OF ZINC, CADMIUM, LEAD, COPPER, AND LITHIUM 65 



the cell in the present calculation involved much further dilution than 

 that corresponding- to the thermochemical experiment. In the present 

 case one amalgam was about nine times as dilute as the other, while in the 

 thermochemical experiment the dilution was only to double the bulk. 

 Nevertheless, even allowing for the heat which would be absorbed by the 

 further dilution of the amalgams, it is clear that the electrochemical 

 estimate of the cooling effect exceeds the actual thermochemical measure- 

 ment. This lack of coincidence was to have been expected from the 

 results already chronicled in the preceding section of the monograph, 

 concerning thallium, indium, and tin ; in each of these cases also the ther- 

 mochemical effect appeared to be too small, and in the case of lead, soon 

 to be discussed, the same discrepancy was observed. The lack of agree- 

 ment is undoubtedly due not to fault in the Helmholtz equation, but 

 rather to the inadequacy of the clockwork stirrer used in the thermo- 

 chemical work. Liquid amalgams, because of their great inertia, are hard 

 to mix ; but their ready conductivity quickly establishes a nearly equable 

 temperature throughout, even when they are not thoroughly mixed. 

 Hence it is easy to be deceived concerning the results. 



In spite of the lack of exact agreement, the thermochemical result of 

 Richards and Forbes is nevertheless of value, for it shows that liquid zinc 

 amalgams really produce a large cooling effect upon dilution, and it thus 

 confirms, both as to sign and as to order of magnitude, the results of the 

 electrical measurements. 



Turning to cadmium we find that the work of Richards and Forbes has 

 quantitative as well as qualitative significance. By reference to the origi- 



nal data, 67 it is seen that at o TT:= 30.826 millivolts and ~ =0.003655, 



therefore 



, ---- 5951 joules 



ATT 



vFT 'Kr ................................... 59S7 J oules 



U .................................. = 6 joules 



This difference is no larger than the possible error of experiment, and its 

 sign is therefore somewhat uncertain ; but nevertheless it is supported by 

 the very small cooling effect which was at that time actually found. In 

 this case, the inadequacy of the mixing in the thermochemical experiment 

 would have very little significance, because the effect to be observed 

 formed so trifling a part of the whole phenomenon. 



In this connection it may be noted that Carhart M assumes on the basis 

 of his theory, without any published experimental justification, that the 



"Carnegie Institution of Washington, Publication No. 56, pp. 50 and 57 (1906). 

 68 Phys. Rev., 26, p. 216 (1908). 



