URINARY CONCRETIONS. 1055 



anhydrous, and contains 1 atom of cystic oxide and of the acid. 

 The nitrate contains 2 atoms of water, one of which it loses 

 at 105. The solution of cystic oxide in an alkali or alkaline 

 carbonate is decomposed by heat, ammonia first coming off, and 

 then as the evaporation proceeds, a combustible gas, which 

 smells like sulphuret of carbon. This calculus contains sulphur, 

 and is represented by C 6 NH 6 O 4 S 2 (Thaulow). 



3. Oxalate of lime, or mulberry calculus, has a dark-coloured 

 tuberculated surface, is very hard and compact, rarely large. 

 It is easily distinguished by the circumstance that its powder 

 does not dissolve in acetic acid ; but after being heated on a 

 spatula to low redness, in the flame of a spirit-lamp, it dis- 

 solves readily in that acid with effervescence, the oxalate of 

 lime having been converted into carbonate. The composition 

 of crystallized oxalate of lime is CaO,C 2 O 3 + 2HO. 



4. Bone-earth calculus ; its surface is pale brown and quite 

 smooth, as if it had been polished. It is compact, and 

 when sawed through, appears very regularly laminated. It is 

 distinguished by its powder dissolving in dilute nitric and 

 hydrochloric acid, but not in acetic acid, nor in solution of 

 caustic potash. It appears white and not easily fused before 

 the blow-pipe. The composition of bone-earth is expressed by 

 8CaO,HO + 3PO 5 . 



2. Ammonmco-magnesian phosphate calculus is composed of 

 the phosphate of magnesia and ammonia, which precipitates 

 in granular crystals when phosphoric acid is added to a mixed 

 solution of a salt of magnesia and ammonia (page 508). It is 

 white and less compact than the last, and sparking crystals of 

 the salt are often perceptible in the mass. It emits ammonia 

 when heated to 212, is dissolved by cold acetic acid and pre- 

 cipitated again on neutralising the acid. It emits ammonia 

 when digested in a solution of potash, but does not dissolve. 

 It fuses into a white pearly globule by strong heat of the blow 

 pipe. The composition of crystallized phosphate of magnesia 

 and ammonia is 2MgO.NH 4 O,PO 5 + 14HO. 



6. The fusible calculus is a mixture of the two last, is com- 

 mon in old and exhausted subjects, and often attains a large 

 size. It is commonly white, rather friable and chalky ; its 

 fracture rugged and uneven, and surface dusty. It melts easily 



