Chapter 21

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If _c_ = weight of composition taken, _d_ = " " filter paper, _a_ = " after first extraction, _b_ = " " second extraction, then _c+d-a_ = weight of fulminate, _c+d-a-b_ = " " KClO_{3}, _b-d_ = " " sulphide of antimony.

The composition should be finely ground in an agate mortar.

The results of the a.n.a.lysis by this method of two mixtures of known composition are given below--

________________________________________________________________________ | | | | | | A | B | | | | | | | Percentage | Percentage | Percentage | Percentage | | | Taken. | Found. | Taken. | Found. | |____________________|____________|____________|____________|____________| | | | | | | | Antimony Sulphide | 36.47 | 36.25 | 37.34 | 37.22 | | Pota.s.sium Chlorate | 33.25 | 33.71 | 46.03 | 46.43 | | Mercury Fulminate | 30.27 | 30.02 | 16.61 | 16.34 | |____________________|____________|____________|____________|____________|

Dr. H.W. Brownsdon"s (_Jour. Soc. Chem. Ind._, xxiv., April 1905) process is as follows:--The cap composition is removed by squeezing the cap with pliers, while held over a porcelain basin of about 200 c.c. capacity, and removing the loosened foil and broken composition by means of a pointed wooden chip. Composition adhering to the sh.e.l.l or foil is loosened by alcohol, and washed into the dish by means of alcohol in a small wash bottle. The sh.e.l.l and foil are put to one side and subsequently weighed when dry. The composition in the dish is broken down quite fine with a flat-headed gla.s.s rod, and the alcohol evaporated on the water bath till the residue is moist, but not quite dry, 25 c.c. of water are then added, and the composition well stirred from the bottom. After the addition of 0.5 grm. of pure sodium, thiosulphate, the contents of the dish, is well stirred for two and a half minutes. One drop of methyl orange is then added, and the solution t.i.trated with N/20 sulphuric acid, which has been standardised against weighings of 0.05-0.1 grm. fulminate to which 25 c.c.

of water is added in a porcelain dish, then 0.5 grm. of thiosulphate, and after stirring for two and a half minutes, t.i.trated with N/20 sulphuric acid. The small amount of antimony sulphide present does not interfere with the recognition of the end point. After t.i.tration, the solution is filtered through a small 5-1/2 cm. filter paper, which retains the antimony sulphide. The filter paper containing the Sb_{2}S_{3} is well washed and then transferred to a large 6 by 1 test tube. Five c.c. of strong hydrochloric acid are added, and the contents of the tube boiled gently for a few seconds until the sulphide is dissolved and all the H_{2}S driven off or decomposed: 2-3 c.c. of a saturated solution of tartaric acid are added, and the contents of the tube washed into a 250 c.c. Erlenmeyer flask. The solution is then nearly neutralised with sodium carbonate, excess of bi-carbonate added, and after the addition of some starch solution t.i.trated with N/20 iodine solution. This method for small quant.i.ties of stibnite is both quick and accurate, the error being about 0.0003 grm. Sb_{2}S_{3} at the outside.

The tendency of this method is to give slightly low figures for the fulminate, but since these are uniform within a negligible error, it does not affect the value of the results as a criterion of uniformity. The following test results were obtained by Dr Brownsdon:--

____________________________________________________________ | | | | | Fulminate Taken. | Fulminate Found. | Error. | | Grm. | Grm. | Grm. | | | | | | 0.0086 | 0.0083 | -0.0003 | | 0.0082 | 0.0081 | -0.0001 | | 0.0074 | 0.0071 | -0.0003 | | 0.0068 | 0.0066 | -0.0002 | |____________________|___________________|___________________| | | | | | Stibnite Taken. |Sb_{2}S_{3}, Found.| Error. | | Grm. | Grm. | Grm. | | | | | | 0.0085 | 0.0084 | -0.0001 | | 0.0098 | 0.0099 | +0.0001 | | 0.0160 | 0.0157 | -0.0003 | | 0.0099 | 0.0100 | +0.0001 | |____________________|___________________|___________________|

TABLE FOR CORRECTION OF VOLUMES OF GASES FOR TEMPERATURE, GIVING THE DIVISOR FOR THE FORMULA.

