Chapter 3

The question concerning the origin of this organic substance or its combination with lime can only be answered in one way, viz., that it must have been washed by the rain water out of the paper. But since such a solid substance, easily soluble in water, is contained neither in the fresh roofing paper nor in the coal tar, the only deduction is that it must have arisen by the decomposition of the tar, in consequence of the operation of the oxygen. The lime comes from the coating substance of the roof, for which tar mixed with coal pitch was used. The latter was fused with carbonate of lime. These analyses furthermore show that the formation of the organic acid easily soluble in water depends upon the season; and that a larger quantity of it is generated in warm, sunny weather than in cold, without sunshine. This peculiarity of the solid, resinous constituents of the coal tar, to be by the operation of the atmospheric oxygen altered into such products that are readily soluble in water, makes the tar very unsuitable as a saturative substance for a roofing paper. How rapidly a paper roof can be ruined by the generation of this injurious organic acid will be seen from the following calculation: Let us suppose that an average of 132 gallons of rain water falls upon ten square feet roof surface per year, and that the arithmetical mean 0.932 of the largest (1.680) and smallest number (0.184) be the quantity of the soluble brown substance which on an average is dissolved in one quart of rain water; hence from ten square feet of roof surface are rinsed away with the rain water per year 466 grammes of the soluble decomposition products of the tar. The oxidation process will not always occur as intensely as by a paper roof, ten years old and painted two years ago, which instigated above described experiment. As long as the roofing paper is fresh and less porous, especially if the occurring pores are filled and closed again by repeated coatings, oxidation will take place far less rapidly. Besides this, the protective coating applied to the roof surface is exposed most to this oxidation process. Even by assuming this constantly progressive destructive action of the oxygen on the roofing paper to be much less than above stated, we can readily imagine that it must be quite large. If it is desired to produce a material free of faults, it is first of all indispensable that unobjectionable raw material be procured. Coal tar was formerly used almost exclusively for the coating of a roof. It was heated and applied hot upon the surface. In order to avoid the running off of the thinly fluid mass, the freshly coated surface was strewn with sand. The most volatile portion of the tar evaporated soon, whereby the coating became thicker and finally dried. The bad properties of the coal tar, pointed out elsewhere, made it very unsuitable even for this purpose, and experiments were instituted to compound mixtures, by adding other ingredients to the tar, that should more fully comply with its function. It may be said in general that the coating masses for roofs can be divided into two classes: either as lacquers or as cements. To the former may be classed those of a fairly thinly fluid consistency, and which contain volatile oils in such quantities that they will dry quickly. Cements are those of a thickly fluid consistency, and are rendered thus fluid by heating. It is not necessary that the coating applied should harden quickly, as it assumes soon after its application a firmness sufficient to prevent it from running off the roof. Coal tar is to be classed among lacquers. If it has been liberated by distillation from the volatile oils, it is made better suited for the purpose than the ordinary kind. The mass contains much more asphaltum, and after drying, which takes place soon, it leaves a far thicker layer upon the roof surface, while the pores, which had formed in the roofing paper consequent on drying, are better filled up. Nevertheless, the distilled tar also has retained the property of drying with time into a hard, vitreous mass, and ultimately to be destroyed by decomposition.--_The Roofer_.

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A PHYSICAL LABORATORY INDICATOR.

The difficulties attending the management of a physical laboratory are much greater than those of a chemical one. The cause of this lies in the fact that in the latter the apparatus is less complicated and the pieces less varied. Any contrivance that will reduce the labor and worry connected with the running of a laboratory is valuable.

A physical laboratory may be arranged in several ways. The apparatus may be kept in a store room and such as is needed may be given to the student each day and removed after the experiments are performed; or the apparatus for each experiment or system of experiments may be kept in a fixed place in the laboratory ready for assembling; for certain experiments the apparatus may be kept in a fixed place in the laboratory and permanently arranged for service.

Each student may have his own desk and apparatus or he may be required to pass from desk to desk. The latter method is preferable.

When a store room is used the services of a man are required to distribute and afterward to collect. If the apparatus is permanently distributed, a large room is necessary, but the labor of collecting and distributing is done away with.

There are certain general experiments intended to show the use of measuring instruments which all students must perform. To illustrate the use of the indicator I have selected an elementary class, although the instrument is equally applicable to all classes of experiments.

