NEPHRITIC Stone, a soft, brittle, opaque stone, not susceptible of a good polish; smooth, and, as it were, unctuous to the touch; variegated with several colours, of which green is the principal. It is found in Saxony, Bohemia, Switzerland, Spain, and Mexico; and from the imaginary virtues ascribed to it in nephritic disorders, has been ranked among the precious stones, but differs exceedingly from them in all its sensible qualities. Neumann finds fault with some authors for referring this stone to the jaspers, agates, or marbles; from all of which, he says, it widely differs: it wants the red specks of the jaspers, the hardness and compactness of the others, and all of them want its unctuousity or soapiness. Out of 60 grains of nephritic stone, vinegar dissolved three; oil of vitriol seven; spirit of vitriol 14; spirit of nitre 16; aqua regia 18; and spirit of salt 20. The spirit of salt acquired a greenish-yellow tincture; aqua regia a gold yellow; oil of vitriol a dark-brownish; the other acids remained colourless. Both the marine acid and aqua regia left the undissolved earth whitish; the nitrous acid greyish; the diluted vitriolic acid brownish-yellow; the concentrated light reddish-brown; the ac-
Nephriticous, unchanged. An ounce of this substance powdered, and distilled in a retort in an open fire, yielded about a drachm and an half of phlegm, which had a penetrating empyreumatic smell, but made no change in the colour of the syrup of violets. On distilling four ounces together, there was an appearance of an actual empyreumatic oil, with a saline matter, which was found to be sal ammoniac. The matter remaining in the retort was of a reddish-brown colour. An ounce of the powdered stone, mixed with an equal quantity of fixed alkaline salt, and urged with a strong fire, did not melt, but formed a quite porous mass, in colour inclining to reddish-grey, and weighing two drachms less than the mixture did at first. Dr Lewis tells us, that the nephritic stone is a species of the indurated clays, called, from their unctuousity, steatite. With these it agrees, not only in its obvious properties, but likewise in its burning hard, the peculiar characteristic of argillaceous earths. Its green colour seems to proceed from copper. Pott relates, that on fusion with an equal quantity of borax, it yielded a beautiful red mass resembling an agate, with a grain of copper at the bottom. The nephritic stone is considerably the hardest of all the substances of this class.