this acid dissolves a small quantity, and forms a triple compound, an _aceto-tartrate of lead_;[356] and since no cyder, or perhaps wine, is wholly destitute of vinegar, it necessarily follows that if the liquor has been once contaminated during the first stages of fermentation, it is impossible for it ever to become entirely pure, except by processes which would render it unfit for drinking.[357] It has very lately been discovered, that _Gallic acid_ and _tannin_ are capable of combining with lead in solution, and of forming a perfectly insoluble substance, which falls to the bottom of the cask; hence all liquors which have been kept in oak casks, for a certain time, must be freed from lead. This explains a fact with respect to the effect of new rum in the West Indies, of some importance. This spirit, when newly distilled, is found to contain traces of lead, derived from the leaden rims of the coppers, and the leaden worm, used for its condensation; but, by keeping about twelve months in oaken casks, it loses its deleterious properties, and no longer exhibits any traces of this metal.[358] Another source, from which acescent liquids may contract saturnine impregnation, is afforded by the metallic glazing of earthenware[359]; that for instance of the common _cream coloured_ ware is composed of an oxide of lead,[360] and is accordingly easily acted upon by vinegar, and saline compounds; jars and pots of this description ought therefore never to be used for preserving pickles, jellies of fruits, marmalade, and similar conserves. For the same reason, _Sir George Baker_ protests against the custom of baking fruit tarts in such ware.[361] _Stone ware_ is glazed with muriate of soda, and is therefore not liable to such an objection.[362] The custom which prevails in some parts of England of keeping milk in leaden vessels, is extremely improper; _Dr. Darwin_[363] has illustrated this subject by the following case; “A delicate young girl, the daughter of a dairy farmer, who kept his milk in leaden cisterns, used to wipe off the cream from the edges of the lead, and frequently, as she was fond of cream, licked it from her finger. She was seized with the saturnine colic, and semi-paralytic wrists, and sunk from general debility.” We are informed by _Mr. Parkes_,[364] that in Lancashire the dairies are furnished with milk-pans made of lead; and that when he expostulated with some individuals on the danger of this practice, he was told that _leaden_ milk pans throw up the cream much better than vessels of any other kind.