444 MORBID PRODUCTS. 



mixed chlorides. The dried residue, after "being weighed, is 

 moistened with a little concentrated hydrochloric acid, and 

 afterwards treated with anhydrous alcohol, which takes up the 

 chloride of magnesium. The alcoholic solution is treated with 

 a little carbonate of potash, evaporated, and dried in a platinum 

 crucible heated to incipient redness. After the extraction of 

 the potash, the magnesia remains. The chlorides of calcium, 

 sodium, and ammonium, must be separated in the ordinary 

 manner. 



III. Calculi of uric (xanthic] oxide. Calculi of this sub- 

 stance usually contain no other constituent, with the exception 

 of a little animal matter. Uric oxide was first met with by 

 Marcet, forming a calculus weighing 8 grains ; some years after- 

 wards a few minute concretions of the same nature were de- 

 scribed by Laugier; more recently it was discovered by 

 Stromeyer in a calculus weighing 338 grains, and as large as a 

 pigeon's egg, extracted by Langenbeck ; [and a fourth specimen 

 weighing 7 grains, has been lately described by Dulk. 1 ] Their 

 external surface is smooth and polished, and of a cinnamon- 

 brown colour. Their cut surface is of a brown flesh-colour, 

 and consists of concentric laminae easily separable from each 

 other. In point of hardness they resemble uric acid, and when 

 rubbed they assume a waxy appearance. Although uric oxide 

 is of rare occurrence, it need never escape detection with or- 

 dinary care. The fact of its entire destruction before the flame 

 of the blow-pipe at once distinguishes it from the calculi which 

 contain fixed constituents : by its behaviour with nitric acid, 

 and with carbonate of potash (in which uric acid dissolves, but 

 uric oxide is insoluble,) it may be distinguished from uric acid, 

 which it resembles in many respects. 



In order to make a full analysis of a calculus of this de- 

 scription, it must be first pulverised, and then everything 

 soluble in ether, alcohol, and water removed. If uric acid is 

 associated with it, carbonate of potash serves to separate the 

 acid from the oxide ; if earthy phosphates or oxalate of lime 

 are present, they must be removed by dilute hydrochloric acid. 

 Any urates that are present are taken up by water. 



1 [Simons' Beitrage, p. 413 : moreover linger has discovered minute traces of a 

 substance closely allied to uric oxide, if not identical with it, in guano.] 



