ed and dried cotton is worked three-quarters of an hour in a vat
containing a tannin solution (1 oz. per gallon). The cotton remains in
this liquid, which is allowed to cool off for twelve hours, then it is
hydro-extracted. Sumac turns the shade somewhat greener, which is
noticed especially after bleaching, therefore tannin is given the
preference.

_Chromium Mordant._

The cotton treated with tannin and then hydro-extracted is worked cold
for one hour in a vat containing a solution of chromium chloride at 32 deg.
Tw., and remains in this solution twelve hours. The cotton is then
hydro-extracted and washed directly; it is best to employ running water.
A special fixation does not take place. The cotton is now ready for
dyeing. The solution of chromium chloride and the tannin solution can be
used continuously, adding fresh liquor to keep the baths up to strength.

_Dyeing_--For dyeing, water free from lime must be used. Water having
not more than 2.5 deg. hardness can be employed if it is corrected with
acetic acid, thereby converting the carbonate of lime into acetate of
lime. Very calcareous water must be freed from lime before use. The
dye-bath contains for 100 lb. cotton 15 lb. Alizarine blue paste (A R or
F, according to the shade desired), 35 lb. acetic acid (12 deg. Tw.), 15-1/2
lb. ammonia (25 per cent.), 2-1/4 oz. tannin. The cotton is worked a
quarter of an hour in the cold; the temperature is raised slowly to a
boil, taking about one hour, and the cotton is worked three-quarters of
an hour at that heat. Finally the cotton is washed and hydro-extracted.
The dyed and washed cotton is steamed two hours at 15 lb. to 22 lb.
pressure. Steaming turns the shade greener and darker, and increases the
fastness. After steaming the cotton it is soaped one or two hours at the
boil, with or without pressure. According to the quality of water
employed, 2 to 5 parts soap per 1,000 parts water are taken.

_Brown._--A fine brown is got by a similar process to this, if instead
of Alizarine blue, Alizarine orange is used in the dye-bath. A deeper
brown still if Anthracene brown, or a mixture of Anthracene brown and
Alizarine blue, be used.

_Claret Red._--Clarets to maroon shade of red are got by preparing the
cotton as for blue given above, then dyeing with alizarine.

_Logwood Black._--One of the most important colours that come under this
section is logwood black, the formation of which on the fibre depends
upon the fact t