LEMON, Salt of, a term improperly applied to bin-oxalate of potash, or salt of sorrel. It is prepared, in Switzerland and the neighbouring countries, from wood-sorrel; about 60 or 70 lb. of the mature plant yielding about 5 oz. of the crystallized salt. Some persons, deceived by the vulgar name, have used this substance to acidulate punch; but it is a dangerous practice, for the bin-oxalate of potash is an active poison. It is best known in this country as a means of removing ink-spots from linen. When an ink-spot is washed with an alkaline soap, it forms a yellow iron-mould, as it is called, in consequence of the oxide of iron, which is the basis of the ink, attaching itself to the cloth, while the tannic acid of the ink is removed by the alkali of the soap. The oxalic acid of the bin-oxalate of potash unites readily with most of the metallic oxides; and in the case of an iron mould, forms a colourless oxalate of iron, which being soluble, is readily removed from the linen. (C. T.)