arrival of the nitro-glycerine at this house,
it first flows into a lead-lined wooden tank (W), containing a compressed
air pipe, just like the one in the small tank in the separating house.
This tank is half filled with water, and the compressed air is turned on
from half to a quarter of an hour after the introduction of the charge.
The water is then drawn off, and fresh water added. Four or five washings
are generally necessary. The nitro-glycerine is then run into the next
tank (A), the top of which is on a level with the bottom of the first one.
Across the top of this tank is stretched a frame of flannel, through which
the nitroglycerine has to filter. This removes any solid matters, such as
dirt or scum. Upon leaving this tank, it passes through a similar flannel
frame across another tank (B), and is finally drawn off by a tap in the
bottom of the tank into rubber buckets. The taps in these tanks are best
made of vulcanite.

At this stage, a sample should be taken to the laboratory and tested. If
the sample will not pass the tests, which is often the case, the charge
must be rewashed for one hour, or some other time, according to the
judgment of the chemist in charge. In the case of an obstinate charge, it
is of much more avail to wash a large number of times with small
quantities of water, and for a short time, than to use a lot of water and
wash for half an hour. Plenty of compressed air should be used, as the
compound nitric ethers which are formed are thus got rid of. As five or
six charges are often in this house at one time, it is necessary to have
as many tanks arranged in tiers, otherwise one or two refractory charges
would stop the nitrating house and the rest of the nitro-glycerine plant.
The chief causes of the washed material not passing the heat test are,
either that the acids were not clean, or they contained objectionable
impurities, or more frequently, the quality of the glycerine used. The
glycerine used for making nitro-glycerine should conform to the following
tests, some of which, however, are of greater importance than others. The
glycerine should--

1. Have minimum specific gravity at 15 deg. C. of 1.261.

2. Should nitrify well.

3. Separation should be sharp within half an hour, without the separation
of flocculent matter, nor should any white flocculent matter (due to fatty
acids) be formed when the nitrated glycerine is thrown into water and
neutralised with carbonate of soda.

4. Sho