URIC acid This acid was discovered by Scheele in the year 1776. It was at first called lithic acid. It constitutes one of the component parts of urinary calculi, and is also found in human urine. There is one species of calculus which is almost entirely composed of this substance ; it is that species which resembles wood in ap pearance and colour. This acid is insi pid, inodorous, almost insoluble in cold water, and soluble only in about 360 parts of boiling water. It separates from this when it cools, into small yellowish crys tals. The solution in water reddens the tincture of turnsole. There is scarcely any action between the uric acid and the sulphuric and muriatic acids. It is solu ble in the concentrated nitric acid, to which it communicates a red colour. It would appear that in this change of co lour the nature oldie acid is also chang ed, for part of it is converted into oxalic acid. Oxymuriatic acid very readily acts upon uric acid, either by suspending a calculus in the liquid acid, or, which is easier, by passing a stream of oxymuriatic acid gas through water, at the bottom of which is placed the uric acid in powder.
Its colour becomes pale, the surface swells up, it softens, and is at last convert ed into a jelly. This part disappears, and is soon dissolved, giving a milky colour to the liquid. There is extricated, by slow efferverscence, small bubbles of car bonic acid gas. The liquid by evapora tion gives inuriate of ammonia, acidulous oxalate of ammonia, both crystallized, nmriatic acid, and malic acid. Thus the oxymuriatic acid decomposes the uric acid, and converts it into ammonia, car bonic, oxalic, and malic acids. Various facts show that uric acid is a compound of a very peculiar kind, formed of azote, of carbon, of hydrogen, and oxygen, and susceptible of a great number of different changes by chemical agents.