through which the compressed air was made to pass; but the process was not
found to be of a very satisfactory nature, and it is certainly better not
to allow the formation of these compounds in the manufacture of the acid
in the first instance. Another plan, however, is to heat the acid gently,
and thus drive out the nitrous gases. Both processes involve loss of
nitric acid.

Having obtained nitric and sulphuric acids as pure as possible, the next
operation is to mix them. This is best done by weighing the carboys in
which the acids are generally stored before the acids are drawn off into
them from the condensers, and keeping their weights constantly attached to
them by means of a label. It is then a simple matter to weigh off as many
carboys of acid as may be required for any number of mixings, and subtract
the weights of the carboys. The two acids should, after being weighed, be
poured into a tank and mixed, and subsequently allowed to flow into an
acid egg or montjus, to be afterwards forced up to the nitrating house in
the danger area. The montjus or acid egg is a strong cast-iron tank, of
either an egg shape, or a cylinder with a round end. If of the former
shape, it would lie on its side, and upon the surface of the ground, and
would have a manhole at one end, upon which a lid would be strongly bolted
down; but if of the latter shape, the lid, of course, is upon the top, and
the montjus itself is let into the ground. In either case, the principle
is the same. One pipe, made of stout lead, goes to the bottom, and another
just inside to convey the compressed air, the acids flowing away as the
pressure is put on, just as blowing down one tube of an ordinary wash-
bottle forces the water up the other tube to the jet. The pressure
necessarily will, of course, vary immensely, and will depend upon the
height to which the acid has to be raised and the distance to be
traversed.