hem 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.

The mixed acids having been forced up to the danger area, and to a level
higher than the position of the nitrating house, should, before being
used, be allowed to cool, and leaden tanks of sufficient capacity to hold
at least enough acid for four or five nitrations should be placed in a
wooden house upon a level at least 6 or 7 feet above the nitrating house.
In this house also should be a smaller lead tank, holding, when filled to
a certain mark, just enough of the mixed acids for one nitration. The
object of this tank is, that as soon as the man in charge knows that the
last nitration is finished, he refills this smaller tank (which contains
just enough of the mixed acids), and allows its contents to flow down into
the nitrating house and into the nitrator, ready for the next nitration.
The nitration is usually conducted in a vessel constructed of lead, some 4
feet wide at the bottom, and rather less at the top, and about 4 feet or
so high. The size, of course, depends upon the volume of the charge it is
intended to nitrate at one operation, but it is always better that the
tank should be only two-thirds full. A good charge is 16 cwt. of the mixed
acids, in the proportion of three to five; that is, 6 cwt. o