tment.

The length of the boil depends upon the kiers; with the open kier about
ten hours are usually given, with the Barlow and injector kiers, working
at a pressure of 40 lb. to 50 lb., six to seven hours are given.

(5) =Lime or Grey Sour.=--After the lime boil, the next operation is
that of the lime sour or grey sour as it is often called to distinguish
it from a subsequent souring. The souring is done in a machine
constructed in the same way as a washing machine; the trough of the
machine is filled with hydrochloric acid at 2 deg. Tw., which is kept ready
prepared in a stone cistern and run into the machine as required (it is
not advisable to use acid stronger than this). After passing through the
sour the goods are piled in a heap on the stillage for a few hours. The
acid attacks the lime soap which was formed during the lime boil,
decomposes it and dissolves out the lime with the formation of calcium
chloride, while the fat of the soap is liberated, the former is washed
away in the subsequent washing, while the latter remains to a large
extent on the goods, and is removed by the lye boil that follows.
Sulphuric acid is not so satisfactory to use for the lime sour as
hydrochloric acid, because it forms with the lime the insoluble sulphate
of calcium, which is difficult to entirely remove from the goods,
whereas the chloride is very soluble and is entirely eliminated from the
goods by the washing that follows.

It is advisable to keep the acid at a uniform strength in the machine.
The Twaddell is here of no use as an indicator of the actual strength,
because the lime which the acid dissolves, while it neutralises and
reduces the strength of the acid, actually raises the Twaddell, under
which circumstance the only safe method is a chemical test. This can be
carried out very simply and with a sufficient degree of accuracy by the
workmen, and if it be done at regular intervals during the souring, and
the supply of the fresh acid be regulated, the sour will be kept at a
more uniform strength and more uniform results will be obtained than if
the souring were done in a more empirical fashion. The test is best and
most easily done as follows:--

Prepare a solution of 1 oz. of the powdered high strength 98 per cent.
caustic soda in 1 pint of water, weighing and measuring these quantities
very carefully. Now take a tall, narrow, white bottle of about 5 oz.
capacity and make a mark on the neck. Fill this bottle with the t