64 PROCEEDINGS OF THE AMERICAN ACADEMY. 



It may be remarked that the purest specimen (Preparation II.c) 

 gave an average result which is very close to the average of all the 

 specimens. 



Silver. — A number of different preparations of this metal, which 

 served as one of the fundamental standards of reference, were used 

 during the course of the work. For the final experiments pure 

 argentic chloride remaining from earlier work was reduced by means 

 of pure sodic hydrate and invert sugar, the invert sugar having been 

 prepared in the first place by heating a strong solution of the purest 

 obtainable cane sugar with a little hydrochloric acid at 100°. After 

 a very thorough washing the metal resulting from this reduction was 

 fused upon hard-wood charcoal in the flame of an ordinary blast lamp, 

 and divided into two parts. 



One half of this silver was purified at once by electrolysis accord- 

 ing to the manner described in a former paper,* and was used in 

 Analyses 30, 31, 32, 35, 36, and 37. The other half was dissolved in 

 the purest nitric acid, and precipitated again with hydrochloric acid; 

 then the argentic chloride was digested with aqua regia, very thor- 

 oughly washed with water, and again reduced to the metal. The last 

 product was fused into large buttons upon sugar charcoal, and puri- 

 fied by electrolysis as before. The current obtained from seven or 

 eight gravity cells is amply sufficient for the purpose. This doubly 

 refined silver was used in Experiments 33, 34, 38, 39, 40, 41, and 43. 



The silver used in Experiment 42 was prepared in the first place 

 by Mr. H. F. Brown, according to the cuprous amnionic sulphite 

 method of Stas.f Although the substance thus prepared gave every 

 outward evidence of perfect purity, it was once again purified, this 

 time by means of the electrolytic method used in the case of the 

 previous specimens. 



* These Proceedings, XXVIII. 22. 



t Untersuchungen, etc. (Aronstein), pp. 34 and 113. 



