44 



ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



In like manner the value of the ordinate (log ^2. 1.48787) is fixed as 



0.00164, and the curve extended to the still greater dilution of amalgams 

 15 and 16, made from amalgam 9. 



On plotting these values (figure 7), the improvement due to the rigid 

 exclusion of oxidation is manifest. 



The close approach of the " oxidation curve " to the true curve in the 

 region of point 2 shows that amalgam No. 2 was not measurably affected 

 by oxidation ; this effect became manifest only with very dilute amalgams ; 

 it was obviously due to the oxygen absorbed during some part of the compli- 

 cated manipulation involved in the earlier experiments. 



Lack of time prevented the investigation of the extremely dilute amalgams 

 beyond points 15 and 16. It seems safe to conclude, however, that the 

 observed potentials will continue to approach their calculated values still 

 more closely as the dilution is increased, for the curve is evidently becoming 

 more and more nearly horizontal as the dilution proceeds that is to say, 

 is approaching more and more nearly to the requirements of the gas law. 

 It is to be noted that even amalgams 15 and 16 are very dilute, containing 

 only about 0.014 per cent of zinc by weight. This matter will be discussed 

 further when the results with cadmium have been given. 



In concluding this portion of the work, it is worth while to point out that 

 the success of the measurements depended wholly upon the chemical side 

 of the investigation, namely, upon the purification of the materials, and 

 especially upon the rigorous exclusion of oxidation. The physical measure- 

 ments of course demanded great care, but they involved nothing new. On 

 the other hand, the effect of the few hundredths of a milligram of oxygen 

 would have wholly vitiated the results if this oxygen had not been wholly 

 excluded ; and the detection and elimination of this cause of error caused 

 the chief labor of the research and determines its value. 



INFLUENCE OF THE CONCENTRATION OF THE ELECTROLYTE. 



The electrolyte used in the original measurement of Nos. 1-22 was 

 analyzed by titration with ferrocyanide solution. Its concentration was very 

 nearly one-tenth molal. A new electrolyte was made up from chemically 

 pure zinc sulphate, ten times as strong as the above, and this was freed 



