The camphor contained in this substance was, however, found to be a disadvantage, and its use discontinued.  The composition is now 50 per cent. of soluble nitro-cotton and 50 per cent. of nitro-glycerine.  As nitro-glycerine will not dissolve its own weight of nitro-cotton (even the soluble variety), benzol is used as a solvent, but is afterwards removed from the finished product, just as the acetone is removed from cordite.  About 1 per cent. of diphenylamine is added for the purpose of increasing its stability.

The colour of ballistite is a darkish brown.  It burns in layers when ignited, and emits sparks.  The size of the cubes into which it is cut is a 0.2-inch cube.  Its density is 1.6.  It is also, by means of a special machine, prepared in the form of sheets, after being mixed in a wooden trough fitted with double zinc plates, and subjected to the heating process by means of hot-water pipes.  It is passed between hot rollers, and rolled into sheets, which are afterwards put through a cutting machine and granulated.  Sir A. Nobel’s experiments[A] with this powder gave the following results:—­The charge used was 5 lbs. 8 oz., the size of the cubes being 0.2 inch.  The mean crusher-gauge pressure was 14.3 tons per square inch (maximum, 2,210; minimum, 2,142), and average pressure 2,180 atmospheres.  The muzzle velocity was 2,140 foot seconds, and the muzzle energy 1,429 foot tons.  A gramme of ballistite generates 615 c.c. of permanent gases, and gives rise to 1,365 grm. units of heat.  Ballistite is manufactured at Ardeer in Scotland, at Chilworth in Surrey, and also in Italy, under the name of Filite, which is in the form of cords instead of cubes.  The ballistite made in Germany contained more nitro-cellulose, and the finished powder was coated with graphite.  Its use has been discontinued as the Service powder in Germany, but it is still the Service powder in Italy.

[Footnote A:  Proc.  Roy.  Soc., vol. lii., p. 315.]

U.S.  Naval Smokeless Powder.—­This powder is manufactured at the U.S.  Naval Torpedo Station for use in guns of all calibres in the U.S.  Navy.  It is a nitro-cellulose powder, a mixture of insoluble and soluble nitro-cellulose together with the nitrates of barium and potassium, and a small percentage of calcium carbonate.  The proportions in the case of the powder for the 6-inch rapid-fire gun are as follows:—­Mixed nitro-cellulose (soluble and insoluble) 80 parts, barium nitrate 15 parts, potassium nitrate 4 parts, and calcium carbonate 1 part.  The percentage of nitrogen contained in the insoluble nitro-cellulose must be 13.30+-0.15, and in the soluble 11.60+-0.15, and the mean nitration strength of the mixture must be 12.75 per cent. of nitrogen.  The solvent used in making the powder is a mixture of ether (sp. gr. 0.720) 2 parts, and alcohol (95 per cent. by volume) 1 part.  The process of manufacture is briefly as follows:[A]—­The soluble and insoluble nitro-cellulose are dried separately