The urat of ammonia was first discovered by Fourcroy: it differs little in appearance from the acid, except that its laminae arc less sensibly streaked. It sometimes forms the whole of a calculus. It is scarcely soluble in water, except with excess of ammonia, and is decomposed by all the acids, rapidly by the fixed caustic alkalis.

The urat of soda was first discovered by Mr. Ten-nant in arthritic concretions, but is not an ingredient in urinary calculi. It consists of friable fragments, without any regular arrangement, and certainly combines some animal and gelatinous matter.

Phosphat of lime is a very frequent component part of urinary concretions. It appears in three different forms, viz. a granulated, bony substance, susceptible of a fine polish, like the pretended calculi of the pineal gland, the salivary, lachrymal, or bronchial glands; secondly, in thin strata, which are concentric and of a dead white, friable like the urinary calculi themselves: thirdly, of a more uniform texture like ivory. This ingredient is not affected by acids; and, with the blowpipe, exhales the smell of animal matter, becoming white and friable. It is soluble in the nitric and muriatic acids, but insoluble in the vitriolic. The solutions afford also a calcareous oxalate, from which the existence of the lime is ascertained.

The acid phosphat of lime is chiefly confined to the bezoars, of which it is the principal substance. It is formed in thin strata, with little adhesion, and very brittle. In fusion it gives out a slight aromatic odour.

The ammoniaco magnesian phosphat is most easily recognised among the ingredients of calculi, though for a long time unknown. It sometimes occurs in white prismatic crystals, semitransparent, or in tables whose edges project, and form the little points on the surface of some urinary calculi, as well as on the intestinal bezoars of the elephant and the horse. At other times it is in sparry, lamellated strata, semitransparent, of different thickness, covering another primitive calculus, consisting of the uric acid, or some other body. The resemblance to calcareous spar is so strong, that Dau-benton and Vicq. dazyr had nearly confounded it with this fossil. This salt is smooth to the eye and to the touch, easily reduced to a white light powder of a sweetish, insipid taste, without the dryness of phosphat of lime. This ingredient is easily dissolved in acids and alkalis, but contains some animal matter; and, when decompounded, leaves some soft, light, transparent, membranous flakes, more nearly approaching the primitive forms of the calculous fragments than those from the phosphat of lime, which also contains, though less strongly marked, similar membranous substances. It generally forms the external strata of urinary calculi, and the greater proportion of the intestinal bezoars of the horse, the elephant, and the larger mammalia; but is never discovered in their urinary calculi. After having been ascertained in the analysis of calculi, it was found in the urine; at first in the form of the magnesian phosphat, and, when the urine began to purify.

Rr 2 in that of the ammoniaco magnesian phosphat. This is the triple salt, formed in hexaedral prisms on the sides of the vessels in which urine has been suffered to stand, till it undergoes a spontaneous decomposition.

The oxalate of lime long eluded the investigation of chemists; but it is constantly found in the mulberry calculi, so called from their resembling that fruit in colour and pointed projections. This substance is hard like ivory; and, when sawed, exhales the faint odour of bones rubbed against each other. It consists of concentric laminae applied in rounded scales, or like caps; which, successively covering each other, produce the projecting points. It contains an animal jelly, and is exclusively discovered in human urinary calculi.

Carbonate of lime, long supposed to be the only basis of the human urinary calculi, is not found in them. It only occurs in the urinary calculi of the other mammalia, particularly, horses, oxen, and pigs. It is neither in strata nor in crystals, but in confused irregular masses, consisting of granulated molecules.

Flint occurs very rarely. M. Fourcroy only found it twice in six hundred calculi, and then in small quantities, mixed with other substances. It is apparently accidental.

The spermaceti Fourcroy calls' adipocire, as a medium between fat and wax, but not perfectly the same with that from the whale, as it is more dry and fusible. This substance often occurs in pure white, shining, talcy laminae, or covered with a brown colouring matter. It is sometimes found only like little straws, passing through these concretions, occupying their centre, or deposited, on cooling, by the alcohol, in which the calculi have been immersed. It is soft and fat to the touch. When rubbed and warmed, the smell resembles that of suet, or the spermaceti of the whale: it is very light and swims on water. It is fusible in nearly the same temperature as the spermaceti, resembling, when melted, a yellow oil. It sublimes, like wax, at a temperature above its melting point. By distillation it affords water and acetous and sebacic acids, as well as carbonated hydrogenous gas. Its kind of fusibility renders it less readily decomposed in an open fire than fat. It is not affected by acids, but forms a soap with alkalis. It is insoluble in water, soluble in alcohol, and in a larger proportion in hot than in cold spirit. The solution of the adipocire separates in shining crystals when cooled, and is decomposed by the addition of water. It dissolves in fixed oils, and in volatile ones slightly warmed. It is found only in the biliary calculi of men; often separate and pure in those calculi which are white and crystalline. It is not discovered in the biliary calculi of the ox and other mammalia hitherto examined.

The animal bezoardic resin we have already noticed, as much as its importance in this work merits.