95 



Note on the Determination of A''apor Densities. 



By Chas. T. Knipp 



The object of this note is to describe briefly a method of determining 

 vapor densities which was suggested to the writer last year while maliing 

 observations on the surface tension of water at high temperatures. 



The principle used is that the buoyancy of vapor increases as the 

 density increases. An iron core mn (Fig. I), carrying a sphere S at its 

 lower end is lifted by the sucking action of a coil in whicli a current 

 is flowing. The lifting coil and core with sphere attached are contained 

 in a steel vessel of suflacient strength to withstand high pressures. Three 

 insulated circuits are run through the plug closing the vessel. The scheme 



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of connections is shown in Fig. I. The lifting current is supplied by a 

 number of storage cells, the current being adjusted by tin resistances 

 until the sphere is lifted. At that instant contact is made at M, closing 

 the signal circuit, shown to the right in the figure. The temperature is 

 read by means of a Cu-Pt thermo-junction. This is placed in a hole 

 drilled in the containing vessel to within 2mm of the inner cavity. The 

 vessel communicates with a pressure gauge and pump. The current re- 

 quired to lift the sphere is read by means of p milli-volt meter looped 

 aroimd a .03-ohm coil. 



