rs they
form are not always fast to washing and soaping. It has been
ascertained, however, that some of the direct dyes, _e.g._, Benzo
azurine, Chicago blue, Catechu browns, Diamine blues, Diamine browns,
etc., are capable of uniting with metallic bodies to form insoluble
colour lakes, and this combination can take place on the fibre. Fast
shades may be dyed with the dye-stuffs named above, and with others of
this group, by first dyeing them in the usual way, then passing through
a boiling bath containing bichromate of potash or copper sulphate,
either together or separately. The two fixing agents here named have
been found to be the best, although others, as, for instance, zinc
sulphate, chromium fluoride and iron sulphate have been tried. With some
dyes there is little or no alteration in shade, but in others there is
some change, thus the blues as a rule tend to become greener in tone,
and browns also tend to acquire a greener tone and deeper shade. The
treated shades thus obtained are notable for considerable fastness to
washing, soaping and light. It is to be noted that bichromate of potash
exercises both a fixing and an oxidising action on dye-stuffs, hence it
is needful to use it with some degree of caution and not in too great an
amount, otherwise with some dyes there is a risk of over-oxidation, and
in consequence poor shades will be developed. The following recipes will
serve to show what dyes may thus be used, and the colours that can be
obtained with them.

_Dark Red._--Use in the dye-bath 3 lb. Diamine fast red F, 3 lb. soda
and 20 lb. Glauber's salt, work at the boil for one hour, then lift,
rinse and pass into a boiling bath containing 3 lb. fluoride of chromium
for ten to fifteen minutes, then lift, rinse and dry. By using 1 lb. of
the dye-stuff in the same way a light red shade is got.

_Orange._--Dye at the boil for one hour with 1 lb. Chrysamine G, 3 lb.
soap and 10 lb. Glauber's salt, then rinse and fix in a fresh boiling
bath with 1 lb. bichromate of potash, 3 lb. sulphate of copper and 2 lb.
acetic acid.

_Yellow._--Dye with 3-1/2 lb. Diamine yellow N, 3 lb. soap and 15 lb.
phosphate of soda, then fix with 4 lb. fluoride of chromium.

_Gold Yellow._--Prepare the dye-bath with 3 lb. Benzo chrome brown 5 G,
1 lb. soda ash, 12 lb. Glauber's salt. Dye at the boil for one hour and
rinse. This gives an orange brown. To get the yellow shade, afterwards
chrome with 3 lb. bichromate of potash, 3 lb. sul