unpleasant. That mode of gas illumination, called the "Gillard light," from the name of the inventor, was also found more costly than the ordinary mode of lighting with coal gas, which has now no rival to compete with it in economical illumination.

No Act of Parliament is now required, as originally proposed by Mr. Winsor, to enforce the burning of coal gas. Its advantages, in point of economy, cleanliness, and even of safety, are sufficiently understood to spread the use of coal gas to every part of the kingdom. In the metropolis alone there are twelve gas companies, who receive for the sale of gas an average of £100,000 per annum each, thus making the sum paid for gas lighting in London £1,200,000, and it has been estimated as high as £2,000,000. Taking the average price to be 4s. 6d. per thousand cubic feet, the quantity of gas consumed amounts to 5,300,000,000 cubic feet; and if we add to that quantity 20 per cent. for leakage through the mains and pipes, the quantity of gas manufactured in the metropolitian gas works is upwards of 6,000,000,000 cubic feet in a year. It may, perhaps, give a clearer notion of this immense quantity to say, that a gas-holder, capable of containing it, would require to be one mile in diameter, and the height of St. Paul's Cathedral. The light produced by burning such a volume of gas would be equal to that of 150,000 tons of mould candles, which would cost £13,000,000. The quantity of coals requisite for the production of the gas manufactured annually in London is upwards of 600,000 tons.

THE ELECTRIC LIGHT.

The Electric Light is the brightest meteor that has flashed across the horizon of promise during the present century. When first exhibited as a means of illumination, about twelve years ago, the splendour of the rays emitted, and the delusive representations of the small cost required to produce such a brilliant light, led the public to believe that the career of gas-lighting was drawing to a close, and that night would be turned into day by this wonderful demonstration of electrical power. The light produced by charcoal points, subjected to the action of a powerful voltaic battery, was, however, no novelty at that time; for as far back as 1810, Sir Humphry Davy was accustomed to exhibit that development of electrical force at the Royal Institution, and it formed a standard experiment in most chemical lectures. But it seems not to have been thought applicable in those days to the purposes of illumination; and when Mr. Staite brought it into notice, and exhibited its effects on the tops of some public buildings, it was considered one of the most wonderful inventions of the age.

Mr. Staite's patent, taken out in 1847, though commonly supposed to be for the Electric Light generally, was limited in its clauses to the construction of a voltaic battery and apparatus, adapted for maintaining constancy, and for giving steadiness to the light. The merely temporary continuance of the _voltaic arc_, as it was formerly called, seemed indeed to preclude the possibility of its adoption as a means of illumination; it was therefore a great point gained to give stability and constancy to the light. The difficulty of accomplishing this will be perceived when it is known that the charcoal points, between which the action takes place, are constantly undergoing change, the particles of carbon being transferred from one to the other. There is no actual combustion of the charcoal, in the ordinary meaning of the term; the action is principally confined to the transfer of the charcoal connected with the positive pole, to that connected with the negative pole of the voltaic battery, a hollow being formed in one, and a pyramidical accumulation of particles in the other. This action was beautifully shown by Professor Faraday at the Royal Institution last year, by projecting the image of the charcoal points on to a screen, by means of the Electric Light itself. The image, magnified by the lenses of the electric lamp, could thus be distinctly seen without being too brilliant to dazzle the eyes. The particles of carbon, heated to whiteness, were perceived to be in active motion, and the piling up of the pyramid in one, and the hollow produced in the other, were continually varying the distances between them, and thus tending to cause unsteadiness in the light.

Numerous contrivances have been adopted for the purpose of keeping the points at exactly the same distance, as the want of stability was supposed to be the only obstacle to the adoption of the Electric Light. These contrivances have so far succeeded, that a tolerably steady light can be maintained for some time, but under the most careful management the points occasionally approach too near or are too far apart to maintain an equable light.

Among other inventions to increase the steadiness of the light is one that was patented in 1856, by Mr. Way, in which mercury is substituted for charcoal, but the steadiness of light to be thus acquired must be attained with a great loss of illuminating power, and the vapour arising from the combustion of the mercury would be extremely injurious to health.

