If too hard for the mill, the cordite may be softened by exposure to the vapour of acetone,[A] or reduced, to the necessary degree of subdivision by means of a sharp moderately-coarse rasp. Should it have become too soft in the acetone vapour for the mill, it should be cut up into small pieces, which may be brought to any desired degree of hardness by simple exposure to air. Explosives which consist partly of gelatinised collodion-cotton, and partly of ungelatinised gun-cotton, are best reduced to powder by a rasp, or softened by exposure to mixed ether and alcohol vapour at a temperature of 40° F. to 100° F.
[Footnote A: Mr W. Cullen (Jour. Soc. Chem. Ind., Jan. 31, 1901) says:— "Undoubtedly the advent of the horny smokeless powders of modern times has made it a little difficult to give the test the same scope as it had when first introduced." As a rule a simple explanation can be found for every apparently abnormal result, and in the accidental retention of a portion of the solvent used in the manufacture, will frequently be found an explanation of the trouble experienced.]
~Ballistite.~—In the case of ballistite the treatment is the same, except that when it is in a very finely granulated condition it need not be cut up.
~Guttmann's Heat Test.~—This test was proposed by Mr Oscar Guttmann in a paper read before the Society of Chemical Industry (vol. xvi., 1897), in the place of the potassium iodide starch paper used in the Abel test. The filter paper used is wetted with a solution of diphenylamine[A] in sulphuric acid. The solution is prepared as follows:—Take 0.100 grm. of diphenylamine crystals, put them in a wide-necked flask with a ground stopper, add 50 c.c. of dilute sulphuric acid (10 c.c. of concentrated sulphuric acid to 40 c.c. of water), and put the flask in a water bath at between 50° and 55° C. At this temperature the diphenylamine will melt, and at once dissolve in the sulphuric acid, when the flask should be taken out, well shaken, and allowed to cool. After cooling, add 50 c.c. of Price's double distilled glycerine, shake well, and keep the solution in a dark place. The test has to be applied in the following way:—The explosives that have to be tested are finely subdivided, gun-cotton, nitro-glycerine, dynamite, blasting gelatine, &c., in the same way as at present directed by the Home Office regulations. Smokeless powders are all to be ground in a bell-shaped coffee mill as finely as possible, and sifted as hitherto. 1.5 grm. of the explosive (from the second sieve in the case of smokeless powder) is to be weighed off and put into a test tube as hitherto used. Strips of well-washed filter paper, 25 mm. wide, are to be hung on a hooked glass rod as usual. A drop of the diphenylamine solution is taken up by means of a clean glass rod, and the upper corners of the filter paper are touched with it, so that when the two drops run together about a quarter of the filter paper is moist. This is then put into the test tube, and this again into the water bath, which has been heated to 70° C. The heat test reaction should not show in a shorter time than fifteen minutes. It will begin by the moist part of the paper acquiring a greenish yellow colour, and from this moment the paper should be carefully watched. After one or two minutes a dark blue mark will suddenly appear on the dividing line between the wet and dry part of the filter paper, and this is the point that should be taken.
[Footnote A: Dr G. Spica (Rivista, Aug. 1897) proposes to use hydrochloride of meta-phenylenediamine.]
~Exudation and Liquefaction Test for Blasting Gelatine, Gelatine Dynamite, &c.~—A cylinder of blasting gelatine, &c., is to be cut from the cartridge to be tested, the length of the cylinder to be equal to its diameter, and the ends being cut flat. The cylinder is to be placed on end on a flat surface without any wrapper, and secured by a pin passing vertically through its centre. In this condition the cylinder is to be exposed for 144 consecutive hours (six days and nights) to a temperature ranging from 85° to 90° F. (inclusive), and during such exposure the cylinder shall not diminish in height by more than one-fourth of its original height, and the upper cut surface shall retain its flatness and the sharpness of its edge.
~Exudation Test.~—There shall be no separation from the general mass of the blasting gelatine or gelatine dynamite of a substance of less consistency than the bulk of the remaining portion of the material under any conditions of storage, transport, or use, or when the material is subjected three times in succession to alternate freezing and thawing, or when subjected to the liquefaction test before described.
~Picric Acid.~—The material shall contain not more than 0.3 part of mineral or non-combustible matter in 100 parts by weight of the material dried at 160° F. It should not contain more than a minute trace of lead. One hundred parts of the dry material shall not contain more than 0.3 part of total (free and combined) sulphuric acid, of which not more than 0.1 part shall be free sulphuric acid. Its melting point should be between 248° and 253° F.
~Ammonite, Bellite, Roburite, and Explosives of similar Composition.~— These are required to stand the same heat test as compressed nitro-cellulose, gun-cotton, &c.
~Chlorate Mixtures.~—The material must not be too sensitive, and must show no tendency to increase in sensitiveness in keeping. It must contain nothing liable to reduce the chlorate. Chlorides calculated as potassium chloride must not exceed 0.25 per cent. The material must contain no free acid, or substance liable to produce free acid. Explosives of this class containing nitro-compounds will be subject to the heat test.