nitroglycerine upon the paper.

The exudation test consists in freezing and thawing the gelatine three
times in succession. Under these conditions there should be no exudation
of nitro-glycerine. All the materials used in the manufacture of gelatine
explosives should be subjected to analytical examination before use, as
success largely depends upon the purity of the raw materials. The
wood-pulp, for instance, must be examined for acidity.

~Properties of the Gelatine Compounds.~--Blasting gelatine is generally
composed of 93 to 95 parts nitro-glycerine, and 5 to 7 parts of nitro-
cellulose, but the relative proportions of explosive base and nitro-
glycerine, &c., in the various forms of the gelatine explosives do not
always correspond to those necessary for total combustion, either because
an incomplete combustion gives rise to a greater volume of gas, or because
the rapidity of decomposition and the law of expansion varies according to
the relative proportions and the conditions of application. The various
additions to blasting gelatine generally have the effect of lowering the
strength by reducing the amount of nitro-glycerine, but this is sometimes
done in order to change a shattering agent into a propulsive force. If
this process be carried too far, we of course lose the advantages due to
the presence of nitro-glycerine. There is therefore a limit to these
additions.[A]

[Footnote A: Mica is said to increase the rapidity of explosion when mixed
with gelatine.]

The homogeneousness and stability of the mixture are of the highest
importance. It is highly essential that the nitro-glycerine should be
completely absorbed by the substances with which it is mixed, and that it