450 M. G. Lea — Relative Affinities of certain Acids. 



of herapathite which crystallize out. Solution of sodium sul- 

 phate not containing acetic acid gives no such reaction with 

 the herapathite test. It dries up to a pale yellow residue. 



Acids vary very much in their ability to detach sulphuric 

 acid from sodium. The following acids when added to sodium 

 sulphate and tested by the herapathite test, give the results 

 here noted. 



Malic acid, gives an abundant crystallization. 



Succinic acid, acts similarly. 



Lactic acid, a moderate reaction. 



Mucic acid, about the same as lactic. 



Yanadic acid, traces. 



Arsenic acid, abundant crystallization. 



Hippuric acid, distinct traces. 



Salicylic acid, distinct crystallization. 



Of course the stronger organic acids, tartaric, oxalic and 

 citric separate sulphuric acid with abundant crystallizations of 

 herapathite when they are made to act on sodium sulphate and 

 the test is applied. It was observed that an acid oxalate acts 

 like a free acid. Thus when a solution of potassium binox- 

 alate or quadroxalate is added to one of sodium sulphate, sul- 

 phuric acid is detached precisely as if free oxalic acid had 

 been used. 



It is clear that extremely weak acids such as hippuric and 

 salicylic are able to take a certain quantity of base even from 

 so strong an acid as sulphuric, setting free a recognizable quan- 

 tity of this latter acid. Carbonic acid is still weaker than 

 these. Ostwalcl in determining the relative affinities of acids 

 by the rate of the decomposition of acetamide and by the 

 inversion of cane sugar found no appreciable effect from car- 

 bonic acid. It therefore became of interest to ascertain if any 

 sensible decomposition of sodium sulphate would result from 

 the action of this acid. 



Perfectly pure carbonic anhydride was passed for a long 

 time through a solution of sodium sulphate without setting 

 free a recognizable trace of sulphuric acid. This was expected, 

 the experiment was only preliminary to its repetition under 

 pressure. 



For this purpose sodium sulphate with the test solution was 

 placed in one leg of a bent tube, in the other leg was placed 

 sodium bicarbonate ; and the tube was sealed. Heat was grad- 

 ually applied to the bicarbonate. In the second trial the 

 pressure was raised so high that the stout glass tube was ulti- 

 mately shattered with violence. The leg containing the test 

 liquid and sulphate had been secured in a clamp and remained 

 uninjured. The liquid therefore had been subjected to the 

 action of carbonic anhydride at a high pressure — it however 



