504 Johnston and Adams — Influence of Pressure on the 



The electric furnace, depicted at JJ, and the arrangement 

 of the interior of the bomb, will be described later on. 



The pressure in the system may be raised by means of the 

 pump t> (fig. 1). It has a plunger 8 mm in diameter, and is of 

 the type ordinarily used with hydraulic presses. With this 

 pump we have obtained without difficulty pressures up to 2000 

 atmospheres. It communicates through the pipe with the 

 oil-supply tank (not shown in the diagram) and forces oil out 

 through the steel bottle F and the connection block C into the 

 bomb. The bottle F, which has a capacity of about one liter, 

 serves to increase the volume of the system, which otherwise 

 would be less than 100 ce , and thus makes for greater constancy 

 of pressure during heating and cooling and during changes 

 such as occur when the material under investigation melts or 

 solidifies. 



The connection block C affords a 4 way connection between 

 the pump, the bomb, the gage, and the release valve V. The 

 gage M, of the Bourdon type, is a new one manufactured by 

 Schaeffer and Budenberg, and was calibrated by them. It is 8 

 in. in diameter and is graduated up to 3000 atmospheres in 

 divisions of 50. The indications of Bourdon gages, as is well 

 known, are subject to a hysteresis effect ; that is, the reading 

 corresponding to a certain pressure may vary slightly, depend- 

 ing on whether the pressure is rising or falling. From various 

 considerations, however, the writers are led to believe that the 

 discrepancy in the present instance is small and that the readings 

 of the gage are subject to a probable error no greater than ± 5 

 atmospheres, — an accuracy quite sufficient for the present 

 purpose.* 



The valve V serves to lower the pressure in the system or 

 to release it entirely ; it is shown in greater detail in fig. 2, 

 which is drawn exactly to scale. The valve-stem, which 

 ends in a cone fitting into a conical depression in the valve 

 block, is kept in place by the nut m. The packing consists of 

 three layers of leather surmounted by a steel disk. The pitch 

 of the screw between stem and nut is identical with that 

 between nut and block ; by this means the valve is not jammed 

 down into its seat, when the nut m is tightened. 



Fig. 2 serves also to illustrate the type of high pressure 

 connection which has proved uniformly satisfactory for mak- 

 ing all the connections necessary in work, such as the present, 

 where high pressures are employed. On account of its sim- 



* We have under construction an absolute gage, of the piston type 

 described by P. W. Bridgman (Proc. Am. Acad., xliv, 119-251, 1909), by 

 means of which we shall be able to measure pressures with an accuracy of - l 

 per cent. In the present work its use was unnecessary by reason of the 

 comparatively small influence of pressure on the melting points which we 

 have investigated. 



