502 Johnston and Adams —Influence of Pressure on the 



Briefly, the method pursued in this investigation is as fol- 

 lows : A charge of the metal to he investigated was placed in 

 a suitable apparatus for heating it under pressure ; its freezing 

 point or melting point was then determined, at constant 

 pressure, using the Frankenheim method. A small electric 

 resistance furnace supplied the heat ; a thermocouple was used 

 to measure the temperature of the metal ; and a high boiling 

 paraffin oil served to transmit the pressure. 



Description of the Apparatus. 



The essential parts of the apparatus are : the bomb, in which 

 the substance to be heated under pressure is placed ; the pump, 

 with which to supply the pressure ; and a gage for measuring 

 it. In fig. 1 is shown the arrangement of these parts, together 

 with the accessory apparatus consisting of valves, pressure- 

 line connections, oil-reservoir, thermocouple, heating current 

 wires, etc. In this diagram the bomb is drawn to scale but the 

 remainder of the apparatus only approximately so. The bomb 

 itself (the interior of which is shown in greater detail in fig. 3) 

 was built up of a cylinder of machine steel KK, on to which 

 were shrunk a ring of nickel steel PR and a number of thin- 

 ner rings of boiler-plate separated from one another by a space 

 of about 4 ram . Water enters at W x , circulates between the rings 

 and around the central cylinder KK, and leaves at W t * The 

 bomb is closed by means of two hardened steel plugs, G and 

 H, held in place by a 500 ton hydraulic press, the platens 

 of which are shown at PP. On the shoulder (LL, fig. 3), 

 of either plug is turned a Y-shaped ridge, and on the adjacent 

 shoulder of the bomb a groove to correspond. Between the 

 groove and ridge lies a ring or " washer " of thick sheet cop- 

 per ; by maintaining with the press a force of about 20 tons in 

 excess of that exerted on the inside surface of the plug by the 

 internal pressure, the bomb is effectively and easily closed. 

 Opening the bomb again — after it has been removed from the 

 press — is effected with the aid of a large nut which fits the 

 heavy screw thread cut on G. 



Experience has shown that without some device for center- 

 ing the bomb and plugs with respect to the press platens, 

 good and certain closure of the bomb is not possible, time 

 after time. The arrangement used for this purpose is worthy 

 of mention ; it is very simple and consists merely of the curved 

 surfaces of A and G on the one end, and of A and B on the 

 other. By this arrangement practically perfect alignment is 



*This water-cooling device leaves nothing to be desired as regards effi- 

 ciency, but is somewhat difficult to construct and to make water-tight. It is 

 not of our own design, the bomb having been reconstructed from one which 

 had been designed and built by Dr. A. Ludwig, 



