The nitro-glycerine is best found by difference, but if desired the solutions from the precipitation of the nitro-cellulose may be evaporated down upon the water bath at 30° to 40° C., and finally dried over CaCl_{2} until no smell of ether or chloroform can be detected, and the nitro- glycerine weighed. It will, however, always be much too low. An actual analysis of a sample of gelatine dynamite gave the following result:—
Nitrocellulose (collodion) 3.819 per cent.
Nitro-glycerine 66.691 "
Wood-pulp 16.290 "
KNO_{3} 12.890 "
Na_{2}CO_{3} Nil.
Water 0.340 "
This sample was probably intended to contain 30 per cent. of absorbing material to 70 per cent. of explosive substances. Many dynamites contain other substances than the above, such as paraffin, resin, sulphur, wood, coal-dust, charcoal, also mineral salts, such as carbonate of magnesia, chlorate of potash, &c. In these cases the above-described methods must of course be considerably modified. Paraffin, resin, and most of the sulphur will be found in the ether solution if present. The solution should be evaporated (and in this case the explosive should in the first case be treated with ether only, and not ether-alcohol), and the residue weighed, and then treated on the water bath with a solution of caustic soda. The resin goes into solution, and is separated by decantation from the residue, and precipitated by hydrochloric acid, and collected on a tarred filter (dried at 100° C.), and dried at 100° C. and weighed. The nitro- glycerine residue is treated with strong alcohol, decanted, and the residue of paraffin and sulphur washed with alcohol, dried, and weighed.
To separate the paraffin from the sulphur the residue is heated with a solution of ammonium sulphide. After cooling the paraffin collects as a crust upon the surface of the liquid, and by pricking a small hole through it with a glass rod the liquid underneath can be poured off, and the paraffin then washed with water, dried, and weighed. Sulphur is found by difference. Mr F.W. Smith (Jour. Amer. Chem. Soc., 1901, 23 [8], 585-589) determines the sulphur in dynamite gelatine as follows:—About 2 grms. are warmed in a 100 c.c. silver crucible on the water bath with an alcoholic solution of sodium hydroxide, and where the nitro-glycerine is decomposed, the liquid is evaporated to dryness. The residue is fused with 40 grms. of KOH and 5 grms. of potassium nitrate, the mass dissolved in dilute acetic acid and filtered, and the sulphates precipitated in the usual way. If camphor is present, it can be extracted with bisulphide of carbon after the material has been treated with ether-alcohol. In that case the sulphur, paraffin, and resin will also be dissolved. The camphor being easily volatile, can be separated by evaporation. Let the weight of the extract, freed from ether-alcohol before treatment with bisulphide of carbon, equal A, and the weight of extract after treatment with CS_{2} and evaporation of the same equal B; and weight of the residue which is left after evaporation of the CS_{2} and the camphor in solution equal C, the percentage of camphor will be A - B - C. The residue C may contain traces of nitro-glycerine, resin, or sulphur.
Camphor may be separated from nitro-glycerine by means of CS_{2}. If the solution of camphor in nitro-glycerine be shaken with CS_{2}, the camphor and a little of the nitro-glycerine will dissolve. The bisulphide solution is decanted, or poured into a separating funnel and separated from the nitro-glycerine. The two solutions are then heated on the water bath to 20° C. and then to 60° C., and afterwards in a vacuum over CaCl_{2} until the CS_{2} has evaporated from them. The camphor evaporates, and leaves the small quantity of nitro-glycerine which had been dissolved with it. The other portion is the nitro-glycerine, now free from CS_{2}. The two are weighed and their weights added together, and equals the nitro- glycerine present. There is a loss of nitro-glycerine, it being partly evaporated along with the CS_{2}. Captain Hess has shown that it is equal to about 1.25 per cent. This quantity should therefore be added to that found by analysis. Morton Liebschutz, in a paper in the Moniteur Scientifique for January 1893, very rightly observes that the variety of dynamites manufactured is very great, all of them having a special composition which, good or bad, is sometimes of so complicated a nature that the determination of their elements is difficult.
