ARGOL, or ARGAL. (Fe., Tartre brut ; Gan., Weinstein2,—Argol is the crude tartar which, after the fermentation of wine, is deposited on the sides of the cask, along with tartrate of lime, colouring matter, &c., in a thick crust which may be easily detached. It is composed chiefly of bi-tartrate of potash or cream of tartar, but contains also varying proportions of hi-tartrate of lime; it is red or white according to the colour of the wine.
It is from argol obtained in this way that the refined cream of tartar and the tartaric acid of commerce are chiefly prepared (see Tartaric Acid). The neighbourhood of Montpellier, in France, is the chief centre of the manufacture of cream of tartar, which is carried on in the following manner :—Tho crude tartar, after being reduced to powder, is dissolved in water contained in large vats, and heated to the boiling point. The water is kept at this heat for two or three hours and then allowed to cool and to stand for a day or two, at the end of which time the clear liquor is run off from the impure sediment at the bottom into wide-mouthed earthen vessels. The bi-tartrate, partly freed from colouring matter and other impurities, is then deposited in a thick bed of crystals. In order that these may he further purified they are once more dissolved in boiling water, in which has been placed, for every hundred parts of salt, eight or ten parts of a mixture of clay and animal charcoal. The whole is boiled down until a thin film appears on the surface. It is then run into
conical vessels and allowed to stand for eight days, or longer, according to the temperature. The alumina contained in the clay forms, with the remaining colouring matter, an insoluble compound which is deposited along with the animal charcoal at the bottom of the vessel, the sides of which become covered with beautiful, colourless crystals of pure bi-tartrate. These are left for some days on sheets in the open air to be dried and whitened by exposure to the sun.
Cream of tartar is largely used for the manufacture of tartaric acid and the tartrates. The dyer employs it as a mordant for fixing colours on woollen materials. Mixed with whiting, it is much used for cleaning silver. In medicine, it acts as a mild purgative, but when used for this purpose, owing to its very sparing solubility in water, it is usually mixed with a quarter of its weight of powdered boric acid which renders it easily soluble.