In a further patent (Eng. Pat. 3,020, 1903) the authors propose with the
object of preventing the formation and separation of nitro-glycerine in
the waste acids, after the nitro-glycerine initially formed in the
nitrating vessel has been separated and removed, to add a small quantity
of water to the waste acids; this is carried out as follows. A relatively
small quantity of water is added, and this prevents all further separation
of nitro-glycerine, and at the same time the strength of the waste acids
is so slightly reduced that their separation and re-concentration are not
affected. "After-separation" is thus done away with, and the nitro-
glycerine plant simplified and its output increased. After nitration
separation is commenced at a temperature such that when all the displacing
acid has been added, and the separation of the nitro-glycerine is
complete, the temperature of the contents of the nitrating vessel shall
not be lower than 15° C. A sufficient quantity of the displacing acid is
then run off through the waste-acid cock to allow of the remaining acids
being air-stirred without splashing over the top. A small quantity of
water, from 2 to 3 per cent. according to strength of acid; if waste
consists of sulphuric acid (monohydrate), 62 per cent.; nitric acid
(anhydrous), 33 per cent. and water 5 per cent.; temperature 15° C., then
2 per cent. of water is added; if waste acids contain less than 4 per
cent. of water of temperature lower than 15° C., from 3 to 5 per cent. of
water may have to be added. The water is added slowly through the
separator cylinder, and the contents of the nitrator air-stirred, but not
cooled, the temperature being allowed to rise slowly and regularly as the
water is added--usually about 3° C. for each per cent. of water added.
When air-agitation has been stopped, the acids are kept at rest for a
short time, in order to allow of any small quantity of initially formed
nitro-glycerine adhering to the coils and sides of the vessel rising to
the top. When this has been separated by displacement, the acids are ready
for denitration, or can be safely stored without further precaution.