ON THERMO-ELECTRIC HETEROGENEITY IN CER- 

 TAIN ALLOYS, ESPECIALLY GERMAN-SILVER. 



By Edwin H. Hall, L. L. Campbell, and S. B. Serviss. 



Presented December 13, 1905. Received January 2, 1906. 



Purpose and General Plan op the Investigation. 



In a paper on " Thermal and Electrical Effects in Soft Iron," published 

 in these Proceedings for May, 1905, by the authors of the present paper, 

 together with Mr. E. P. Churchill, brief account was given, at pages 

 42-45 and 54, of the construction and calibration of two sets of copper 

 and german-silver thermo-electric couples, which will hereafter be 

 referred to as A, B, C, D and A lf B l5 Ci, D x , respectively. The study 

 of these couples, all of which were made from one original piece of 

 copper and one original piece of german-silver, was confined to the tem- 

 perature range 0° C. to 100° C, as the experiments on soft iron, to 

 which experiments the thermo-electric couples were contributory, lay 

 within this range. 



It was intimated, however, in the paper already mentioned, that 

 similar experiments on iron through the interval from 100° C. to 200° C. 

 would presently be undertaken, and with a view to this work a study 

 of copper and german-silver thermo-electric couples through this higher 

 range became necessary. It was hoped, too, that these proposed calibra- 

 tion tests could be carried out with such accuracy and thoroughness as to 

 add something valuable to our knowledge of the general behavior of 

 such thermo-electric couples, the permanence or variability of quality 

 in any particular couple, for example, or the causes and magnitude of 

 the differences between couples made, as nearly as may be, of the same 

 materials and in the same way. These secondary purposes of the inves- 

 tigation have been in some measure fulfilled, through variations of 

 experimental conditions which were not at first planned and which seem 

 to us worthy of being described with some detail. 



More strictly, the higher limit of temperature now proposed was the 

 boiling point of naphthalin under atmospheric pressure, about 218° C. 



