some 16 feet long by 6 feet wide; in fact, large enough to hold a
considerable quantity of water. But this last course should only be
resorted to as a last extremity, as it is extremely troublesome to recover
the small quantity of nitro-glycerine from the bottom of this tank, which
is generally a bricked and cemented excavation some few yards from the
house.

It has been proposed to treat these waste acids, containing nitro-
glycerine, in Mr M. Prentice's nitric acid retort. In this case they would
be run into the retort, together with nitrate of soda, in a fine stream,
and the small quantity of nitro-glycerine, coming into contact with the
hot mixture already in the retort, would probably be at once decomposed.
This process, although not yet tried, promises to be a success. Several
processes have been used for the denitration of these acids.

~Treatment of the Waste Acid from the Manufacture of Nitro-Glycerine and
Gun-Cotton.~--The composition of these acids is as follows:--

Nitro-glycerine and Gun-cotton
Waste Acid.

Sulphuric acid 70 per cent. 78 per cent.
Nitric acid 10 " 12 "
Water 20 " 10 "

The waste acid from the manufacture of gun-cotton is generally used direct
for the manufacture of nitric acid, as it contains a fairly large amount
of sulphuric acid, and the small amount of nitro-cellulose which it also
generally contains decomposes gradually and without explosion in the
retort. Nitric acid may be first distilled off, the resulting sulphuric