be more or less unsuitable for the manufacture
of nitro-glycerine, where a number of buildings are required to be upon
different levels, in order to allow of the flow of the liquid nitro-
glycerine from one building to another through a system of conduits. These
conduits (Fig. 1), which are generally made of wood and lined with lead,
the space between the woodwork and the lead lining, which is generally
some 4 or 5 inches, being filled with cinders, connect the various
buildings, and should slope gently from one to the other. It is also
desirable that, as far as possible, they should be protected by earth-work
banks, in the same way as the danger buildings themselves. They should
also be provided with covers, which should be whitewashed in hot weather.

A great deal of attention should be given to these conduits, and they
should be very frequently inspected. Whenever it is found that a portion
of the lead lining requires repairing, before cutting away the lead it
should be very carefully washed, for several feet on either side of the
portion that it is intended to remove, with a solution of caustic soda or
potash dissolved in methylated spirit and water, and afterwards with water
alone. This decomposes the nitro-glycerine forming glycerine and potassium
nitrate. It will be found that the mixed acids attack the lead rather
quickly, forming sulphate and nitrate of lead, but chiefly the former. It
is on this account that it has been proposed to use pipes made of
guttapercha, but the great drawback to their use is that in the case of
anything occurring inside the pipes, such as the freezing of the nitro-
glycerine in winter, it is more difficult to find it out, and the
condition of the inside cannot be seen, whereas in the case of wooden
conduits it is an easy matter to lift the lids along the whole length of
the conduit.

The buildings which require to be connected by conduits are of course
those concerned with the manufacture of nitro-glycerine. These buildings
are--(1) The nitrating house; (2) the separating house; (3) the filter
house; (4) the secondary separator; (5) the deposit of washings; (6) the
settling or precipitation house; and each of these buildings must be on a
level lower than the preceding one, in order that the nitro-glycerine or
acids may flow easily from one building to the next. These buildings are,
as far as possible, best placed together, and away from the other danger
buildings, such as the cartridg