~Mode of Operation.~—About 300 (19.4 grms.) to 400 grains (26 grms.) of dynamite (b), finely divided, are placed in the funnel, which is loosely plugged by freshly ignited asbestos (a). The surface is smoothed by means of a flat-headed glass rod or stopper, and some clean washed and dried kieselguhr (c) is spread over it to the depth of about 1/8 inch. Water is then poured on from a wash bottle, and when the first portion has been soaked up more is added; this is repeated until sufficient nitro- glycerine has collected in the graduated measure (e). If any water should have passed through, it must be removed from the nitro-glycerine by filter paper, or the nitro-glycerine may be filtered.
[Illustration: FIG. 47.—APPARATUS FOR SEPARATING THE NlTRO-GLYCERINE FROM
DYNAMITE.]
[Illustration: FIG. 48.—TEST TUBE ARRANGED FOR HEAT TEST.]
~Application of Test.~—The thermometer is fixed so as to be inserted through the lid of the water bath into the water, which is maintained at 160° F. (72° C.), to a depth of 2-3/4 inches. Fifty grains (= 3.29 grms.) of nitro-glycerine to be tested are weighed into the test tube, in such a way as not to soil the sides of the tube (use a pipette). A test paper is fixed on the hook of the glass rod, so that when inserted into the tube it will be in a vertical position. A sufficient amount of a mixture of half distilled water and half glycerine, to moisten the upper half of the paper, is now applied to the upper edge of the test paper by means of a glass rod or camel's hair pencil; the cork carrying the rod and paper is fixed into the test tube, and the position of the paper adjusted so that its lower edge is about half way down the tube; the latter is then inserted through one of the holes in the cover to such a depth that the lower margin of the moistened part of the paper is about 5/8 inch above the surface cover. The test is complete when the faint brown line, which after a time makes its appearance at the line of boundary between the dry and moist part of the paper, equals in tint the brown line of the standard tint paper.
~Blasting Gelatine, Gelatine Dynamite, Gelignite, &c.~—Fifty grains (= 3.29 grms.) of blasting gelatine are intimately mixed with 100 grains (= 6.5 grms.) of French chalk. This is done by carefully working the two materials together with a wooden pestle in a wooden mortar. The mixture is then gradually introduced into the test tube, with the aid of gentle tapping upon the table between the introduction of successive portions of the mixture into the tube, so that when the tube contains all the mixture it shall be filled to the extent of 1-3/4 inch of its height. The test paper is then inserted as above described for nitro-glycerine. The sample tested must stand a temperature of 160° F. for a period of ten minutes before producing a discoloration of the test paper corresponding in tint to the standard paper.
N.B.—Non-gelatinised nitro-glycerine preparations, from which the nitro-glycerine cannot be expelled by water, are tested without any previous separation of the ingredients, the temperature being as above 160° F., and the time being seven minutes.
~Gun-Cotton, Schultze Gunpowder, E.C. Powder, &c.: A. Compressed Gun- Cotton.~—Sufficient material to serve for two or more tests is removed from the centre of the cartridge by gentle scraping, and if necessary, further reduced by rubbing between the fingers. The fine powder thus produced is spread out in a thin layer upon a paper tray 6 inches by 4-1/2 inches, which is then placed inside a water oven, kept as nearly as possible at 120° F. (49° C.). The wire gauze shelves of the oven should be about 3 inches apart. The sample is allowed to remain at rest for fifteen minutes in the oven, the door of which is left wide open. After the lapse of fifteen minutes the tray is removed and exposed to the air of the room for two hours, the sample being at some point within that time rubbed upon the tray with the hand, in order to reduce it to a fine and uniform state of division.
The heat test is performed as before, except that the temperature of the bath is kept at 170° F. (66° C.), and regulator set to maintain that temperature. Twenty grains (1.296 grm.) are used, placed in the test tube, gently pressed down until it occupies a space of as nearly as possible 1-5/10 inch in the test tube of dimensions previously specified. The fine cotton adhering to the sides of the tube can be removed by a clean cloth or silk handkerchief. The paper is moistened by touching the upper edge with a drop of the 50 per cent. glycerine solution, the tube inserted in the bath to a depth of 2-1/2 inches, measured from the cover, the regulator and thermometer being inserted to the same depth. The test paper is to be kept near the top of the test tube, but clear of the cork, until the tube has been immersed for about five minutes. A ring of moisture will about this time be deposited upon the sides of the test tube, a little above the cover of the bath. The glass rod must then be lowered until the lower margin of the moistened part of the paper is on a level with the bottom of the ring of moisture in the tube. The paper is now closely watched, The test is complete when a very faint brown coloration makes its appearance at the line of boundary between the dry and moist parts of the paper. It must stand the test for not less than ten minutes at 170° F. (The time is reckoned from the first insertion of the tube in the bath until the appearance of a discoloration of the test paper.)
~B. Schultze Powder, E.C. Powder, Collodion-Cotton, &c.~—The sample is dried in the oven as above for fifteen minutes, and exposed for two hours to the air. The test as above for compressed gun-cotton is then applied.
~C. Cordite~ must stand a temperature of 180° F. for fifteen minutes. The sample is prepared as follows:—Pieces half an inch long are cut from one end of every stick selected for the test: in the case of the thicker cordites, each piece so cut is further subdivided into about four portions. These cut pieces are then passed once through the mill, the first portion of material which passes through being rejected on account of the possible presence of foreign matter from the mill. The ground material is put on the top sieve of the nest of sieves, and sifted. That portion which has passed through the top sieve and been stopped by the second is taken for the test. If the mill is properly set, the greater portion of the ground material will be of the proper size. If the volatile matter in the explosive exceeds 0.5 per cent., the sifted material should be dried at a temperature not exceeding 140° F, until the proportion does not exceed 0.5 per cent. After each sample has been ground, the mill must be taken to pieces and carefully cleaned. The sieves used consist of a nest of two sieves with holes drilled in sheet copper. The holes in the top sieve have a diameter = 14 B.W.G., those in the second = 21 B.W.G.