410 PROCEEDINGS OF THE AMERICAN ACADEMY. 



fulfilment of the law under widely varying conditions. But none of 

 these series of experiments yielded results trustworthy within one part 

 in a thousand, and most of them showed deviations of at least one per 

 cent; hence the possibility of slight deviations remained open. 



In the experiments which are described below, a single metal, silver, 

 was deposited in two successive, widely different cells by the same 

 current. The conditions were so chosen as to make possible the elimi- 

 nation or determination of all conceivable side-reactions. 



One of the cells consisted simply in the porous cup voltameter, or 

 coulometer, which has been shown to give consistent and accurate 

 results.* The other was a precisely similar arrangement of apparatus 

 filled with a solution of argentic nitrate in fused potassic and sodic 

 nitrates, maintained at about 250°. 



This mixture of nitrates has a double advantage over pure argentic 

 nitrate as an electrolyte. In the first place, the comparatively small 

 concentration of silver diminishes the danger of accidental reduction, 

 and in the next place, the foreign solvent enables one to determine 

 the amount of mother liquor included in the crystals. The solution- 

 tensions of the alkali metals are so high as to prohibit the electrolytic 

 deposition of a weighable trace of either in the presence of an excess of 

 dissolved silver. 



It is true that this plan of experiment introduced two variables at 

 once into the problem, a proceeding logically incomplete. If a difference 

 were found between the two deposits of silver, further experiments 

 would be needed in order to determine if this difference were due to 

 the change of solvent or to the change of temperature. Such further 

 experiments would have been made if they had seemed necessary ; but 

 the chances against accidental coincidence seemed so great as to elimi- 

 nate any serious danger from the interpretation given below. This is 

 fortunate, for it is not easy to find a single solvent capable of yielding 

 satisfactory results over so large a range of temperature. 



Although all three nitrates were prepared in a state of great purity by 

 known methods, it was found very difficult to obtain fused solutions free 

 from a slight precipitate of reduced silver. Hence, in order to avoid 

 danger of error from this source, the fused mixture was filtered by its 

 own gravity through an asbestos mat in a Gooch crucible, the whole 

 apparatus being heated to 250° in a clean air-bath. Thus may be 

 obtained a limpid and colorless fused mixture, which was used imme- 



* Richards and Heimrod, loc. cit. 



