occasionally turned over by hand in order that a fresh surface may be
continually exposed to the action of the hot air. The building itself may
be heated by means of hot-water pipes, but on no account should any of the
pipes be exposed. They should all be most carefully covered over with
wood-work, because when the dry nitro-cotton is moved, as in turning it
over, very fine particles get into the air, and gradually settling on the
pipes, window ledges, &c., may become very hot, when the slightest
friction might cause explosion. It is on this account that this house
should be very carefully swept out every day. It is also very desirable
that the floor of this house should be covered with oilcloth or linoleum,
as being soft, it lessens the friction.

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° 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