Mr. Hearder, of Plymouth, has produced more brilliant effects with the Electric Light than any other person. Some remarkable exhibitions of the power of the light were made by him, in April, 1849, from the top of the Devonport Column, and several scientific gentlemen undertook to make observations at different localities to a distance of five miles. At Tremeton Castle, on the banks of the Tamar, a distance of nearly 3½ miles; the light cast a strong shadow, and writing could be distinctly read by it. The space illuminated was at least three quarters of a mile broad. To aid the effect, a reflector was employed, and when the rays were directed to the clouds, they had the appearance of a huge comet, the reflector being the nucleus. The intensity of the light was ascertained to be equal to that of 301,400 mould candles of six to the pound, whilst the light of the Breakwater Lighthouse was equal to only 150 candles. At a distance of five miles the light was sufficiently powerful to enable persons to read a book.

The battery employed by Mr. Hearder in these brilliant experiments consisted of 80 cells of a Maynooth battery, 4 inches square, and the carbon cylinders between which the light appeared were formed of powdered coke, mixed with tar, and rammed into a tube three quarters of an inch in diameter. When these cylinders are about a quarter of an inch apart, the Electric Light appears at the end of each for the space of more than half an inch. The light, during the experiments at Plymouth, was maintained for three hours, and the materials employed amounted to one pound and a-half of zinc, 114 fluid ounces of sulphuric acid, the same quantity of nitric acid, and six pounds of muriate of ammonia.[14]

The most serious practical objection to the introduction of the Electric Light, as a means of general illumination, is its expense. When the project was first brought into notice, attempts were made to show that the battery power required might be obtained at little cost, and in this respect some deceptions were practised not creditable to the parties engaged in promoting the scheme. It has been proved by Mr. Grove that the cost of ordinary batteries necessary to maintain the light in full brilliancy would greatly exceed the price of an equal light from gas.

A plan was patented for generating the required voltaic power, free from cost, by applying the residual sulphate of zinc as paint, and an Electric Power and Light Company was formed to carry out the project. But the plan failed, and the affairs of the company have recently been "wound up."

Until some cheaper mode of generating electricity than is at present known be invented, there is no hope of the Electric Light becoming generally available, but there are special circumstances in which it may be applied with advantage. It is peculiarly applicable for lighthouses, as its rays would penetrate through a foggy atmosphere that would obscure the light of ordinary flames, and in such cases the extra cost should not operate as an obstacle to its use.

INSTANTANEOUS LIGHTS.

Those who are not old enough to remember the time when flint-and-steel were the implements employed to obtain a light, can have no sufficient appreciation of the great convenience of "Lucifer" matches. In those "good old times," it was a regular household care to provide a sufficiency of tinder, to see that it was kept dry, and that there was a proper flint "with fire in it." The striking of a light, when the tinder-box was adequately supplied, was no mean accomplishment; and the unskilful hand, operating in the dark, would either get no sparks at all, or send them in a wrong direction, and not unfrequently strike the skin off the knuckles, in the vain endeavour to set light to the tinder. Or if the tinder were damp, the sparks would fall upon it without igniting, and minutes would be spent in holding a pointed brimstone match to the delusive spark, and blowing at it without effect. Sometimes the incautious operator, tired with his fruitless efforts, would sprinkle gunpowder over the tinder, to make it take fire more readily, and whilst puffing at a long-desired spark, the gunpowder would explode in his face and nearly blind him. Such were some of the annoyances, attended by loss of time, that were experienced in obtaining the same result that is now produced instantaneously, and much more effectively, by merely rubbing the match against any rough surface.

