218 PHILOSOPHICAL TRANSACTIONS. [ANNO 1797. 



(16) Caustic vegetable alkali acquires a slight tinge from a fragment of this 

 kind of stone, but will not dissolve it. When powdered it is thereby purified from 

 any quantity of lithic acid that it may contain. Phosphoric acid will then dissolve 

 out the phosphorated lime, and the remainder, after being washed, may be decom- 

 posedby the vitriolic acid. The affinity of this acid for a certain proportion of lime is 

 superior even to that of acid of sugar; selenite is formed, and the acid of sugar 

 may be crystallized, and by the form of its crystals recognized, as well as by every 

 other property. It is easily soluble, occasions a precipitate from lime water, and 

 from a solution of selenite, and with mineral alkali forms a salt that requires a large 

 quantity of water for its solution. 



(17) When the stone has been finely powdered, marine acid will slowly dissolve 

 all but any small quantity of lithic matter which it may contain. After the solu- 

 tion has been evaporated to dryness, no part is then soluble in water, the marine 

 acid being wholly expelled. When the dried mass is distilled with a greater heat, 

 the saccharine acid is decomposed, and a sublimate formed, still acid and still 

 crystallizable, but much less soluble in water, and which does not precipitate lime 

 from lime water. After distillation, the remainder contains phosphorated lime, 

 pure lime, and charcoal; and when calcined in the open air, the charcoal is con- 

 sumed, and the whole reduced to a white powder. The 2 former may be dissolved 

 in marine acid, which when evaporated to dryness will be retained only by the 

 lime ; so that water will then separate the muriated lime, and the phosphorated 

 lime may afterwards be submitted to the usual analysis. 



Bone- earth calculus. — Beside that of Scheele, and the 2 already noticed, there 

 is also a 4th species of calculus, occasionally formed in the bladder, distinct in its 

 appearance, and differing in its component parts from the rest; for it consists entirely 

 of phosphorated lime. Its surface is generally of a pale brown, and so smooth as 

 to appear polished; when sawed through, it is found very regularly laminated; and 

 the laminae in general adhere so slightly to each other, as to separate with ease 

 into concentric crusts. In a specimen with which I was favoured by Dr. Baillie, 

 each lamina is striated in a direction perpendicular to the surface, as from an 

 assemblage of crystallized fibres. The calculus dissolves entirely, though slowly, 

 in marine or nitrous acid, and, consisting of the same elements as earth of bones, 

 may undergo a similar analysis, which it cannot be necessary to particularize. By 

 the blow-pipe it is immediately discovered to differ from other urinary calculi: it 

 is at first slightly charred, but soon becomes perfectly white, still retaining its 

 form, till urged with the utmost heat from a common blow-pipe, when it may at 

 length be completely fused. But even this degree of fusibility is superior to that 

 of bones. The difference consists in an excess of calcareous earth contained in 

 bones, which renders them less fusible. This redundant portion of lime in bones 

 renders them also more readily soluble in marine acid, and may, by evaporation 

 of such a solution, be separated, as in the last experiment on mulberry calculus. 

 The remaining phosphorated lime may be re-dissolved by a fresh addition of marine 



