in an inert substance, forming a plastic mass. In his patent he says:
"This invention relates to the use of nitro-glycerine in an altered
condition, which renders it far more practical and safe for use. The
altered condition of the nitro-glycerine is effected by causing it to be
absorbed in porous unexplosive substances, such as charcoal, silica,
paper, or similar materials, whereby it is converted into a powder, which
I call dynamite, or Nobel's safety powder. By the absorption of the nitro-
glycerine in some porous substance it acquires the property of being in a
high degree insensible to shocks, and it can also be burned over a fire
without exploding."

Ordinary dynamite consists of a mixture of 75 per cent. of nitro-glycerine
and 25 per cent. of kieselguhr. The guhr as imported (Messrs A. Haake &
Co. are the chief importers) contains from 20 to 30 per cent. of water and
organic matter. The water may be very easily estimated by drying a weighed
quantity in a platinum crucible at 100° C. for some time and re-weighing,
and the organic matter by igniting the residue strongly over a Bunsen
burner. Before the guhr can be used for making dynamite it must be
calcined, in order not only to get rid of moisture, but also the organic
matter.

A good guhr should absorb four times its weight of nitro-glycerine, and
should then form a comparatively dry mixture. It should be pale pink, red
brown, or white. The pink is generally preferred, and it should be as free
as possible from grit of all kinds, quartz particles, &c., and should have
a smooth feeling when rubbed between the finger and thumb, and should show
a large quantity of diatoms when viewed under the microscope. The
following was the analysis of a dried sample of kieselguhr:--Silica,
94.30; magnesia, 2.10; oxide of iron and alumina, 1.3; organic matter,
0.40; moisture, 1.90 per cent.