en run in by introducing _n_ and opening the valve at its bottom, the
contents of the vessel being agitated by air blown through the
perforations of the pipe _g_. When the glycerine is all nitrated and the
temperature has slightly fallen, the circulation of the water through the
coils _h_ and the air-stirring are stopped, and the glycerine supply
vessel _n_ is removed. The nitro-glycerine as it separates from the acids
is raised by introducing by the pipe _f_ waste acid from a previous
charge, this displacing the nitro-glycerine upwards and causing it to flow
by the outlet, _j_ and pipe _k_ to the prewash tank. When nearly all the
nitro-glycerine has been separated in this manner the acids in the
apparatus may be run off by the pipe _b_ to an after separating vessel for
further settling, thus leaving the apparatus free for another nitration,
or the nitrating vessel itself may be used as an after separating bottle
displacing the nitro-glycerine with waste acid as it rises to the top, or
skimming off in the usual manner. When the separation of the nitro-
glycerine is complete the waste acid is run off and denitrated as usual, a
portion of it being reserved for the displacement of the nitro-glycerine
in a subsequent operation.

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 deg. 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