174 THE MICROSCOPIST. 



lets consist of chloride of sodium ; the more plumose crystals 

 are probably phosphate of soda. 



Fig. 53. 



The Earthy Salts which form the insoluble portion of the 

 ash, and which usually amount in healthy urine to about 1 

 part in 1000, consist of the phosphates of lime and magnesia, 

 together with a small trace of silica. These appear to be re- 

 tained in solution in the urine by the small exoess of acid 

 (probably phosphoric) usually present, and may be precipitated 

 from it by supersaturating with ammonia. The precipitate 

 thus formed consists of a mixture of phosphate of lime, and 

 the double phosphate of ammonia and magnesia, which is 

 also called triple phosphate. These, with the abnormal ingre- 

 dients found in morbid urine, &c., will be treated of when we 

 come to the examination of urinary deposits. It must be 

 borne in mind, however, that a spontaneous precipitate of 

 earthy phosphates is not of itself a proof that they are present 

 in excess, for when the urine is acid, as in health, a considera- 

 ble quantity may be retained in solution, while if it be neutral 

 or alkaline, a comparatively small proportion may be precipi- 

 tated. 



