292 SCIENCE PROGRESS. 



partly of copper be immersed in a solution, the observed E. 

 M. F. is that between copper and zinc. If the zinc in the 

 composite plate were finely divided and mixed with the 

 copper it may be assumed that the result would be the 

 same. If, however, the zinc combined with the copper, 

 the E. M. F. would be that between the compound and 

 copper. Consequently, if we keep on adding zinc to the 

 copper, and a compound is formed, a point will eventually be 

 reached at which the copper is saturated, and free zinc will 

 then be present in the plate. When this happens there will 

 be an abrupt rise in the E. M. F., for it will now be that 

 between copper and zinc, and the composition corresponding 

 with the rise will be that of the compound of copper and 

 zinc. In this way the author has previously inferred that 

 Cu Zn 2 and Cu 3 Sn exist, and he now finds (80) that his 

 observations lead to the same results as measurements of 

 electrical resistance in the case of the alloys examined by 

 Mathiessen. Using alloys of the metal-pairs, Bi-Sn, 

 Bi-Pb, Bi-Zn, Bi-Au, Bi-Ag ; Au-Ag, Cd-Zn, 

 Sb-Sn, and Sb-Pb, in the last case alone was there 

 evidence of combination. Ostwald (81) has pointed out 

 that these observations would be more valuable if more 

 attention had been paid to the composition of the solutions in 

 which the alloys were immersed, because the E. M. F. de- 

 pends on the concentration in the solution of the ion of the 

 metal plate, and from the mode in which the experiments 

 were made different amounts of metal might have dissolved 

 in the solutions in different cases. 



According to Haas (82), the copper-zinc alloy, which 

 has the maximum specific resistance, has the composition 

 expressed by Cu 2 Zn. Since alloys containing from 47 to 

 99 per cent, of copper could not be drawn into wire, the 

 author was unable to test by this method the existence of 

 Laurie's Cu Zn 3 alloy. It is to be hoped that efforts will 

 soon be made to see whether these different methods lead 

 to the same results, for in the present state of the theory of 

 solids such agreement would constitute the strongest proof 

 of their validity. 



Wiesengrund (83) has tried to show that the lead-tin 



