High Temperatures. 



195 



ifying points. This seems to indicate that the copper under 

 these conditions becomes saturated with a definite quantity of 

 oxygen or rather with a copper oxide. 



To assure ourselves regarding the constancy of this point we 

 have made a great many observations of it without being able 

 to notice any essential variation. 



It was also quite indifferent whether the copper was fresh 

 or had been several times used for the same purpose before. 



After many determinations with a particular mass of metal 

 it seemed to melt with increasing difficulty, a phenomenon 

 which points to a decrease in its conductivity for heat, but 

 should receive rather more investigation. Table XIX con- 

 tains the results of the observations, giving 1064'9° as the melt- 

 ing point of copper in air. 



(2) In a Reducing Atmosphere. — If the same metal which 

 has been repeatedly melted in air be heated in a plumbago 

 crucible it gradually reduces and the melting point rises, ulti- 

 mately reaching 1084° after the metal has remained for a long- 

 time in a molten condition and become thoroughly reduced. 



Melting points obtained between 1065° and 1084° where 

 the reduction is 'still incomplete give poorly defined curves. 



At the close of Table XIX some observations with the pure 

 metal are given. Fig. 5 shows time curves for observations in 



Minutes 



porcelain crucibles (curves A and B) as well as in graphite 

 (curves C and D). 



If the melted copper contained oxygen, the unglazed por- 

 celain tube which served to protect the thermo-element was 



