524

DYEING AND CALICO PRINTING.

that the liquid is bottled off when the required strength has been reachedwithout pushing it on to crystallisation. Some makers, instead of applyingheat to promote the adtion of the hydrochloric acid upon the mass of featheredtin, pour on the acid, and after a few minutes run it off upon another similarquantity of tin. In a short time it is returned to the first lot, and by thisalternating adtion the temperature is raised and the tin dissolved much morerapidly than if the acid were allowed to adt without intermission upon onequantity of tin. In some establishments it is customary to use the hydro-chloric acid at the strength of 32 0 Tw., whilst in others it is diluted with moreor less water before being allowed to adt upon the tin. In consequence, twosamples of genuine double muriate, of the same specific gravity, but fromdifferent makers, may contain unlike amounts of tin. The lower the initialstrength of the acid, the more metal must have been dissolved to raise thespecific gravity to any given point.

Double muriate is frequently adulterated with sulphuric acid, sulphates ofzinc and magnesia, chloride of zinc, &c. The price at which many samplesare offered is in itself a sufficient proof of sophistication, being frequentlyless than the market-price of the tin which ought to be present in the genuinearticle. Few samples are met with which do not contain sulphuric acid inlarger amount than can be accounted for by the possible presence of a little ofthis body as an impurity in the hydrochloric acid used.

The methods for detedting these various sophistications have been indicatedabove. The weaker double muriates, from 70° to 90° Tw., are used by thewoollen-dyers; the stronger, at no 0 to 120°, are applied to cotton, which isless able to resist the adtion of acids.

Single Muriate of Tin is comparatively little used. Its specific gravityranges from 40° to 6o° Tw., and its proportion of metallic tin varies from 1 to2 ounces per lb. It is chiefly employed in wool-dyeing.

II. Solutions of Proto-Salts of Tin , in which other Acids are used along withthe Hydrochloric .

Old Scarlet Spirit (Dr. Bancroft’s).

Mix—Oil of vitriol .. lbs.

Hydrochloric acid, at 32 0 Tw...3 ,,

And dissolve in the mixture—

Tin .14 ozs.

This spirit was, as its name implies, formerly used for lac and grain scarletsupon woollen and worsted goods. It is now little used, as the scarlets producedby its means are apt to exhibit a brownish shade.

Amaranth Spirit.

Mix—Hydrochloric acid, at 32 0 Tw.95 lbs.

Oil of vitriol . 5 >»

And dissolve—

Tin .4 ,, 11 ozs.

This spirit is greatly recommended by some woollen-dyers for producingreddish-violet and purple shades with the woods.