Having selected a suitable room, tables may be placed against the walls between the windows and at other convenient places. Shallow closets are built upon these tables against the wall; they have glass doors and are fitted with shelves properly spaced. A large number of light wooden boxes are prepared, numbered from one up to the limit of the storage capacity of the closets. A number corresponding to that upon the box is placed upon the shelf, so that each one after removal may be returned to its proper place without difficulty. On the front of the box is a label upon which is written the experiment to be performed or the name of the apparatus whose use is to be learned, references to various books, which may be found in the laboratory library, and the apparatus necessary for the experiment, which ought to be found in the box. If any parts of the apparatus are too large to be placed in the box, the label indicates by a number where it may be found in the storage case.

It is evident that, instead of the above arrangement, all the boxes can be stacked in piles in a general store room. The described arrangement is preferable, as it prevents confusion in collecting and distributing apparatus when the class is large.

_The Indicator_ (see figure).--Some device is evidently desirable to direct the work of a laboratory with the least trouble and friction possible. I have found that the old fashioned "peg board," formerly used in schools to record the demerits of scholars, modified as in the following description, leaves nothing to be desired.

The requirements of such an instrument are these: It must show the names of the members of the class; it must contain a full list of the experiments to be performed; it must refer the student to the book and page where information in reference to the experiments or apparatus may be found; it must show what experiments are to be performed by each student at a given time; it must give information as to the place in the laboratory where the apparatus is deposited; it must show to the instructor what experiments have been performed by each student; it must prevent the assignment of the same experiment to two students; it must enable the instructor to assign the same experiment to two or more students; it must form a complete record of what has been done, what work is incomplete, and what experiments have not yet been assigned; it must also be so arranged that new experiments or sets of experiments may be exhibited.

+------+---+---+---+---+---+---+---+---+ | | A | B | C | D | E | F | G | H | +------+---+---+---+---+---+---+---+---+ | 1 | * o o * o o o o | | 2 | * o * * o o o o | | 3 | + * * * o o o o | | 4 | + o * * o o o o | | 5 | o + * * * * o o | | 6 | o + * * o * o o | | 7 | o o + * o o o o | | 8 | o o o + * o o o | | 9 | o o o * + o o o | | 10 | o o o o o + o o | | 11 | o o o * o o + * | | 12 | o o * * o + + + | | 13 | o o * o o o o o | | 14 | o o * o o o o o | | 15 | o o + o o o o o | | 16 | o o + + * o o * | +--------------------------------------+

A, B, C, etc., are cards upon which are the names of students. 1, 2, 3, etc., are cards like the one described in the article. The small circles (o) represent unassigned experiments. The black circles (*) (slate nails) represent work done. The caudate circles (+) (brass nail) represent work assigned.

The indicator consists of a plank of any convenient length and breadth. The front surface is divided into squares of such size that the pegs may be introduced and withdrawn with ease. At each corner of the squares holes are bored into which nails may be placed. There is a blank border at the top and another on the left side. At the top of each vertical column of holes is placed a card holder. This is made of light tin turned up on the long edges--which are vertical--and tacked to the board. Opposite each horizontal row of holes is a similar tin card holder, but of greater length, and having its length horizontal. The holders at the top of the board contain cards upon which the names of the class are written.

Cards, like the following, are prepared for the horizontal holders.

Stewart & Gee 229 Physical Manip. 85 Intensity of Gravity--Borda's Method 39 Glazebrook & Shaw 132 --------------------------------------------------------------

These cards are numbered from one to any desired number and are arranged in the holders consecutively.

Two kinds of nails are provided to fit the holes in the board: An ordinary slate nail and a common picture frame nail with a brass head. The latter indicates work to be done, the former work done.

To prepare the board for service, brass headed nails are placed opposite each experiment, and below the names, care being taken not to have more than one nail in the same horizontal row, unless it is intended that two persons or more are to work upon the same experiment.

There will be no conflict when the brass nails occupy diagonal lines. If they do not, a glance will show the fact.

After an experiment has been performed and a report made upon the usual blank, the brass nail is removed and a slate nail put in its place.

The board will show by the slate nails what work has been done by each student, by the brass nails what is yet to be done, and by the empty holes, experiments which have been omitted or are yet to be assigned. A slate nail opposite an experiment card indicates that that experiment may now be assigned to another person.

It is evident that the schedule for a whole term may be arranged in a few minutes and that the daily changes require very little time.

