ANALYTICAL EVIDENCE. 321 



An excellent method of detecting the presence of cystic 

 oxide in calculi or gravel is the following : 



The calculus is dissolved in a strong solution of caustic 

 potash, and to the solution is added so much of a solution 

 of acetate of lead, that all the oxide of lead is retained in 

 solution. When this mixture is boiled there is formed a 

 black precipitate of sulphuret of lead, which gives to the 

 liquid the aspect of ink. Abundance of ammonia is also 

 disengaged ; and the alkaline fluid is found to contain, 

 among other products, oxalic acid. 



NOTE (33), p. 137. 



COMPOSITION OF OXALIC, OXALURIC, AND PARABA- 



NIC ACIDS. 

 1. OXALIC ACID (hydrated). 



Gay Lussac & ThSnard. Berthollet. 



Carbon 26'566 25'13 26'66 



Hydrogen ... 2-745 3'09 2'22 



Oxygen 70'689 71'78 7M2 



2. OXALURIC ACID, a 



WohlerandLiebig.* C^Mfc 



Carbon 27'600 27'318 27'59 



Hydrogen 3" 122 3'072 3'00 



Nitrogen 21-218 21-218 21'29 



Oxygen 48-060 48'392 48'12 



a Ann. der Pharm., XXVI., 289. 



3. PARABANIC ACID, a 



WijhlerandLiebig." 



Carbon 31'95 31-940 31'9l 



Hydrogen 2'09 1'876 1'73 



Nitrogen 24-66 24-650 24'62 



Oxygen 41'30 41-534 41-74 



a Ann. der Pharm., XXVI,, 286. 

 Y 



