List shoes should always be worn in this building, and a thermometer hung up somewhere about the centre of the house, and one should also be kept in one of the trays to give the temperature of the cotton, especially the bottom of the trays.  The one nearest to the hot air inlet should be selected.  If the temperature of the house is kept at about 40 deg.  C. it will be quite high enough.  The building must of course be properly ventilated, and it will be found very useful to have the walls made double, and the intervening space filled with cinders, and the roof covered with felt, as this helps to prevent the loss of heat through radiation, and to preserve a uniform temperature, which is very desirable.

The dry cotton thus obtained, if not already fine enough, should be sifted through a brass sieve, and packed away ready for use in zinc air-tight cases, or in indiarubber bags.  The various gelatine compounds, gelignite, gelatine dynamite, and blasting gelatine, are manufactured in exactly the same way.  The forms known as gelatine dynamite differ from blasting gelatine in containing certain proportions of wood-pulp and potassium nitrate, &c.  The following are analyses of some typical samples of the three compounds:—­

Gelatine       Blasting
Gelignite.   Dynamite.       Gelatine.

Nitro-glycerine 60.514 71.128 92.94 per cent. 
Nitro-cellulose 4.888 7.632 7.06 "
Wood-pulp 7.178 4.259 ... "
Potassium nitrate 27.420 16.720 ... "
Water ... 0.261 ... "

The gelignite and gelatine dynamites consist, therefore, of blasting gelatine, thickened up with a mixture of absorbing materials.  Although the blasting gelatine is weight for weight more powerful, it is more difficult to make than either of the other two compounds, it being somewhat difficult to make it stand the exudation and melting tests.  The higher percentage of nitro-cotton, too, makes it expensive.

When the dry nitro-cotton, which has been carefully weighed out in the proportions necessary either for blasting gelatine or any of the other gelatine explosives, is brought to the gelatine making house, it is placed in a lead-lined trough, and the necessary quantity of pure dry nitro-glycerine poured upon it.  The whole is then well stirred up, and kept at a temperature of from 40 deg. to 45 deg.  C. It should not be allowed to go much above 40 deg.  C.; but higher temperatures may be used if the nitro-cotton is very obstinate,[A] and will not dissolve.  Great caution must, however, be observed in this case.  The mixture should be constantly worked about by the workman with a wooden paddle for at least half an hour.  At a temperature of 40 deg. to 45 deg. the nitro-glycerine acts upon the nitro-cotton and forms a jelly.  Without heat the gelatinisation is very imperfect indeed, and at temperatures under 40 deg.  C. takes place very slowly.