Johnston and Adams — Melting Points of Metals. 501 



Art. XLI1. — The Influence of Pressure on the Melting 

 Points of Certain Metals ; by John Johnston and L. H. 

 Adams. 



The authors have been engaged in developing methods and 

 apparatus by means of which it will be possible to investigate the 

 effect of high temperatures and pressures on certain systems and 

 reactions, and especially those in which water plays an impor- 

 tant part. The work has progressed until now we are able to 

 introduce into the bomb current leads and thermoelement 

 wires in such a manner that the wires are all thoroughly insu- 

 lated electrically, and the joint remains absolutely pressure 

 tight. Thus, it is possible to heat a substance to somewhat 

 over 400°,* under pressures up to 2000 atmospheres ;f and to 

 measure both temperature and pressure with precision. More- 

 over, the whole system, by reason of the special methods of 

 construction adopted, is absolutely free from pressure leaks, 

 even when the bomb is repeatedly closed and opened, discon- 

 nected from, and reconnected with, the remainder of the high 

 pressure system. For instance, on one occasion heating was 

 continued for 30 hours continuously at a pressure of 1800 

 atmospheres, without sensible loss of pressure in the whole 

 interval. 



Before proceeding further in the main purpose of the work, 

 it seemed desirable to make a rigorous test of the precision of 

 temperature measurements under these conditions. For this 

 purpose, determinations of metal melting points are suitable 

 by reason of their definiteness. Accordingly it was resolved 

 to investigate the effect of pressure upon the melting point of 

 tin, bismuth, lead and cadmium, the four metals which lie 

 within our present range of temperature. The results are 

 eminently satisfactory, for, as we shall see, a precision in the 

 temperature measurements of about # 02° was reached, using 

 a thermocouple of copper-con stan tan, for which an electro- 

 motive force of one microvolt corresponds to about - 02°. It 

 may here be said that the results of this investigation are in 

 entire accord with what was to be expected from the magnitude 

 and direction of the heat change and volume change which 

 accompany the process ot melting ; and that the small discrep- 

 ancies between the observed and the calculated values are to be 

 ascribed mainly or entirely to uncertainty in the experimental 

 determinations of the latent heat of fusion and of the change 

 of density on melting. 



* The highest temperature the oil will stand without serious charring, 

 f The limit of the present compression pump. 



Am. Jour. Sci. —Fourth Series. Vol. XXXI, No. 186.— June, 1911. 

 34 



