I have found, however, that much quicker, and quite as accurate, results may be obtained by leaving the dynamite in contact with ether in a small Erlenmeyer flask for twenty-four hours—­leaving it overnight is better—­ and decanting, and again allowing the substance to remain in contact with a little fresh ether for an hour, and finally filtering through a weighed filter, drying at 100 deg.  C., and weighing.  This gives the weight of the kieselguhr.  The nitro-glycerine must be obtained by difference, as it is quite useless to evaporate down the ethereal solution to obtain it, as it is itself volatile to a very considerable extent at the temperature of evaporation of the ether, and the result, therefore, will always be much too low.  The dry guhr can, of course, be examined, either qualitatively or quantitatively, for other mineral salts, such as carbonate of soda, &c.  An actual analysis of dynamite No. 1 made by the author at Hayle gave—­ Moisture, 0.92 per cent.; kieselguhr, 26.15 per cent.; and nitro-glycerine, 72.93 per cent., the last being obtained by difference.

Nitro-Glycerine.—­It is sometimes desired to test an explosive substance for nitro-glycerine.  If an oily liquid is oozing from the substance, soak a drop of it in filter paper.  If it is nitro-glycerine it will make a greasy spot.  If the paper is now placed upon an iron anvil, and struck with an iron hammer, it will explode with a sharp report, if lighted it burns with a yellowish to greenish flame, emitting a crackling sound, and placed upon an iron plate and heated from beneath, it explodes sharply.

If a few drops of nitro-glycerine are placed in a test tube, and shaken up with methyl-alcohol (previously tested with distilled water, to see that it produces no turbidity), and filtered, on the addition of distilled water, the solution will become milky, and the nitro-glycerine will separate out, and finally collect at the bottom of the tube.

If to a solution of a trace of nitro-glycerine in methyl-alcohol, a few drops of a solution, composed of 1 volume of aniline, and 40 volumes sulphuric acid (1.84) be added, a deep purple colour will be produced.  This colour changes to green upon the addition of water.  If it is necessary to determine the nitro-glycerine quantitatively in an explosive, the scheme on page 213 may be followed.  Ether is the best solvent to use.  Nitrogen should be determined in the nitrometer.

Gelatine Compounds.—­The simplest of these compounds is, of course, blasting gelatine, as it consists of nothing but nitro-cotton and nitro-glycerine, the nitro-cellulose being dissolved in the glycerine to form a clear jelly, the usual proportions being about 92 per cent. of nitro-glycerine to 8 per cent. nitro-cotton, but the cotton is found as high as 10 per cent. in some gelatines.  Gelatine dynamite and gelignite are blasting gelatines, with varying proportions of wood-pulp and saltpetre (KNO_{3}) mixed