448 MORBID PRODUCTS. 



solution is super-saturated with ammonia, and the precipitate 

 washed with a weak ammoniacal solution. It is exposed to a 

 red heat, and dissolved in hydrochloric acid ; the earthy phos- 

 phates are then precipitated by ammonia, and the lime sepa- 

 rated from the filtered solution by oxalate of ammonia. In 

 order to analyse the residue insoluble in hydrochloric acid, it 

 must be boiled in caustic potash and filtered; the uric acid 

 and silica must be thrown down by an excess of hydrochloric 

 acid; if the precipitate is washed, weighed, and submitted to a 

 red heat, we obtain the silica as a residue. 



The amount of animal matter, and especially of pigment, 

 is generally larger in these than in any other calculi. The 

 animal matter seems to consist partly of protein-compounds, 

 and partly of extractive matter. Whether the colouring matter 

 is due to the haematin of the blood, or to uroerythrin, has never 

 been determined. 



VII. Calculi of ammoniaco-magnesian phosphate and phos- 

 phate of lime. These calculi are of the most common occur- 

 rence next to those of uric acid. They sometimes attain a very 

 large size; they are usually globular or spheroidal; their colour 

 is white, gray, or dull yellow ; their fractured surface is less 

 earthy than in the preceding calculi, and is interspersed with 

 sparkling crystals; and although in general friable, their texture 

 is occasionally compact and dense. When laminated, which is 

 seldom the case, the intervals between the layers contain glis- 

 tening crystals of ammoniaco-magnesian phosphate. On heating 

 a fragment of a calculus of this nature on platinum foil an odour 

 of ammonia is developed: it does not burn white so readily as 

 the oxalate of lime, since the ammoniaco-magnesian phosphate, 

 if present in any quantity, fuses and produces a grayish white 

 enamel. 



The moistened ash does not affect red litmus paper ; it dis- 

 solves in hydrochloric acid without effervescence, and may be 

 precipitated from it by ammonia. As these calculi contain a 

 little fat and extractive matter, it is requisite in making a 

 careful analysis that, after being pulverized, they should be ex- 

 tracted with ether and alcohol; on dissolving the residue in 

 hydrochloric acid a small amount of flocculent matter is usually 

 observed, arising probably from vesical mucus. The earthy 