V_{1} = V x B/(760 x (1 + dt)) (d = 0.003665) 1 + dt from 0 to 30 C.

___________________________________________________________ | | | | | t. | 760x(1+dt). | t. | 760x(1+dt). | t. | 760x(1+dt).

_____|_____________|_____|_____________|_____|_____________ | | | | | C. | | C. | | C. | 0.0 | 750.000 | 1.7 | 764.7352 | 3.4 | 769.4704 .1 | 760.2785 | .8 | 765.0137 | .5 | 769.7489 .2 | 760.5571 | .9 | 765.2923 | .6 | 770.0274 .3 | 760.8356 | 2.0 | 765.5708 | .7 | 770.3060 .4 | 761.1142 | .1 | 765.8493 | .8 | 770.5845 .5 | 761.3927 | .2 | 766.1279 | .9 | 770.8631 .6 | 761.6712 | .3 | 766.4064 | 4.0 | 771.1416 .7 | 761.9498 | .4 | 766.6850 | .1 | 771.4201 .8 | 762.2283 | .5 | 766.9635 | .2 | 771.6987 .9 | 762.5069 | .6 | 767.2420 | .3 | 771.9772 1.0 | 762.7854 | .7 | 767.5206 | .4 | 772.2558 .1 | 763.0639 | .8 | 767.7991 | .5 | 772.5343 .2 | 763.3425 | .9 | 768.0777 | .6 | 772.8128 .3 | 763.6210 | 3.0 | 768.3562 | .7 | 773.0914 .4 | 763.8996 | .1 | 768.6347 | .8 | 773.3699 .5 | 764.1781 | .2 | 768.9133 | .9 | 773.6485 .6 | 764.4566 | .3 | 769.1918 | 5.0 | 773.9270 _____|_____________|_____|_____________|_____|_____________ ___________________________________________________________ | | | | | t. | 760x(1+dt). | t. | 760x(1+dt). | t. | 760x(1+dt).

_____|_____________|_____|_____________|_____|_____________ | | | | | C. | | C. | | C. | 5.1 | 774.2055 | .9 | 787.5755 | .7 | 800.9454 .2 | 774.4841 |10.0 | 787.8540 | .8 | 801.2239 .3 | 774.7626 | .1 | 788.1325 | .9 | 801.5025 .4 | 775.0412 | .2 | 788.4111 |15.0 | 801.7810 .5 | 775.3197 | .3 | 788.6896 | .1 | 802.0595 .6 | 775.5982 | .4 | 788.9682 | .2 | 802.3381 .7 | 775.8768 | .5 | 789.2467 | .3 | 802.6166 .8 | 776.1553 | .6 | 789.5252 | .4 | 802.8952 .9 | 776.4339 | .7 | 789.8038 | .5 | 803.1737 6.0 | 776.7124 | .8 | 790.0823 | .6 | 803.4522 .1 | 776.9909 | .9 | 790.3609 | .7 | 803.7308 .2 | 777.2695 |11.0 | 790.6394 | .8 | 804.0093 .3 | 777.5480 | .1 | 790.9179 | .9 | 804.2879 .4 | 777.8266 | .2 | 791.1965 |16.0 | 804.5664 .5 | 778.1051 | .3 | 791.4750 | .1 | 804.8449 .6 | 778.3836 | .4 | 791.7536 | .2 | 805.1235 .7 | 778.6622 | .5 | 792.0321 | .3 | 805.4020 .8 | 778.9407 | .6 | 792.3106 | .4 | 805.6806 .9 | 779.2193 | .7 | 792.5892 | .5 | 805.9591 7.0 | 779.4978 | .8 | 792.8677 | .6 | 806.2376 .1 | 779.7763 | .9 | 793.1463 | .7 | 806.5162 .2 | 780.0549 |12.0 | 793.4248 | .8 | 806.7947 .3 | 780.3334 | .1 | 793.7033 | .9 | 807.0733 .4 | 780.6120 | .2 | 793.9819 |17.0 | 807.3518 .5 | 780.8905 | .3 | 794.2604 | .1 | 807.6303 .6 | 781.1690 | .4 | 794.5390 | .2 | 807.9089 .7 | 781.4476 | .5 | 794.8175 | .3 | 808.1874 .8 | 781.7261 | .6 | 795.0960 | .4 | 808.4660 .9 | 782.0047 | .7 | 795.3746 | .5 | 808.7445 8.0 | 782.2832 | .8 | 795.6531 | .6 | 809.0230 .1 | 782.5617 | .9 | 795.9317 | .7 | 809.3016 .2 | 782.8403 |13.0 | 796.2102 | .8 | 809.5801 .3 | 783.1188 | .1 | 796.4887 | .9 | 809.8587 .4 | 783.3974 | .2 | 796.7673 |18.0 | 810.1372 .5 | 783.6959 | .3 | 797.0458 | .1 | 810.4175 .6 | 783.9544 | .4 | 797.3244 | .2 | 810.6943 .7 | 784.2330 | .5 | 797.6029 | .3 | 810.9728 .8 | 784.5115 | .6 | 797.8814 | .4 | 811.2514 .9 | 784.7901 | .7 | 798.1600 | .5 | 811.5299 9.0 | 785.0686 | .8 | 798.4385 | .6 | 811.8084 .1 | 785.3471 | .9 | 798.7171 | .7 | 812.0870 .2 | 785.6257 |14.0 | 798.9956 | .8 | 812.3655 .3 | 785.9042 | .1 | 799.2741 | .9 | 812.6441 .4 | 786.1828 | .2 | 799.5527 |19.0 | 812.9226 .5 | 786.4613 | .3 | 799.8312 | .1 | 813.2011 .6 | 786.7398 | .4 | 800.1098 | .2 | 813.4797 .7 | 787.0184 | .5 | 800.3883 | .3 | 813.7582 .8 | 787.2969 | .6 | 800.6668 | .4 | 814.0368 _____|_____________|_____|_____________|_____|_____________ ___________________________________________________________ | | | | | t. | 760x(1+dt). | t. | 760x(1+dt). | t. | 760x(1+dt).

