The guhr is generally dried in a reverberatory muffle furnace. It is
spread out on the bottom to the thickness of 3 or 4 inches, and should
every now and then be turned over and raked about with an iron rabble or
hoe. The temperature should be sufficiently high to make the guhr red hot,
or the organic matter will not be burnt off. The time occupied in
calcining will depend of course upon the quality of the guhr being
operated upon. Those containing a high percentage of water and organic
matter will of course take longer than those that do not. A sample of the
calcined guhr should not contain more than 0.5 per cent. of moisture and
organic matter together.

After the guhr is dry it requires to be sifted and crushed. The crushing
is done by passing it between iron rollers fixed at the bottom of a cone
or hopper, and revolving at a moderate speed. Beneath the rollers a fine
sieve should be placed, through which the guhr must be made to pass.

The kieselguhr having been dried, crushed, and sifted, should be packed
away in bags, and care should be taken that it does not again absorb
moisture, as if it contains anything above about five-tenths per cent. of
water it will cause the dynamite made with it to exude. The guhr thus
prepared is taken up to the danger area, and mixed with nitro-glycerine.
The nitro-glycerine used should be quite free from water, and clear, and
should have been standing for a day or two in the precipitating house. The
guhr and nitro-glycerine are mixed in lead tanks (about 1-1/2 foot deep,
and 2 to 3 feet long), in the proportions of 75 of the nitro-glycerine to
25 of the guhr, unless the guhr is found to be too absorbent, which will
cause the dynamite to be too dry and to crumble. In this case a small
quantity of barium sulphate, say about 1 per cent., should be added to the
guhr. This will lessen its absorbing powers, or a highly absorptive sample