The board is hung in a convenient place. The student as he enters the laboratory looks for his name on the upper cards and under it for the first brass nail in the vertical column: to the left he finds the experiment card. On the left hand end of the slip he sees the book references, on the right hand end a number--39 in the sample card given above. Knowing the number, he proceeds to a desk and finds a box numbered in the same manner. He removes the box from the closet. On the label of the box is a list of all the apparatus necessary, which he will find in the box; the label also contains the book references. He performs the experiment, fills up a blank which he gives to the instructor, puts all the materials back in the box, replaces the box in its proper place in the closet and proceeds with the next experiment. With this indicator there is no difficulty in managing fifty students or more.

Comparatively little apparatus need be duplicated. Where apparatus is fixed against a wall a number may be tacked upon the wall and a card containing the information desired. The procedure is then the same as with the boxes. The cards on the board being removable, other ones may be inserted containing information in reference to other boxes having the same number but containing different materials. There can be no successful tampering with the board, for the record of experiments performed is upon the blanks which the students turn in and also in the individual note books which are written up and given to the instructor for daily examination.

Lafayette College. J.W. MOORE.

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NEW METHOD OF EXTINGUISHING FIRES

This is by George Dickson, of Toronto, Canada, and David Alanson Jones.

A mixture of water and liquefied carbon dioxide upon being discharged through pipes at high pressure causes the rapid expansion of the gas and converts the mixture into spray more or less frozen, and portions of the liquid carbon dioxide are frozen, owing to its rapid expansion, and are thus thrown upon the fire in a solid state, where said frozen carbon dioxide in its further expansion not only acts to put out the fire, but cools the surface upon which it falls, and thus tends to prevent reignition.

A represents a receptacle sufficiently strong to stand a pressure of not less than a thousand pounds to the square inch.

B B water receptacles.

In the drawings we have shown two receptacles B and only one receptacle A; but we do not wish to confine ourselves to any particular number, nor do we wish to confine ourselves to the horizontal position in which the receptacles are shown.

C is a pipe leading from the receptacle A to a point at or near the bottom of the receptacle B.

F is a pipe through which the mixture of water and liquefied gas from the receptacle B is forced by the expansion of said liquefied gas, the said pipe taking the mixture of water and liquefied gas from the bottom of the receptacle.

To use the apparatus, open the stop cock D in the pipe C, leading to one of the receptacles B, whereupon, owing to the lower pressure in the cylinder B, the liquid carbon dioxide expands and rises to the top of the cylinder A and forces the liquid carbon dioxide into the cylinder B, the same as the superior steam of a boiler forces the water of the boiler out when the same is tapped below the surface of the liquid. Now upon opening the tap H, this superior gas forces out the mixture of water and liquid carbon dioxide, which suddenly expanding causes portions of the globules of liquefied gas to be frozen, and these, being protected by a rapidly evaporating portion of the liquefied gas, are thrown on the fire in solid particles. At the same time the water is blown into a spray, which is more or less frozen. The fire is thus rapidly extinguished by the vaporization of the carbon dioxide and water spray.

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SMOKELESS GUNPOWDER.

BY HUDSON MAXIM.

During the last forty years leading chemists have continued to experiment with a view to the production of a gunpowder which should be smokeless. But not until the last few years has any considerable degree of success been attained.

To be smokeless, a gunpowder must yield only gaseous products of combustion. None of the so-called smokeless powders are entirely smokeless, although some of them are very nearly so.

The smoke of common black gunpowder is largely due to minute particles of solid matter which float in the air. About one-half of the total products of combustion of black gunpowder of ordinary composition consists of potassium carbonate in a finely divided condition and of potassium sulphate, which is produced chiefly by the burning in the air of potassium sulphide, another production of combustion, as on the outrushing gases it is borne into the air in a fine state of division.

Another cause for the smoke of gunpowder is the formation of small liquid vesicles which condense from some of the products of combustion thrown into the air in a state of vapor, in the same manner as vesicles of aqueous vapor form in the air on the escape of highly heated steam from the whistle of a locomotive.

Broadly speaking, an explosive compound is one which contains, within itself, all the elements necessary for its complete combustion, and whose heated gaseous products occupy vastly more space than the original compound. Such compound usually consists of oxygen, associated with other elements, for which it has great affinity, and from which it is held from more intimate union, or direct chemical combination, under normal conditions, by being in combination as well with other elements for which it has less affinity, but which it readily gives up for the stronger affinities when explosion takes place, the other elements either combining with one another to form new compounds or being set free in an uncombined state.

An explosive is said to detonate when the above changes take place instantaneously, the action being transmitted with the speed of electricity by a sort of molecular rhythm from molecule to molecule throughout the entire substance of the compound.

