442 MORBID PRODUCTS. 



yields a residue of hydrochlorate of ammonia, and probably the 

 chlorides of sodium and calcium. In order to separate these 

 substances the dried residue is first weighed, and then dissolved 

 in water; some ammonia, and subsequently oxalate of ammonia 

 are added, in order to precipitate the lime. The fluid after 

 filtration is evaporated, and the dried residue exposed to a 

 strong heat : the chloride of sodium is left, and the chloride 

 of ammonium may be estimated by the loss of weight. The 

 bases are calculated from the lime which is left after the expo- 

 sure of the carbonate of lime to heat, and from the chlorides 

 of sodium and ammonium, and are combined with the uric 

 acid. 



The portion of the powdered calculus not taken up by water 

 is treated with dilute hydrochloric acid, which dissolves any 

 earthy phosphates that may happen to be present. They are 

 precipitated by the addition of ammonia to the acid solution, 

 and must be then collected on a filter, washed, dried, and 

 weighed. The uric acid (the remaining constituent) must be 

 perfectly dissolved in caustic potash, from which it must be 

 precipitated by super-saturation with hydrochloric acid. It 

 must be then washed on a filter, dried, and weighed. The acid 

 solution usually contains a trace of organic matter, (vesical 

 mucus or albumen ;) its presence may be detected by the 

 addition of a little ferrocyanide of potassium, which causes a 

 precipitate. 



II. Calculi of urate of ammonia. This form of calculus is 

 somewhat rare, and indeed its existence was regarded as un- 

 certain till Prout determined the point beyond a doubt. Ac- 

 cording to Fourcroy these calculi are usually small, occur more 

 frequently in children than in adults, have a whitish or clay- 

 colour, a smooth or tuberculated surface, and an earthy frac- 

 ture exhibiting concentric strata. Yellowly found that of 59 

 small stones taken from a man aged 45 years, 24 consisted of 

 urate of ammonia and 35 of uric acid. Urate of ammonia 

 occurs, however, most frequently mixed with other consti- 

 tuents, especially with uric acid : moreover it often forms the 

 nucleus of large calculi, or occurs as a stratum between a 

 nucleus of uric acid and an external coating of phosphates ; in 

 such cases, however, it is not pure but mixed with crystals of 



