230 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



TABLE II. 



The concordance of these results on various coppers, together with 

 the completely satisfactory behavior of the metal in fusion, and the 

 ease and cheapness of obtaining the metal of a very high grade of 

 fineness, suggest the decided availability of copper in a direct study of 

 high temperatures or melting points by the gas thermometer. A 

 large mass of the metal could be employed, and a constant and uni- 

 form temperature for a protracted period thus secured for the bulb of 

 the gas thermometer, or for other apparatus immersed in the molten 

 or solidifying material. There are unfortunately too few substances 

 which fulfil even these requirements. An added merit lies in the 

 nearness to the gold melting point, enabling the two to be satisfactorily 

 connected by some means of relative measurement. 



It also appears that the use of good commercial copper would 

 introduce sensibly less error (3° less) into the calibration of the 

 Le Chatelier pyrometer than the use of the '' dentists' gold " above 

 tested, which is as good metal as would readily be obtained in the 

 market by most observers. 



ReHability of the Results. —The points involved are : — 



Instrumental errors. 



Purity of the metal. 



Was the observed point the real melting point? 



Validity of the interpolation equation. 



Error in the assumed melting point of gold and boiling point of 

 sulphur. 



The investigation was planned and the apparatus arranged with the 

 intention of reducing the combined instrumental errors below one 