The determination of nitro-glycerine in simple dynamite No. 1 is easy; but not so when the dynamite contains substances soluble in ether, such as sulphur, resin, paraffin, and naphthalene. After detailing at length the methods he employs, he concludes with the observation that the knowledge of the use of acetic acid—in which nitro-glycerine dissolves—for the determination of nitro-glycerine may be serviceable. Mr F.W. Smith[A] gives the following indirect method of determining nitro-glycerine in gelatine dynamite, &c. About 15 grms. of the sample are extracted with chloroform in a Soxhlet apparatus, and the loss in weight determined. In a second portion the moisture is determined. A third portion of about 2 grms. is macerated with ether in a small beaker, the ethereal extract filtered, and the process of extraction repeated three or four times. The united filtrates are allowed to evaporate spontaneously, and the residue warmed gently on the water bath with 5 c.c. of ammonium sulphide solution, and 10 c.c. of alcohol until the nitro-glycerine is decomposed, after which about 250 c.c. of water and sufficient hydrochloric acid to render the liquid strongly acid, are added, and the liquid filtered. The precipitate is washed free from acid, and then washed through the filter with strong alcohol and chloroform into a weighed platinum dish, which is dried to constant weight at 50° C. The contents of the dish are now transferred to a silver crucible, and the sulphur determined. This amount of sulphur, deducted from the weight of the contents of the platinum dish, gives the quantity of substances soluble in chloroform with the exception of the nitro-glycerine, moisture, and sulphur. The amount of the former substances plus the moisture and sulphur, deducted from the total loss on extraction with chloroform, gives the quantity of nitro-glycerine. Nitro-benzene may be detected, according to J. Marpurgo, in the following manner:—In a porcelain basin are placed two drops of liquid phenol, three drops of water, and a fragment of potash as large as a pea. The mixture is boiled, and the aqueous solution to be tested then added. On prolonged boiling nitro-benzene produces at the edge of the liquid a crimson ring, which on the addition of a solution of bleaching powder turns emerald- green. And nitro-glycerine in ether solution, by placing a few drops of the suspected solution, together with a drop or two of aniline, upon a watch-glass, evaporating off the ether, and then adding a drop of concentrated sulphuric acid to the residue, when, if nitro-glycerine is present, the H_{2}SO_{4} will strike a crimson colour, due to the action of the aniline sulphate upon the nitric acid liberated from the nitro- glycerine.
[Footnote A: "Notes on the Analysis of Explosives," Jour. Amer. Chem.
Soc., 1901, 23 [8], 585-589.]
~Tonite.~—The analysis of this explosive is a comparatively easy matter, and can be performed as follows:—Weigh out 10 grms., or a smaller quantity, and boil with water in a beaker, decanting the liquid four or five times, and filter. The aqueous solution will contain the nitrate of barium. Then put the residue on the filter, and wash two or three times with boiling water. Evaporate the filtrate to dryness in a platinum dish. Dry and weigh. This equals the Ba(NO_{3})_{2}. If the sample is tonite No. 3, and contains di-nitro-benzol, treat first with ether to dissolve out this substance. Filter into a dish, and evaporate off the ether, and weigh the di-nitro-benzol, and afterwards treat residue with water as before. The residue is dried and weighed, and equals the gun-cotton present. It should then be treated with a solution of ether-alcohol in a conical flask, allowed to stand some three hours, then filtered through a weighed filter paper, dried at 40° C., and weighed. This will give the gun-cotton, and the difference between this last weight and the previous one will give the collodion-cotton. A portion of the residue containing both the gun- cotton and the soluble cotton can be tested in the nitrometer, and the nitrogen determined.
~Cordite.~—This explosive consists of gun-cotton (with a little collodion-cotton in it as impurity), nitro-glycerine, and vaseline—the proportions being given as 30 per cent. nitro-glycerine, 65 per cent. gun- cotton, and 5 per cent. vaseline. Its analysis is performed by a modification of the method given for gelatines. Five grms. may be dissolved in ether-alcohol in a conical flask, allowed to stand all night, and then filtered through a linen filter. The residue is washed with a little ether, pressed, and dried at 40° C., and weighed. It equals the gun-cotton. The solution contains the nitro-glycerine, soluble cotton, and vaseline. The cotton is precipitated with chloroform, filtered off, dried, and weighed. The two ether-alcohol solutions are mixed, and carefully evaporated down in a platinum dish upon the water bath at a low temperature. The residue is afterwards treated with strong 80 per cent. acetic acid, which dissolves out any nitro-glycerine left in it. The nitro-glycerine is then obtained by difference, or the method suggested to me privately by Mr W.J. Williams may be used. The residue obtained by evaporation of the ether-alcohol solution, after weighing, is treated with alcoholic potash to decompose the nitro-glycerine, water is added and the alcohol evaporated off. Some ether is then added, and the mixture shaken, and the ether separated and evaporated, and the residue weighed as vaseline.
The moisture should, however, be determined by the method devised by Mr Arthur Marshall, F.I.C., of the Royal Gunpowder Works, Waltham Abbey, which is carried out as follows:—The cordite or other explosive is prepared in the manner laid down for the Abel heat test, that is t say, it is ground in a small mill, and that portion is selected which passes through a sieve having holes of the size of No. 8 wire gauge, but not through one with holes No. 14 wire gauge.