MADDER.

291

pyrolignite of iron is prepared with pyroligneous acid deprived by distillationof the greater part of the tarry matters, and is of a strength of io° Baume,

= sp. gr. 1-075.

The following mordants are for purples thickened with British gum

Purple 8.

Boiling water .48 litres

Pyrolignite of iron at 10° Baume .. 6 „

British gum.36 kilos.

Oil of turpentine.375 grms.

Purple 32.48 litresi£ ..

30 kilos.375 grms.

Purple 10.—2 parts of purple 32 and 22 parts of purple 8.

Purple 12.—4 parts of purple 32 and 20 parts of purple 8.

Purple 16.—8 parts of purple 32 and 16 parts of purple 8.

For Black :—

Pyrolignite of iron at 10° Baume.32 litres

Calcined starch. 10 kilos.

Water.24 litres

Quercitron liquor at i8 a Baume (sp. gr. 1-143) .. .. 2 ,,

Logwood decodtion at 17° Baume (sp. gr. 1-134) •• 2 „

Olive oil . i litre.

In former times it was the custom to add to the black mordant destined forblock printing a salt of copper, chiefly the acetate, probably for aiding theready combination of the oxide of iron with the cloth. Since M. Schlum-berger observed that arsenite of copper and lime (15 grms. of each for 1 litreof mordant) has the effedt of very particularly favouring the combination ofoxide of iron with the cloth, it became the custom to add to mordants forpurple a preparation known as the copper solution for purples, prepared with—

Lime water . 48 litres

White arsenic (arsenious acid) .750 grms.

Sulphate of copper. . 750 ,,

The whole is boiled, and allowed to settle before being used. The use of thiscopper solution for purple mordant has been dispensed with, because its utilitywas not quite proved. The adtion of salts of copper in these mordants ischiefly beneficial with pure solutions of per-salts of iron, and especially when themordants are thickened with gum Senegal. When other thickeners are used,and other solutions of iron, the pyrolignite for instance, there is no perceptibleadvantage in the use of a copper solution.

The mordant for purples known in this country as iron liquor, or blackbfluor, is made by steeping old iron of all sorts—such as hoops, worn out tin-plate, &c.—in warmed wood vinegar, or pyroligneous acid, obtained by thedestructive distillation of wood. By continually moving the acid, and keepingup a moderate heat, it becomes saturated with iron in a few days, crude acetateof iron being formed. The iron liquor is met with in commerce as a fluidblack by refledted light, but in thinner layers it is seen to possess a greenish-olivecolour. Its taste is inky, and since the crude acid used in its preparation isnot quite free from tarry matters the liquor has a peculiar smell. Its strengthis from 18 0 to 28° Tw. (sp. gr. respedtively rogo and 1-140).

Iron liquor at about 6° Tw. (sp. gr. 1-030) gives with madder, properlythickened (upon which much depends for the success of first-class styles ofwork), black ; from 4 0 (sp. gr. ro2o) downwards to a very diluted state it gives

u 2