fter working
them for a day to replenish them with a little indigo, soda, or
potash, as the case may be, and a little bran.

Cleaner vats are obtained if treacle be substituted for the bran, but
the latter ferments better, and gives better results in working.

#Urine-Indigo Vat.#--This vat has almost, if not quite, gone out of use,
being a rather unpleasant vat to work with, with few advantages over
other vats. One advantage it possesses over the woad and potash vats
is that it is the best for working on a small scale, but the modern
zinc reduction vats run it very close in this respect. The vat is (p. 146)
made as follows: To 50 gallons of stale urine 4 lb. of common salt are
added, and the mixture heated to from 120 deg. F. to 140 deg. F. Then
1 lb. madder and 1 lb. ground indigo are added, and the mass is well
stirred. Then the mixture is allowed to stand until the indigo is
completely reduced, when the vat is ready for dyeing.

#Indigo-Indophenol Vat.#--Messrs. Durand, Huguenin & Co. have introduced
the use of Indophenol along with indigo in wool dyeing. Indophenol can
be reduced in the same way as indigo, and fibres dipped in this
reduced product on exposure to air turn blue in the same way as if
dipped in an indigo vat.

By itself indophenol has not met with much favour from dyers for a
variety of reasons, but it has been found that, mixed with indigo, it
can be used in dyeing with some advantage on the score of cheapness.
The newly mixed vat is made in the following manner:--

In a convenient vessel 26 gallons of water, 15 lb. zinc dust, ground
into a paste with 6 gallons of water, and 7 gallons bisulphite of soda
of 55 deg. Tw. strong are mixed. Then 8 pints caustic soda lye of 72 deg.
Tw., and 16 pints liquor ammonia are added, and the whole mass is well
stirred up; 22 lb. good indigo of about 70 per cent. indigotine and
7-1/4 lb. Indophenol are thoroughly ground into a paste with 7 gallons
of water and 2 pints caustic soda lye of 72 deg. Tw. The paste is added
to the previous mixture, and, after being well stirred in, sufficient
water is added to make the total volume of liquor up to 100 gallons.
The mass is stirred up from time to time during a period of from
thirty-six to forty-eight hours, by which time, as a rule, the indigo
and Indophenol will have been completely reduced, and the vat have
acquired a canary-yellow colour; if it has not, add a little more zinc
dust and bisulphite of soda. It is ready