_____|_____________|_____|_____________|_____|_____________ | | | | | C. | | C. | | C. | 19.5 | 814.3153 |23.0 | 824.0642 | .5 | 833.8131 .6 | 814.5938 | .1 | 824.3427 | .6 | 834.0916 .7 | 814.8724 | .2 | 824.6213 | .7 | 834.3702 .8 | 815.1500 | .3 | 824.8998 | .8 | 834.6487 .9 | 815.4925 | .4 | 825.1784 | .9 | 834.9273 20.0 | 815.7080 | .5 | 825.4569 |27.0 | 835.2058 .1 | 815.9865 | .6 | 825.7354 | .1 | 835.4843 .2 | 816.2651 | .7 | 826.0140 | .2 | 835.7629 .3 | 816.5436 | .8 | 826.2925 | .3 | 836.0414 .4 | 816.8222 | .9 | 826.5711 | .4 | 836.3200 .5 | 817.1007 |24.0 | 826.8496 | .5 | 836.5985 .6 | 817.3792 | .1 | 827.1281 | .6 | 836.8770 .7 | 817.6578 | .2 | 827.4067 | .7 | 837.1556 .8 | 817.9363 | .3 | 827.6852 | .8 | 837.4341 .9 | 818.2149 | .4 | 827.9638 | .9 | 837.7127 21.0 | 818.4934 | .5 | 828.2423 |28.0 | 837.9912 .1 | 818.7719 | .6 | 828.5208 | .1 | 838.2697 .2 | 819.0505 | .7 | 828.7994 | .2 | 838.5483 .3 | 819.3290 | .8 | 829.0779 | .3 | 838.8268 .4 | 819.6076 | .9 | 829.3565 | .4 | 839.1054 .5 | 819.8861 |25.0 | 829.6350 | .5 | 839.3839 .6 | 820.1646 | .1 | 829.9135 | .6 | 839.6624 .7 | 820.4432 | .2 | 830.1921 | .7 | 839.9410 .8 | 820.7217 | .3 | 830.4706 | .8 | 840.2195 .9 | 821.0003 | .4 | 830.7492 | .9 | 840.4981 22.0 | 821.2788 | .5 | 831.0277 |29.0 | 840.7766 .1 | 821.5573 | .6 | 831.3062 | .1 | 841.0551 .2 | 821.8859 | .7 | 831.5848 | .2 | 841.3337 .3 | 822.1144 | .8 | 831.8633 | .3 | 841.6122 .4 | 822.3930 | .9 | 832.1419 | .4 | 841.8908 .5 | 822.6715 |26.0 | 832.4204 | .5 | 842.1693 .6 | 822.9500 | .1 | 832.6989 | .6 | 842.4478 .7 | 823.2286 | .2 | 832.9775 | .7 | 842.7264 .8 | 823.5071 | .3 | 833.2560 | .8 | 843.0049 .9 | 823.7857 | .4 | 833.5346 | .9 | 843.2835 | | | |30.0 | 843.5620 _____|_____________|_____|_____________|_____|_____________