Several attempts had, indeed, been made many years ago to supplant the flint-and-steel and tinder-box, and some of the plans adopted so closely approach the matches now in use, that we wonder the inventors did not succeed long since in contriving the very facile means of striking a light that we now enjoy. Phosphorus and brimstone matches were first employed for the purpose. The phosphorus was contained in a bottle placed within a tin case, which also held the pointed brimstone matches and a piece of cork. The match was dipped into the phosphorus bottle, and then rubbed on the cork; and the friction excited sufficient heat to inflame the small quantity of phosphorus adhering to the match and, to set fire to the sulphur. These phosphorus boxes answered the purpose very well, but the apprehended danger of using so inflammable a substance prevented their coming into general use; and they were much more costly than a tinder-box.

In the next advance, if it may be so called, in the invention of instantaneous light-producers, phosphorus was altogether discarded, and a mixture of chlorate of potass, then called oxymuriate of potass, and sugar was employed. Those substances, when combined, inflame explosively in contact with sulphuric acid. In applying them for the purpose of obtaining instantaneous light, they were mixed together in an adhesive menstruum, into which the ends of small rectangular matches were dipped. These matches very nearly resembled the "Lucifers" of the present day. To ignite them, a small bottle containing sulphuric acid and asbestos was provided, and they were arranged together in an ornamental taper-stand for the chimney-piece. This apparatus was not received with much favour, partly on account of injury done by a careless use of the sulphuric acid, partly because it failed to act when the acid had absorbed moisture from the atmosphere, but principally because of its cost.

To obviate the objection arising from the use of sulphuric acid in open bottles, an ingenious contrivance was adopted, by which each match contained its own reservoir of acid sufficient for igniting the inflammable compound. Small glass globules, containing sulphuric acid, were introduced into the composition of chlorate of potass and sugar, which, when broken, set fire to the mixture and lighted the match. These instantaneous lights, which were called _Prometheans_, were more ingenious than useful, because the trouble of manufacture rendered them expensive, and the sulphuric acid was more likely to injure furniture in that form than when a bottle with asbestos was used. The Prometheans, however, possessed the advantage of portability, and for occasional purposes they were convenient. In some of the forms in which the Prometheans were manufactured, the glass globule of acid, surrounded by its inflammable compound, was attached to the end of a small stick of sealing-wax, sufficiently large to seal a letter; but this refinement in instantaneous lights was not much patronized.

Notwithstanding these ingenious attempts to produce light by chemical action, the flint-and-steel retained possession of the field until a match was made that ignited by friction alone. The first kind of friction match was invented in 1832. It consisted of a thin splinter of dried wood, the top of which was dipped in a mixture of one part of chlorate of potass, two of sulphide of antimony, and one of gum. To ignite the match it was necessary to draw it briskly through sand-paper. These matches required some address to light them, because much more friction was required than is sufficient to light Lucifers.

The next improvement was the "Congreve" match, in which recourse was had to the materials previously used, separately, for obtaining instantaneous lights. Congreve matches were composed of an emulsion of phosphorus mixed with chlorate of potass, into which the matches, previously tipped with sulphur, were dipped. These matches were of the same size and form as the Lucifers now in general use, and they ignited readily by friction on sand-paper or other rough surface. Their explosive noise on inflammation, which gave them their name, was the only apparent difference between Congreves and Lucifers, and their introduction completely supplanted the flint-and-steel.

The noiseless match, or Lucifer, has, in its turn, driven the Congreve almost out of use, though for practical purposes the latter was as effective, and it was less dangerous. The Lucifer matches depend altogether on phosphorus for their inflammability. Their composition is an emulsion of phosphorus with glue, nitre, and some colouring matters. The sulphur matches, after having been tipped with that composition, are exposed in a warm room until a sufficient quantity of the phosphorus is evaporated by slow combustion, to leave a film of glue on the surface to protect the remainder from the action of the atmosphere. The usual proportions for the compound are, phosphorus four parts, nitre ten, glue six, red ochre five, and smalt two. The principle on which the action of Lucifer matches depends, is the strong affinity of phosphorus for oxygen, of which the nitre with which it is mixed contains an abundant supply; and by drawing the match across sand-paper, sufficient heat is excited by the friction to ignite the phosphorus, and the nitre supplies the oxygen to maintain rapid combustion.