436 MORBID PRODUCTS. 



phates and carbonates combined with organic (albuminous, ex- 

 tractive, and fatty) matters. 



In the analysis of mixed concretions we proceed in the 

 following manner : 



A. We incinerate a portion in a platinum crucible, and 

 analyse the residue ; if it burns white easily, the infusible earths 

 preponderate ; if it is difficult or impossible to obtain a white 

 residue, and the ash remains fused and blackish, then the 

 fusible earths or the alkalies preponderate. The residue may 

 consist either of (1) earthy phosphates alone, which may be re- 

 cognized by the rules given in 2, 0, b, and c, or of (2) earthy 

 phosphates and carbonates, the latter originating from earthy 

 urates, or oxalate of lime. (In this case we recognize the pre- 

 sence of earthy carbonates (or of caustic earths, if the heat has 

 been too intense and prolonged), by the rules laid down in 2, 

 dj e, and h.) 



4. The residue may consist of earthy phosphates and car- 

 bonates, and alkaline carbonates, if alkaline urates occur in 

 the concretion. In order to detect the alkaline carbonates, 

 the residue must be pulverised and extracted with water; on 

 the evaporation of the decanted water the alkaline carbonates 

 will remain, and may be recognized by the rules given in 2, f t 

 and g. The portion insoluble in water is readily dissolved in 

 dilute hydrochloric acid, usually with a slight effervescence. 



Ammonia precipitates the earthy phosphates from this so- 

 lution ; after filtration oxalate of ammonia throws down the 

 lime, and after a second nitration phosphoric acid and ammonia 

 cause a precipitation of the magnesia. 



5. Silica may be easily recognized by the rule given in 2, k. 



B. The portion consumed and expelled by exposure to heat, 

 consists of uric acid, of urate of ammonia, of the oxalic acid of 

 oxalate of lime, which is converted into carbonic acid, of the 

 carbonic acid of carbonate of lime, which is expelled at a high 

 and prolonged temperature, of cystin, of ammonia yielded by 

 ammoniaco-magnesian phosphate, of cholesterin or other fats, 

 of bile-pigment, bilin, extractive matters, or other animal or 

 vegetable substances mechanically entangled, as mucus, albumen, 

 or vegetable fibre. 



We may convince ourselves of the presence of uric acid by 



