Gun cotton and nitric paper, according to tbe analysis of Messrs. Pelouze, Payen, and Poinsot, can be considered as formed of two equivalents of cellulose which have lost three equivalents of water by combining with five equivalents of nitric acid, constituting a double compound: -

Cl2H8083N05 CI2H808H02N05

Pyroxyrle C2IHI70I75N05

This compound, as we have seen, can be completely transformed into a gas at the temperature which inflames it, that is, from 347° to 356°; the oxygen of the acid burning all the carbon of the organic matter. It forms in 10 volume, 46 of oxide of carbon, 2 of carbonic acid, 10 of nitrogen, and 34 of vapor of water.* Some more complex and variable products are probably generated, but in all cases it does not deposit carbon or acid in the guns when the raw material is pure cotton, when the acids employed are perfectly free from foreign matters, and when the product has been purified of all free acids by washings.

Pure gun cotton is insoluble in water, alcohol, ether; soluble in the latter with the addition of a few hundredths of alcohol, soluble in weak proportions (1/2 to 2 per cent.) of acetic ether. Five times more soluble when prepared with nitric acid containing nitrous acid. + In this last case, the cotton is more or less disaggregated, and more slowly combustible. Gun cotton has some other properties which possess but little interest, but it is important to observe that under the same denomination of pyroxyle or pyroxyline they confound products with very different properties of explosibility, while containing the same elementary principles in equal proportions; and a remarkable thing is that those which explode at the lower temperature, present the weakest ballistic power, and have the most destructive action on firearms, by the vapor of hyponitric acid they generate.

* Mr. Combes has avoided the formation of oxide of carbon, a deleterious gas, and substituted it by carbonic acid, by adding to the pyroxyle the eight-tenths of its weight of chlorate of potash.

+ This acid is prepared by passing nitrous acid gas into the mixture until the total weight has increased from 1 1/2 to 2 per cent.

The causes of these great differences exist in the different degrees of cohesion of the organic substances employed. Thus, the cotton having a uniform cohesion, offering the maximum of surface to the action of the acid for the propagation of combustion, gives, when pure, the best product - the only one it is safe to use for firearms. The cotton from old cloth, old hemp, linen, and paper, which offer the most variation in their thickness, and in the alteration of the fibre which composes it, are sometimes inflammable at a lower temperature. Thus the thick nitric paper, newly prepared, and being a little acid after the washing, detonates at 212°. It is the product which has burst the most fire-arms, and sent the projec-tile the shortest distance, for the reason that its decomposition begins in the gun at a lower temperature, disengages at first vapors of hy-ponitric acid, and sometimes terminates immediately.

The pyroxam (nitric starch), more inflammable from 203° to 212° is so instable when completely saturated with nitric acid, that it is spontaneously decomposed at the ordinary temperature, giving abundant nitrous vapors, and even producing a detonation.

The pyroxam alters more rapidly in damp air, the disengagement of the gases raises the mass which becomes pasty, then syrupy, and gradually more acid and soluble in water; when dried it is not explosive, and dissolves in large proportions in anhydrous alcohol.

The different pyroxylic products are so much less stable, that they contain an excess of acid, on account of an insufficient washing.

Thus, the maximum of instability is met in the product (nitric starch) of which the organic basis has the least cohesion, and of which the aggregation is the most irregular, and each concentric bed of all the granules possesses several degrees of cohesion; indeed, the nitric starch, dissolves in its weight of acetic ether, and reduces by evaporation into diaphanous lamella, the cohesion of which is homogeneous. It is stable in the air, and docs not inflame at 212°. The same ether dissolves only 3/100 of its weight of nitric paper.

The preparation of nitric cotton is very simple, but requires many precautions, principally if the operation is with large quantities.

Prepare beforehand, in order to have it cold, a mixture of mono-hydrated nitric acid, 1 equivalent, 63, with 1 equivalent of concentrated sulphuric acid, 49. The liquid ought to present a sufficient volume to immerse in it all the cotton. If a certain quantity of the cotton impregnated with acid is left out of the mixture, the combination heats the fibre to the point of decomposing the nitric acid, and disengages nitrous vapors dangerous to breathe. It will even occasion a deflagration.

After 15 or 20 minutes, withdraw the cotton, press it well between glass, and wash it in a large excess of water. Press it and wash it in new water until it is no longer acid, to be sure of which, wash it with a very weak solution of carbonate of soda, and terminate by a washing with pure cold water. Press the cotton well and dry it. This cotton can be used immediately to load fire-arms; but it is better after a few days. One hundred parts produced from 170 to 175 parts of pyroxyle.

The preparation of the paper is the same as the cotton; but requires more care to avoid spoiling the sheets.

To obtain the pyroxam (nitric starch), the composition of which is similar to that of the cotton, dry the starch in vacuum at 257°, to evaporate the hydratation water. Leave the fecula to dry in a cool and dry place; dilute it in fifteen times its weight of the mixture of nitric and sulphuric acid. Leave to stand for six hours; wash it in an excess of water, and dry in a current of air at 104°. The pyroxyle can be decomposed, so as to set free the cellulose with all its chemical properties by the following process: Dip the pyroxyle in a concentrated boiling solution of chloride of iron. The deoxidizing action of this compound takes off the oxygen from the nitric acid, disengages hyponitric acid, and the cotton is covered with rust. This incrustation is taken up by diluted hydrochloric acid, and the cellulose is regenerated with all its primitive properties.

In the chapter on the application of gun cotton, we shall give another process of prepa-ration.