URINARY CALCULI. 449 



phosphates are precipitated from this acid solution by ammonia, 

 and after being washed, are exposed to a red heat. Calculi 

 of phosphate of lime and ammoniaco-magnesian phosphate 

 often contain uric acid, the alkaline urates, and sometimes 

 oxalate and carbonate of lime. The alkaline urates are, in that 

 case, extracted with boiling water ; on digesting a portion of 

 the residue in dilute hydrochloric acid, the earthy phosphates 

 are dissolved and the uric acid remains; if carbonate of lime is 

 present, effervescence is observed on treating a little of the pow- 

 dered calculus with hydrochloric acid ; the lime may be precipi- 

 tated by oxalate of ammonia, after the earthy phosphates have 

 been thrown down from the acid solution by caustic ammonia. 

 If oxalate of lime is present, the powdered calculus (the urates 

 having been previously removed) after a short exposure to heat 

 (but not before) effervesces on the addition of hydrochloric 

 acid. The large calculus noticed in page 439 consists princi- 

 pally of earthy phosphates with small quantities of the urates 

 of ammonia and soda lying one above the other in laminae. 

 It contains a nucleus about the size of a nut, of a mulberry 

 appearance, consisting of oxalate of lime, and in the centre of 

 this is a nucleolus of the size of a large pea, consisting almost 

 entirely of uric acid. 



VIII. Calculi of neutral phosphate of lime are very rare : 

 they were first described by Wollaston. Their surface is 

 usually pale brown, and so smooth as to appear polished. On 

 sawing through a calculus of this nature it is found very regu- 

 larly laminated, and the laminse in general adhere so slightly 

 to each other as to separate with ease into concentric crusts. 

 Each lamina is striated in a direction perpendicular to the 

 surface, as from an assemblage of fibres. In these as in all 

 other calculi we meet with a certain amount of animal matter, 

 supposed by Berzelius to be identical with that which is asso- 

 ciated with phosphate of lime when we precipitate that salt 

 from the urine. Hence on heating a portion before the blow- 

 pipe it becomes charred, and evolves an odour of burned horn ; 

 it finally burns white and fuses, which distinguishes it from the 

 basic phosphate of lime, which is infusible before the blowpipe. 

 Since, however, ammoniaco-magnesian phosphate readily fuses 

 before the blowpipe we must examine previously that none of 

 it is present. 



ii. 29 



