38 Messrs. Holinan, Lawrence, and Barr on the 



The silver was from the same source and equally pure. 



The aluminium was manufactured and given by the Pitts- 

 burg Reduction Company, of Pittsburg, Penn., and was stated 

 by Sir. Alfred E. Hunt, President of the Company, to con- 

 tain but O07 per cent, of impurity, consisting entirely of 

 silicon. 



The platinum was the ordinary platinum wire supplied by 

 Carpentier, of Paris, with his Le Chatelier thermo-electric 

 pyrometers. It presumably contained 0*5 per cent, or more 

 of impurity. 



The copper was electrolytically produced, and was from 

 the Lake Superior region. It was kindly given by Mr. 

 Maurice B. Patch, of the Buffalo Smelting Company, Buffalo, 

 N.Y., who stated that it showed by analysis 99*99 + per cent, 

 of Cu, and contained no Ag, As, or S, and only 0'0002 per 

 cent, of Fe. 



The Less Pure Metals. — Partly for the purpose of testing 



the effect of impurities, other samples of gold and copper 



were employed with the results stated later. These w r ere : — 



Dentists' Gold. — This was a gold-foil employed by dentists, 



purchased as being of good quality. 



Ingot Copper. — -This was also from Mr. Patch, of the Buffalo 

 Smelting Company, w r ho gave its analysis as : — 



Cu 99-825 



Ag 0-032 



As 0-003 



S 0-022 



Fe 0-003 



O 0-116 



100001 

 This was the company's " regular run ' J of copper. 



Commercial Electrolytic Copper. — A sample of commercial 

 electrolytic rolled sheet copper, furnished by a friend, and not 

 assumed to be of unusual purity. It was probably Montana 

 copper. 



Commercial Hard-drawn Copper Wire. — This was from a 

 lot purchased for electrical testing purposes, which showed a 

 specific resistance of 0*1440 international ohm per metre- 

 gram, or an electrical conductivity of about 98'3 per cent, 

 referred to Matthiessen's copper. 



Methods and Apparatus. — The method consists in measuring 

 the thermal electromotive force of a couple composed of one 

 w T ire of platinum and the other of a '- iO-per-cent. rhodo- 

 platinum alloy. One junction is immersed in the melting or 



