S. L. Penfield — Sulphostannate of Silver from Bolivia. 451 



gave no indications of a separation of traces of sulphuric 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 re- 

 lease 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 re- 

 versal 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 : 

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

 sufficient quantity to cause the whole of the sulphuric acid to 

 saturate itself w T ith the salt-base, it is possible by means of the 

 herapathite test to determine the exact point of such satura- 

 tion. At this point there will necessarily be as much of the 

 acid at first combined with the base, now free in the solution, 

 as corresponds to one molecule of a bibasic acid, that is two of 

 a monobasic acid, half a molecule of a quadrobasic acid, etc. 

 From this we can deduce the exact nature of the resulting 

 equilibrium. 



2. That a series of equilibria thus obtained with different 

 salts, enables us to determine the comparative strength of the 

 affinities of the acids of those salts. 



3. That the fact, already proved in other ways, that even 

 small quantities of weak acids, added to sulphates will set free 

 a certain quantity of sulphuric acid, can by means here given 

 be for the first time rendered visible to the eye by a well 

 marked chemical reaction. 



Art. LVI. — On Argyrodite and a new Sulp/wsta?inate of 

 Silver from Bolivia • by S. L. Penfield. 



List the August number of this Journal, 1893, page 107, the 

 author described as a new species a germanium mineral from 

 Bolivia, to which the name canfieldite was given. It was 

 shown that the mineral was identical with argyrodite in chem- 

 ical composition, but differed apparently in crystallization, 

 canfieldite being isometric while argyrodite was monoclinic, 

 according to the description of Weisbach.* The discovery of 

 the isometric mineral was communicated by letter to Professor 

 Weisbach, and soon after the publication of the author's article 

 a reply was received from him, in which it was stated that 



* Jahrb. f. Min., 1886, ii, p. 67. 