An explosive is said to explode when the above changes do not occur instantaneously throughout the whole substance, but whose combustion takes place from the surface inward of the particles or grains of which it is composed, thus requiring some definite lapse of time.

The elements of an explosive compound may be associated chemically as in nitro-glycerine and gun-cotton, which are chemical compounds, being the results of definite reactions. Or, an explosive may be a mere mechanical mixture of different substances comprising the necessary elements, as is ordinary black gunpowder, which is a compound of charcoal, sulphur and saltpeter, the saltpeter supplying the necessary oxygen.

No gunpowder can be smokeless in which saltpeter or any oxygen-bearing salt having a metallic base is employed, for when the salt gives up its oxygen, the base combines with other elements to produce a sulphate, a carbonate, or other salt, which, being solid, produces smoke. Therefore, to be smokeless, a gunpowder must contain no other elements than oxygen, hydrogen, nitrogen, and carbon, and in such proportions that the products of combustion shall be wholly gaseous. The nitric ethers--gun-cotton and nitro-glycerine--constitute such explosive compounds. These substances were formerly thought to be nitro-substitution compounds, but are now known to belong to the compound ethers of nitric acid.

Gun-cotton, discovered by Schonbein, in 1845, has since been looked upon as the most promising material for a smokeless gunpowder, it being a very powerful explosive and burning with practically no smoke. To-day, gun-cotton, in some form or other, constitutes the base of substantially all of the smokeless powders with which have been attained any considerable degree of success.

Gun-cotton alone and in its fibrous state has been found to be too quick, or violent, for propulsive purposes, such as use in firearms; as under such conditions of confinement it is very likely to detonate and burst the gun. However, if gun-cotton be dissolved in a suitable solvent, which is capable of being evaporated out, such as acetone, or acetate of ethyl, which are very volatile, it becomes, when thus dissolved and dried, a very hard, horn-like, amorphous substance, which may be used for a smokeless gunpowder. But this substance taken alone is very difficult to mould or granulate, and the loss of expensive solvents must necessarily be quite considerable.

When gun-cotton is reduced to a collodial solid, as above, and used as a smokeless gunpowder, the grains must be made comparatively small to insure prompt and certain ignition, and consequently the pressures developed in the gun are apt to be too great when charges sufficiently large are used to give desired velocities.

If, however, a compound be made of gun-cotton and nitro-glycerine, in about equal parts, by means of a volatile solvent or combining agent, such as one of the before mentioned, and the solvent evaporated out, we obtain practically a new substance and one which, as regards its explosive nature, is quite unlike either of its two constituents taken alone. The nitro-glycerine, furthermore, being itself a solvent of gun-cotton, much less of the volatile ether is necessary to render the compound of an amorphous character. Being quite plastic this substance may be wrought or moulded into any desired size or form of grain.

This simple compound of nitro-glycerine and gun-cotton, or with some slight modifications, has been found, when properly granulated, to be the most smokeless powder that has yet been discovered or invented. If pure chemicals are employed in the manufacture, and the gun-cotton and nitro-glycerine be made of the highest nitration and best quality, we have a smokeless powder which will possess the following desirable qualities:

1st. It is absolutely smokeless, that is, its products of combustion are entirely gaseous.

2d. Its products of combustion are in no way deleterious or unpleasant.

3d. It is perfectly safe to manufacture, handle and transport. There is no more danger of its exploding accidentally than there would be of an explosion of shavings or sawdust; for, unless well confined and set off with a strong primer, it will not explode at all. In the open its combustion is so slow as to in no way resemble or partake of the nature of an explosion.

4th. It is perfectly stable, and will keep any length of time absolutely without undergoing any change whatever, under all conditions of temperature or exposure to which gunpowder would ever be subjected.

5th. It is not hygroscopic, and may be soaked in water without being at all affected by it.

6th. It will not corrode the cartridge case.

7th. It will not foul the gun.

8th. It is sure of ignition with a good primer, and may be made to burn as slowly as desired by varying the character and size of the grains. Indeed, it may be made to burn so slowly as to fail of complete combustion before the bullet leaves the gun, and after firing several rounds, partly burned pieces of the powder may be picked up in front of the gun.

9th. In a shoulder arm, a velocity of 2,000 feet per second may be imparted to the bullet with this powder, and with a pressure in the chamber of the gun of not more than fifteen English tons. This is, of course, when the gun, cartridge case, primer, and projectile are adapted to the use of smokeless powder, and the granulation of the powder is adapted to them.