10 



THE COMPRESSIBILITY OF LITHIUM, SODIUM, 



room itself in which the whole apparatus was placed was kept constant in 

 temperature by a gas-barometric electrical thermostat, at about half a 

 degree below the temperature of the water of the vessel. The regulation 

 of the temperature of the room, of course, assisted materially in promoting 

 the constancy of the bath. The thermometer used was carefully compared 

 with the international standard and all determinations of compressibility 

 were made at exactly 20.00 of the international hydrogen scale. 



Two types of glass tube were used to contain the alkali metals to be 

 compressed. Because these metals could not be allowed to come into con- 

 tact with mercury, the forms used in the previous work were inapplicable ; 

 but slight modifications removed the objections. The two forms used are 

 shown in the accompanying diagram, the form A (fig. 2) having been 

 used in the preliminary work, and the much more satisfactory and con- 

 venient form V (fig. 2) having been used in the final determinations. 

 These were constructed of carefully annealed glass and provided with very 

 finely ground stoppers. 



Fig. 1 . The Compression Apparatus. 



It will be remembered that the tube or glass jacket was at first filled com- 

 pletely with mercury, and the change in volume for different pressures was 

 measured very simply by placing the whole jacket under the liquid in the 

 barrel of the Cailletet compression apparatus, adding successive weighed 

 portions of mercury, and noting each time the pressure needed just to 

 break and then again make the electrical connection between the meniscus 

 and the platinum point (P). The quantity of mercury in the glass jacket 

 was usually so adjusted that the first constant pressure reading was between 



