[Illustration: Fig. 53.—Service Guncotton for Cordite made at a Private
Factory.]

Readings are taken thirty minutes from the time the nitro-cellulose is heated, and are taken at intervals of fifteen minutes for about four hours; fresh caustic potash is added every thirty minutes or so. It is convenient to plot the results in curves. The curves given in Fig. 53 are from gun-cotton manufacturers in England at a private factory. The rate of evolution of nitrogen is as follows:—

In 1 hour. In 2 hours. In 3 hours. In 4 hours. N. N. N. N. in milligrammes. 1.25 2.55 4.5 5.75 1.5 3.25 5.25 6.75 These results are very satisfactory, the gun-cotton was of a very good quality. Several hours are necessary to remove all the air from the apparatus. Dr Will stated fifteen minutes in his original paper, but this has not been found sufficient. It has not been satisfactorily proved that Will's test can be applied to gelatinised nitro-cellulose powders. It is convenient to plot the results in curves; the nitrogen is generally given in cubic centimetres or in milligrammes, and readings taken every fifteen minutes. The steepness of the curve is a measure of the stability of the nitro-cellulose which is being examined. The steeper the curve the more nitrogen is evolved per unit of time, and the less stable the nitro- cellulose. In the case of unstable nitro-celluloses heated under the conditions described, the separation of nitrogen is much greater at first than at a later period. If the nitro-cellulose be very unstable, explosions are produced. If the separation of nitrogen is uniform during the prolonged heating, then the nitro-cellulose may be regarded as "normal." If it be desired to determine the absolute amount of nitrogen separated from a nitro-cellulose, the following conditions must be observed:—(1.) Accurate weighing of the nitro-cellulose; (2.) Determination of the amount of air in the CO_{2}, and deduction of this from the volume of gas obtained; (3.) Reduction of the volume of the gas to the volume at 0° C. and 760 mm. pressure.[A]

[Footnote A: See also Jour. Soc. Chem. Ind., Dec. 1902, pages 1545-1555, on the "Stability of Nitro-cellulose" and "Examination of Nitro- cellulose," Dr Will.]

~Bergrnann and Junk~[A] describe a test for nitro-cellulose that has been in use in the Prussian testing station for some years. The apparatus consists of a closed copper bath provided with a condenser and 10 countersunk tubes of 20 cm. length. By boiling amyl-alcohol in the bath, the tubes can be kept at a constant temperature of 132° C. The explosive to be tested is placed in a glass tube 35 cm. long and 2 cm. wide, having a ground neck into which an absorption bulb is fitted. The whole apparatus is surrounded by a shield, in case of explosion. In carrying out the test, 2 grms. of the explosive are placed in the glass tube and well pressed down. The absorption bulb is half filled with water, and fitted into the ground neck of the glass tube, which is then placed in one of the tubes in the bath previously brought to the boiling point (132° C.). The evolved oxides of nitrogen are absorbed in the water in the bulb, and at the end of two hours the tubes are removed from the bath, and on cooling, the water from the bulb flows back and wets the explosive. The contents of the tube are filtered and washed, the filtrate is oxidised with permanganate, and the nitrogen determined as nitric oxide by the Schultze-Tieman method. The authors conclude that a stable gun-cotton does not evolve more than 2.5 c.c. of nitric oxide per grm. on being heated to 132° C. for two hours, and a stable collodion-cotton not more than 2 c.c. under the same conditions. The percentage of moisture in the sample to be tested should be kept as low as possible. A sample of nitro-cellulose containing 1.97% of moisture gave an evolution of 2.6 c.c. per grm., while the same sample with 3.4% moisture gave an evolution of over 50 c.c. per grm. Sodium carbonate added to an unstable nitro-cellulose diminishes the rate of decomposition, but if sodium carbonate be intimately mixed with a stable nitro-cellulose the rate of decomposition will be increased. Calcium carbonate and mercury chloride have no influence. If an unstable nitro- cellulose be extracted with alcohol a stable compound is produced. The percentage solubility of a nitro-cellulose in ether-alcohol rises on heating to 132° C. A sample which before heating had a solubility of 4.7% had its solubility increased to 82.5% after six hours' heating.

[Footnote A: Jour. Soc. Chem. Ind., xxiii., Oct. 15, 1904, p. 953.]

Mr A.P. Sy (Jour. Amer. Chem. Soc., 1903) describes a new stability test for nitro-cellulose which he terms "The Elastic Limit of Powder Resistance to Heat." The test consists in heating the powder on a watch glass in an oven to a temperature of 115° C., after eight hours the watch glass and powder are weighed and the process repeated daily for six days or less. He claims that the powder is tested in its natural state, all the products of decomposition are taken into account, whilst in the old tests only the acid products are shown, and in the Will test only nitrogen, that it affords an indication of the effect of small quantities of added substances or foreign matters on the stability and that it is simple, and not subject to the variations of the old tests.

Obermüller (Jour. Soc. Chem. Ind., April 15, 1905) considers Bergmann and Junk's test is too complicated and occupies too much time; he proposes to heat gun-cotton to 140° C. in vacuo, and to measure continuously by means of a mercury manometer the pressure exerted by the evolved gases, the latter being maintained at constant volume; the rate at which the pressure increases is a measure of the rate of decomposition of the nitro- cellulose.

SPECIFIC GRAVITIES OF EXPLOSIVES, &C.

Nitro-glycerine 1.6
Gun-cotton (dry) 1.06
" (25 per cent. water) 1.32
Dynamite No. 1 1.62
Blasting gelatine 1.54
Gelatine dynamite 1.55
Ballistite 1.6
Forcite 1.51
Tonite 1.28
Roburite 1.40
Bellite 1.2-1.4
Carbo-dynamite 1.5
Turpin's cast picric acid 1.6
Nitro-mannite 1.6
Nitro-starch 1.5
Emmensite 1.8
Mono-nitro-benzene 1.2
Meta-di-nitro-benzene 1.575 at 18° C.
Ortho-di-nitro-benzene 1.590 "
Para-di-nitro-benzene 1.625 "
British gunpowder, E.X.E. 1.80
" " S.B.C. 1.85
Cannonite (powder) 1.60
Celluloid 1.35
Cellulose 1.45
Ammonium nitrate 1.707
Mercury fulminate 4.42