ery apt to
become hot, and decomposition, which sets up in spots where a little
globule of nitro-glycerine is floating, surrounded by acids that gradually
get hot, gives off nitrous fumes, and perhaps explodes, and thus causes
the sudden explosion of the whole. The only way to prevent this is for the
workman in charge to look at the thermometers _frequently_, and at the
colour of the escaping fumes, and if he should notice a rise of
temperature or any appearance of red fumes, to turn on the water and air,
and stir up the mixture, when probably the temperature will suddenly fall,
and the fumes cease to come off.

The cause of explosions in this building is either the non-attention of
the workmen in charge, or the bursting of one of the water pipes, by which
means, of course, the water, finding its way into the acids, causes a
sudden rise of temperature. If the latter of these two causes should
occur, the water should at once be shut off and the air turned on full,
but if it is seen that an explosion is likely to occur, the tank should at
once be emptied by allowing its contents to run away into a drowning tank
placed close outside the house, which should be about 4 feet deep, and
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