ANALYSIS. 217 



cium and triple phosphate. If it is combustible it consists 

 of organic compounds. 



Blackening when ignited is evidence of organic mat- 

 ter, but if slight it may be merely mucus arising from 

 irritation of the bladder, and not an essential part of the 

 calculus. Ignition on the foil will divide the constituents 

 into two classes, although both may be present. 



COMBUSTIBLE, OK INCOMBUSTIBLE, OR 



ORGANIC. INORGANIC. 



1. Uric acid. 1. Calcium phosphate. 



2. Ammonium urate. 2. Calcium oxalate. 



3. Calcium carbonate. 



4. Triple phosphate. 



5. Urates of K, Na, and Ca. 



If it is composed largely or entirely of organic matter 

 try the murexid test (Experiment 354) for uric acid and 

 urates. If inorganic compounds are present, powder a piece 

 and treat in a test-tube with 2 or 3 cubic centimeters of 

 dilute hydrochloric acid. Carbonates dissolve with effer- 

 vescence of carbon dioxid gas, the others without. Warm, 

 if necessary. Filter, if it does not give a clear solution. 

 To one-fourth of the filtrate in a test-tube add sodium 

 hydrate until it is alkaline, and test for ammonia by hang- 

 ing in the tube a strip of moist red litmus-paper, being 

 careful that it does not touch the side of the tube which 

 is wet with the sodium hydrate. The tube can be allowed 

 to stand corked over night or the ammonia-gas can be ex- 

 pelled from the liquid by boiling. If present it will turn 

 the paper blue. 



To the remainder of the solution in hydrochloric acid 

 add ammonia until it is alkaline, acidify with acetic acid, 

 and boil. If there is a precipitate, filter. 



