To Make Extract Of Indigo

1 lb. oil of vitriol (pure, not commercial).

2 oz. finely ground Indigo.

1/2 oz. precipitated chalk.

Mix a little of the indigo with a small quantity of oil of vitriol,

add a little chalk and stir well. Go on mixing gradually till all is

used up. This should take an hour or two. Stir a few times each day

for 4 or 5 days, adding about 1/2 oz. more of chalk by degrees. It is

best mixed in a glass stoppered bottle or jar, and stirred with a

glass rod. It must be kept from the air.