CHAPTER VIII.

_FIRING POINT OF EXPLOSIVES, HEAT TESTS, &c._

Horsley"s Apparatus--Table of Firing points--The Government Heat-Test Apparatus for Dynamites--Nitro-Glycerine, Nitro-Cotton, and Smokeless Powders--Liquefaction and Exudation Tests--Page"s Regulator for Heat-Test Apparatus--Specific Gravities of Explosives--Table of Temperature of Detonation, Sensitiveness, &c.

~The Firing Point of Explosives.~--The firing point of an explosive may be determined as follows:--A copper dish, about 3 inches deep, and 6 or more wide, and fitted with a lid, also of copper, is required. The lid contains several small holes, into each of which is soldered a thick copper tube about 5 mm. in diameter, and 3 inches long, with a rather larger one in the centre in which to place a thermometer. The dish is filled with Rose"s metal, or paraffin, according to the probable temperature required. The firing point is then taken thus:--After putting a little piece of asbestos felt at the bottom of the centre tube, the thermometer is inserted, and a small quant.i.ty of the explosive to be tested is placed in the other holes; the lid is then placed on the dish containing the melted paraffin or metal, in such a way that the copper tubes dip below the surface of the liquid; the temperature of the bath is now raised until the explosive fires, and the temperature noted. The initial temperature should also be noted.

THE FIRING POINT OF VARIOUS EXPLOSIVES (by C. E. Munroe).

(Horsley"s Apparatus used.)

_____________________________________________________________________ | | C.

French gunpowder | 295 | " "

Rifle powder (picrate) | 358 | " "

Cannon | 380 | " "

__________________________________|_________|________________________

Horsley"s apparatus consists of an iron stand with a ring support, holding a hemispherical iron vessel or bath in which solid paraffin is put. Above this is another movable support, from which a thermometer is suspended, and so adjusted that its bulb is immersed in the material contained in the iron vessel. A thin copper cartridge-case, 5/8 inch in diameter and 1-15/16 inch long, is suspended over the bath by means of a triangle, so that the end of the case is just 1 inch below the surface of the molten material. On beginning the experiment of determining the firing point of any explosive, the material in the bath is heated to just above the melting point; the thermometer is inserted in it, and a minute quant.i.ty of the explosive is placed in the bottom of the cartridge-case. The initial temperature is noted, and then the cartridge-case containing the explosive is inserted in the bath. The temperature is quickly raised until the contents of the cartridge-case flash off or explode, when the temperature is noted as the _firing point_.

[Ill.u.s.tration: FIG. 46.--HEAT TEST APPARATUS.]

Professor C.E. Munroe, of the U.S. Torpedo Station, has determined the firing point of several explosives by means of this apparatus.

~The Government Heat Test (Explosives Act, 1875): Apparatus required.~--A water bath, consisting of a spherical copper vessel _(a)_, Fig. 46, of about 8 inches diameter, and with an aperture of about 5 inches; the bath is filled with water to within a quarter of an inch of the edge. It has a loose cover of sheet copper about 6 inches in diameter _(b)_ and rests on a tripod stand about 14 inches high _(c)_, which is covered with coa.r.s.e wire gauze _(e)_, and is surrounded with a screen of thin sheet copper _(d)_. Within the latter is placed an argand burner _(f)_ with gla.s.s chimney. The cover _(b)_ has four holes arranged, as seen in Fig. II., No.

