ANALYTICAL EVIDENCE. 



311 



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 XXXIII. P. 131. 



COMPOSITION OF OXALIC, OXALURIC, AND PARABA- 

 NIC ACIDS. 



1. OXALIC ACID (hydrated). 



Gay Lussac & Th6nard. Berthollet. 



Carbon . . 26566 25-13 



Hydrogen . 2-715 3-09 



Oxygen . . 70-689 71-78 



Calculated 

 C 2 3 + HO. 



27-04 



2-21 



70-75 



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

 3. PARABANIC ACID, a 



Wohler and Liebig.* 



