HOLMAN, LAWRENCE, BARR. — MELTING POINTS. 219 



Hunt, President of the company, to contain but 0.07 per cent of 

 impurity, consisting entirely, of" silicon. 



The platinum was the ordinary platinum wire supplied by Carpen- 

 tier 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.D9+ 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 were : — 



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

 chased as being of good quality. 



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

 Smelting Company, who gave its analysis as 



Cu 99.825 



Ag . 0.032 



As 0.003 



S 0.022 



Fe 0.003 



O 0.116 



100.001 



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



Oommercial Electrolytic Copper. — A sample of commercial elec- 

 trolytic 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 ohms per meter-gram, or an elec- 

 trical conductivity of about 98.3 per cent referred to Matthiessen's 

 copper. 



Methods and Apparatus. — The method consists in measuring the 

 thermal electro-motive force of a couple composed of one wire of 

 platinum and the other of a 10 per cent rhodo-platinum alloy. One 

 junction is immersed in the melting or solidifying metal, and the other 

 surrounded by ice. The wire was that furnished by Carpentier of 



