the Relative Affinities of certain Acids, 563 



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

 acts like a free acid. Thus, when a solution of potassium 

 binoxalate or quadroxalate is added to one of sodium sulphate, 

 sulphuric 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 

 quantity of this latter acid. Carbonic acid is still weaker 

 than these. Ostwald, 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 

 carbonic 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 gradually applied to the bicarbonate. In the second trial 

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

 ultimately shattered with violence. The leg containing the 

 test liquid and sulphate had been secured in a clamp and re- 

 mained uninjured. The liquid therefore had been subjected 

 to the action of carbonic anhydride at a high pressure — it, 

 however, gave no indications of a separation of traces of sul- 

 phuric acid under its action. It is to be remarked that this 

 test is more decisive than if a solution of sodium sulphate had 

 been used and had been tested afterwards. For in this last 

 case, on release of the pressure, the reaction might readily be 

 reversed with recombination of sulphuric acid, had any been 

 liberated. But with the test liquid present during the pressure 

 this reversal could not take place. 



Carbonic anhydride, therefore, does not even under pressure 

 set free any portion of sulphuric acid from sodic sulphate. 



The reactions described in this paper indicate : — 



1. That when to free sulphuric acid a salt is added in 



sufficient quantity to cause the whole of the sulphuric acid to 



saturate itself with the salt-base, it is possible by means of 



the herapathite test to determine the exact point of such 



