RICHARDS AND HEIMROD. — THE IMPROVED VOLTAMETER. 417 



The anodes were bars 5xlXl centimeters of the purest silver, sup- 

 ported by silver wires and not enclosed in filter paper ; and the electro- 

 lyte usually contained ten grams of pure, freshly prepared argentic 

 nitrate in a hundred cubic centimeters of solution. 



The manipulation was simple. The platinum crucibles were cleaned, 

 dried at 160°, and weighed after three or four hours' cooling in a large 

 desiccator kept in the balance-room. In order to prevent leakage during 

 the electrolysis, the several stands were insulated by separate glass plates, 

 and all the connections were air lines. The apparatus was protected, as 

 in the earlier experiments with copper, by a miniature house with walls 

 of fine cotton cloth, which helped to exclude dust. When the current 

 was broken, the electrolyte was removed, the silver was rinsed twice 

 with water, a third filling with water was allowed to stand in the cru- 

 cible for two or three hours, and a fourth one remained in it over niffht. 

 The wash-waters were collected and filtered if the silver showed any 

 tendency to break off. In such cases a Gooch crucible was employed to 

 collect the particles ; and a very small filter, afterwards burned, served 

 to catch the minute flakes of asbestos detached from the mat. On the 

 next morning the crucibles were washed once more, rinsed twice with 

 pure alcohol, and finally dried and weighed as before. This method of 

 treatment gave opportunity for the diffusion of mother liquor from the 

 intricate recesses of the crystallized mass, while it did not run the risk of 

 dissolving silver which may attend the use of boiling water for washing. 



As has been said, the crucibles were dried at 100°. It was subse- 

 quently shown, in agreement with the results of Lord Rayleigh and Mrs. 

 Sidgwick, that a red heat is needed to drive off all the included liquid 

 from the silver crystals; but since the amount included is fairly constant, 

 this fact does not interfere with the availability of the uncorrected data 

 for the present purpose of comparing one weight of silver with another. 



Weighings were made upon the balance which served for the weigh- 

 ings in the earlier work upon copper, — one which has served also for 

 many determinations of atomic weights. Its results with small objects 

 may he depended upon to within ^ milligram. All weighings were made 

 by double substitutions, a similar vessel being used as a tare, and the 

 weights were of course carefully standardized. Since the question con- 

 cerned merely the comparison of silver with silver, the results were not 

 at first corrected to the vacuum standard. 



The results show that the average difference between the weights of 

 the silver deposited in two crucibles placed in series was less than the 

 tenth of a milligram, or only about four parts in one hundred thousand. 

 vol xxxvii. — 27 



