44 
POPULAR SCIENCE REVIEW. 
tliis means the materials are obtained of a uniform quality and 
perfectly pure. The saltpetre comes from various districts of 
India, chiefly from Bengal and Oude, where it is found mixed 
with the soil, and as an incrustation on the ground. In India 
it is boiled, and roughly crystallised by evaporation. When it 
is required for use in the (tunpowder Factory, it is purified by 
a process founded on the principle that hot water will receive in 
solution more of the saltpetre than of the impurities mingled 
with it. The saltpetre is boiled in water ; the resulting solution 
is then filtered and allowed to cool in large vats, at the bottom 
of which the pure saltpetre is deposited in fine crystals. It is 
then washed, dried, and stored in bins, great care being taken 
that no sand or gritty particles are introduced, as they might 
cause an explosion when under pressure at subsequent stages of 
the manufacture, and the same precaution is taken with the 
sulphur and the charcoal. It is believed that many of the ex- 
plosions which occur in private factories are caused by foreign 
substances being present in the materials. 
The sulphur is all of the best quality, imported from Sicily. 
It is purified by a distilling process, which reduces it from its 
rough state to masses of handsome yellow crystals. It is then 
pulverised by being ground under iron runners, and sifted in a 
kind of revolving cylindrical sieve, called a “ slope reel.” The 
sulphur refining-liouse is, of the whole factory, the least pleasant 
portion for a visitor, the air being always tainted with the 
fumes of the sulphur, which are so strong as even to burn and 
destroy the leaves of the trees near the building. The manage- 
ment of the process is, however, by no means an unhealthy 
labour. The workman last employed at it died as a pensioner 
at the ripe old age of eighty, after having worked forty years in 
the refining-house. 
The charcoal is all made on the spot, chiefly from wood im- 
ported from Holland and Grermany. The alders and willows in 
the plantations of the factory furnish but an insignificant supply, 
probably not enough to make a dozen barrels in the year. They 
are grown for the most part to form screens around and between 
the houses, so as to diminish the danger resulting from a pos- 
sible explosion. The wood employed is of three kinds — alder 
and willow, which are used for common powder, and black dog- 
wood for fine rifle powder for the Snider and Martini-Henry. 
The latter wood is really a kind of buckthorn (. Rhamnus fran- 
gula ), of slow growth, and, consequently, close grain, which 
forms dense thickets in the forests of Grermany, and is also 
found in the north of England and elsewhere. It is imported 
in bundles of slender rods about six feet long, and enormous 
quantities of these bundles may be seen stacked in the fields of 
the factory. There it is kept for at least three years, though 
