Blasting Gelatine and Gelatine Dynamite.—­The gelatine explosives chiefly in use are known under the names of blasting gelatine, gelatine dynamite, and gelignite.  They all consist of the variety of nitro-cellulose known as collodion-cotton, i.e., a mixture of the penta- and tetra-nitrates dissolved in nitro-glycerine, and made up with various proportions of wood-pulp, and some nitrate, or other material of a similar nature.  As the gun-cotton contains too little oxygen for complete combustion, and the nitro-glycerine an excess, a mixture of the two substances is very beneficial.

Blasting gelatine consists of collodion-cotton and nitro-glycerine without any other substance, and was patented by Mr Alfred Nobel in 1875.  It is a clear, semi-transparent, jelly-like substance, of a specific gravity of 1.5 to 1.55, slightly elastic, resembling indiarubber, and generally consists of 92 per cent. to 93 per cent. of nitro-glycerine, and 7 to 8 per cent. of nitro-cotton.  The cotton from which it is made should be of good quality.  The following is the analysis of a sample of nitro-cellulose which made very good gelatine:-

Soluble cotton 99.118 per cent. 
Gun-cotton 0.642 "
Non-nitrated cotton 0.240 "
Nitrogen 11.64 "
Total ash 0.25 "

The soluble cotton, which is a mixture of the tetra- and penta-nitrates, is soluble in ether-alcohol, and also in nitro-glycerine, and many other solvents, whereas the hexa-nitrate (gun-cotton), C_{12}H_{14}O_{4}(ONO_{2})_{6}, is not soluble in the above liquids, although it is soluble in acetone or acetic ether.  It is very essential, therefore, that the nitro-cotton used in the manufacture of the gelatine explosives should be as free as possible from gun-cotton, otherwise little lumps of undissolved nitro-cotton will be left in the finished gelatine.  The non-nitrated or unconverted cotton should also be very low, in fact considerably under 1/2 per cent.

The nitro-cotton and the nitro-glycerine used should always be tested before use by the heat test, because if they do not separately stand this test, it cannot be expected that the gelatine made from them will do so.  It often occurs, however, that although both the ingredients stand this test separately before being mixed, that after the process of manufacture one or other or both fail to do so.

The nitro-cotton most suitable for gelatine making is that which has been finely pulped.  If it is not already fine enough, it must be passed through a fine brass wire sieve.  It will be found that it requires to be rubbed through by hand, and will not go through at all if in the least degree damp.  It is better, therefore, to dry it first.  The percentage of nitrogen in the nitrated cotton should be over 11 per cent.  It should be as free as possible from sand or grit, and should give but little ash upon ignition, not more than 0.25 per cent.