4 to contain a Page"s[A] or Scheibler"s regulator, No. 3 the thermometer, Nos. 1 and 2 the test tubes containing the explosive to be tested. Around the holes 1 and 2 on the under side of the cover are soldered three pieces of bra.s.s wire with points slightly converging (Fig. III.); these act as springs, and allow the test tubes to be easily placed in position and removed.

[Footnote A: See _Chem. Soc. Jour._, 1876, i. 24. F.J.M. Page.]

~Test Tubes~, from 5-1/4 to 5-1/2 inches long, and of such a diameter that they will hold from 20 to 22 cubic centimetres of water when filled to a height of 5 inches; rather thick gla.s.s is preferable. Indiarubber stoppers, fitting the test tubes, and carrying an arrangement for holding the test papers, viz., a narrow gla.s.s tube pa.s.sing through the centre of the stopper, and terminating in a platinum wire hook. A gla.s.s rod drawn out and the end turned up to form a hook is better.

~The Thermometer~ should have a range from 30 to 212 F., or from 1 to 100 C. A minute clock is useful.

~Test Paper.~--The test paper is prepared as follows:--45 grains (2.9 grms.) of white maize starch (corn flour), previously washed with cold water, are added to 8-1/2 oz. of water. The mixture is stirred, heated to boiling, and kept gently boiling for ten minutes; 15 grains (1 grm.) of pure pota.s.sium iodide (previously recrystallised from alcohol, absolutely necessary) are dissolved in 8-1/2 oz. of distilled water. The two solutions are thoroughly mixed and allowed to get cold. Strips or sheets of white English filter paper, previously washed with water and re-dried, are dipped into the solution thus prepared, and allowed to remain in it for not less than ten seconds; they are then allowed to drain and dry in a place free from laboratory fumes and dust. The upper and lower margins of the strips or sheets are cut off, and the paper is preserved in well- stoppered or corked bottles, and in the dark. The dimensions of the pieces of test paper used are about 4/10 inch by 8/10 inch (10 mm. by 20 mm.).[A]

[Footnote A: When the paper is freshly prepared, and as long as it remains in good condition, a drop of diluted acetic acid put on the paper with a gla.s.s rod produces no coloration. In process of time it will become brownish, when treated with the acid, especially if it has been exposed to sunlight. It is then not fit for use.]

In Germany zinc-iodide starch paper is used, which is considered to be more sensitive than pota.s.sium iodide.

~Standard Tint Paper.~--A solution of caramel in water is made of such concentration that when diluted one hundred times (10 c.c. made up to 1 litre) the tint of this diluted solution equals the tint produced by the Nessler test in 100 c.c. water containing .000075 grm. of ammonia, or .00023505 grm. AmCl. With this caramel solution lines are drawn on strips of white filter paper (previously well washed with distilled water, to remove traces of bleaching matter, and dried) by means of a quill pen.

When the marks thus produced are dry, the paper is cut into pieces of the same size as the test paper previously described, in such a way that each piece has a brown line across it near the middle of its length, and only such strips are preserved in which the brown line has a breadth varying from 12 mm. to 1 mm. (1/50 of an inch to 1/25 of an inch).

~Testing Dynamite, Blasting Gelatine, and Gelatine Dynamite.~--Nitro- glycerine preparations, from which the nitro-glycerine can be extracted in the manner described below, must satisfy the following test, otherwise they will not be considered as manufactured with "thoroughly purified nitro-glycerine," viz., fifteen minutes at 160 F. (72 C.).

~Apparatus required.~--A funnel 2 inches across (_d_), a cylindrical measure divided into grains (_e_), Fig. 47.

~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 gla.s.s 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 pa.s.sed through, it must be removed from the nitro-glycerine by filter paper, or the nitro-glycerine may be filtered.

[Ill.u.s.tration: FIG. 47.--APPARATUS FOR SEPARATING THE NlTRO-GLYCERINE FROM DYNAMITE.]

[Ill.u.s.tration: 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 gla.s.s 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 gla.s.s 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 sc.r.a.ping, 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 s.p.a.ce 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 gla.s.s 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 pa.s.sed once through the mill, the first portion of material which pa.s.ses 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 pa.s.sed 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.

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-coa.r.s.e 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 h.o.r.n.y 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.]

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