simply weighed out and added slowly to the
water. If added too quickly the hydrosulphite will cake, fall to the
bottom and be difficult to dissolve.

To the saucepan containing the indigo (100 per cent) add 7 fluid ozs.
of the caustic soda solution, then gradually add 3-1/2 pints of
hydrosulphite solution, stirring gently for 15 to 20 minutes. Heat
the saucepan to 120 deg.F. and on no account to more than 140
deg.F.--_overheating will ruin the Stock Solution_--let it stand for
half an hour, then test with a strip of glass. This should show a
perfectly clear golden yellow colour (turning blue in 45 secs.
approx.), free from spots. If dark spots show, this indicates
undissolved indigo, therefore gradually add hydrosulphite solution
(2-3 fluid ozs.). Wait 15 mins. and test with glass strip; if
incorrect continue this every 15 minutes until the glass indicates
clear yellow. If the Stock Solution is greenish white and turbid,
undissolved _indigo white_ is present. Add then not more than a
teaspoonful at a time caustic soda solution until the Stock Solution
answers the glass test.

The _Dye Vat_ should contain about 10 gallons of water heated to hand
hot, 120 deg. and not above 140 deg.F. Add 3 ozs. of hydrosulphite
solution stirring carefully, let it stand for 20 minutes; this renders
harmless any undissolved oxygen. Add a small cupful of the Stock
Solution, stir carefully without splashing. The vats should be greenish
yellow and _should not feel slimy_, an indication of too much caustic.
The vat is now ready to dye and is kept at 120 deg. to 140 deg.F.

Between dips add Stock Solution as required, if the vat goes blue and
turbid add 3 to 4 fluid ozs. of hydrosulphite and warm up to 140 deg.F.
and wait 30 minutes. As a last resort add caustic soda solution very
gradually. This should not be required if the Stock Solution is
properly prepared.

Start to dye with weak vats, 20 to 40 minute dips, and finish with
stronger vats. The more dips given to obtain a fixed shade, the faster
will be the yarn to washing and rubbing. The yarn must be oxidized by
exposure to the air for the same length of time as dipped. After the
final dip, pass the yarn through a 10 gallon bath of water to which is
added 3 ozs. of sulphuric acid, pure or hydrochloric. This neutralizes
the caustic used. Wash yarn at least twice in water.

_Improvement of Defective Indigo Vat Dyes._

If, after washing until clear, the yarn should rub off badly, ther