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. of nitric acid,
and 10 cwt. of sulphuric acid, and 247 lbs. of glycerine.

Upon reference to the equation showing the formation of nitro-glycerine,
it will be seen that for every 1 lb. of glycerine 2.47 lbs. of nitro-
glycerine should be furnished,[A] but in practice the yield is only a
little over 2 lbs., the loss being accounted for by the unavoidable
formation of some of the lower nitrate of glycerine (the mono-nitrate),
which afterward dissolves in the washing waters. The lead tank (Fig. 5) is
generally cased in woodwork, with a platform in front for the man in
charge of the nitrating to stand upon, and whence to work the various
taps. The top of the tank is closed in with a dome of lead, in which is a
small glass window, through which the progress of the nitrating operation
can be watched. From the top of this dome is a tube of lead which is