THE EARTHY AND ALKALINE PHOSPHATES. 347 



If to perfectly healthy and strongly acid urine a drop or two of a solution of chlo- 

 ride of calcium is added, no precipitate falls. If the acidity is lessened by any alkali, 

 on boiling a granular precipitate is occasioned. This, when the urine is still acid, 

 is partly or entirely redissolved on cooling ; or if alkaline, immediately dissolves in 

 dilute hydrochloric acid without any trace of effervescence. 



Between three and five hours after food, at which time the earthy phosphates are 

 always in excess, if healthy acid urine which gives no deposit on boiliilg has some of 

 its acidity removed by fixed alkalies, or alkaline phosphate, a deposit takes place on 

 boiling, and this is always granular, the fluid becoming more acid than before. 



If to such alkaline urine as is passed thick from earthy phosphate a little biphos- 

 phate of soda is added, the phosphate redissolves ; and if the biphosphate is not 

 added in excess the earthy phosphates can be precipitated by heat, the reaction be- 

 coming more acid ; but if an excess be added, the fluid remains perfectly clear on 

 boiling. 



There is then the closest coincidence between the deposits of earthy phosphates in 

 some states of the urine, and their deposit from solutions of the phosphates of soda ; 

 and the same method which is followed for obtaining a precipitate of earthy phos- 

 phates dissolved in biphosphate of soda, will give a precipitate from healthy acid 

 urine, and that which hinders precipitation in the one has the same effect on the 

 other. 



The deposit of phosphate of magnesia by boiling was supposed by M. Riffault to 

 depend on the formation of a more basic phosphate of magnesia. The same expla- 

 nation is still more probably the truth regarding the precipitation of the phosphate 

 of lime by boiling, whether from solutions of phosphates of soda or from the urine. 



llie formation of crystalline earthy phosphates when great excess of earthy phos- 

 phate was present while at the same time the biphosphate of soda made the liquid 

 very acid, gives the explanation why crystalline phosphate of lime is so seldom seen 

 in the urine. Still it may occasionally be met with. Crystalline phosphate of mag- 

 nesia, from its greater solubility, can scarcely appear. The amorphous deposit of 

 phosphate of magnesia when urine is boiled may perhaps be recognised by its far 

 greater solubility than the phosphate of lime as the fluid cools. 



In the state of health acid phosphate of soda, mixed probably with common phos- 

 phate of soda, holds the earthy phosphates in solution. No precipitate is occasioned 

 by chloride of calcium. If, after the water is passed or before from medicines, or 

 particular food, or state of body, some of the acid phosphate is converted into com- 

 mon phosphate, a precipitate takes place on boiling the acid urine. If this very 

 rapidly dissolves before the fluid is cold, the precipitate contains most probably 

 phosphate of magnesia ; if very slowly, it is more likely to be phosphate of lime. If 

 the urine be neutral to test-paper, that is, contains still less biphosphate of soda 

 (the common phosphate being decidedly alkaline to test-paper), then the precipitation 



