Melting Points of Certain Metals. 



511 



curves.* The uncertainty in the temperatures deduced in this 

 way from the above table should, we believe, not exceed 01° 

 on the temperature scale we have chosen ; and is much smaller 

 than the present uncertainty in the absolute value of the 

 temperature scale — an uncertainty which is about 1° at 450°. 

 The readings may be immediately referred to any other scale 

 of temperature by including in the deviation curve the differ- 

 ences between the two scales. Temperature differences, how- 

 ever, over a small range are probably accurate at least to , 02°, 

 regardless of slight discrepancies in the temperature scale, and 

 of possible errors in the interpolation formula. For this reason 

 the values of temperatures and differences in Table I are given 

 to hundredths of degrees. 



Melting Point Determination. 



Briefly, the method pursued in the determination of the 

 melting points of the various metals under pressure was as 

 follows : A charge of the proper amount of metal having been 

 placed in the graphite crucible, the whole was heated some- 

 what above the melting point of the metal (a thin layer of oil on 

 the surface of the metal prevented oxidation). The porcelain 

 tube which serves to protect the thermocouple from the sur- 

 rounding metal, attached to the crucible lid, was fitted into 

 position. Crucible, steel plug (G, fig. 3), soapstone cylinder, 

 etc., were then assembled and placed in the bomb, which was 

 thereupon set in position on the lower platen of the press, and 

 connected with the high pressure line (at _£ 7 , fig. 1). The 

 upper press platen was forced down until the upper plug (G) 

 slipped into place and centered itself ; the electrical connections 

 were made, the cooling waterf turned on, and all was in readi- 

 ness for the actual measurements. 



The pressure inside the bomb was increased by means of the 

 pump J), while simultaneously excess pressure in gradually 

 increasing amount,;]: was applied by means of the press, on the 

 plugs G and H. When the desired pressure was attained, the 

 freezing point of the metal was determined as usual by the 

 Frankenheim method. 



No account was taken of the effect of pressure on the 

 thermoelectric E.M.F. This influence is very slight in those 



* This matter is more fully treated in Sosman, loc. cit., q. v. 



f A supply of both hot and cold water was available ; for most of our 

 experiments hot water was used to "cool" the bomb. By the use of hot 

 water in this connection a smaller heating current is required; in addition, 

 this plan makes for more uniform temperature distribution within the 

 bomb. 



tWhen the pressure was decreased again by releasing the valve V, a 

 corresponding diminution in the external pressure exerted by the press 

 was effected by suitable manipulation of the proper valves. 



