34 THE COMPRESSIBILITY OF CARBON, SILICON, 



THE DETERMINATIONS OF COMPRESSIBILITY. 



All the preliminary data having thus been found, the solid to be studied 

 was placed into the jacket thus prepared and tested. The operation was 

 usually conducted and the weight of the water was usually found in the 

 following way: The jacket containing a little mercury, its stopper already 

 lubricated with a weighed amount of lubricant, the solid to be studied, 

 and a bottle containing an excess of pure mercury were all placed upon 

 the balance-pan together, and weighed to within a milligram. The solid 

 was then placed within the jacket, water or oil was added (after exhaust- 

 ing the air if necessary), and mercury was carefully supplied from the 

 bottle in sufficient quantity. After closing the jacket and cleaning it 

 externally, it was once more weighed with the bottle and residual mer- 

 cury. The gain in weight of the total load was the weight of the water 

 or oil in the jacket. 



When operating with powders not attacking mercury, the following 

 method may be used with advantage. The jacket with a small amount of 

 mercury in it, together with an additional tube of mercury, a little plati- 

 num disk, and the lubricated stopper were weighed all together. The 

 powder under investigation was then placed into the jacket and packed 

 down with a glass rod. On the top of this powder was placed the plati- 

 num disk, which was firmly wedged so as to prevent the powder from 

 being thrown out during the subsequent treatment. The apparatus was 

 reweighed to obtain the weight of the powder. The jacket (unstoppered) 

 was then placed into the apparatus shown in fig. 6, in which apparatus 

 A was filled with dry ether, while B was filled with the supplementary 

 liquid (either water or oil of known compressibility) to be used to transmit 

 the pressure to the powder. The apparatus was then evacuated and D 

 closed, and ether vapor was boiled back into the apparatus from A. After 

 closing C the whole was evacuated again ; and the process was repeated 

 again and again, alternately exhausting and filling with ether vapor four 

 times. The object of this treatment was to displace every trace of air in 

 the interstices with ether vapor, which would quickly be reduced to 

 vanishingly small proportions under pressure. The vessel was finally 

 exhausted to 2 or 3 mm. pressure and the liquid was allowed to run down 

 from B. Air was now slowly admitted, always keeping a layer of liquid 

 above the powder. In this way all the empty space was filled by the oil 

 or water. The apparatus was now taken out and a plug was tied down 

 upon the top of the platinum disk. Mercury was poured into the long 

 narrow arm of the jacket and pressure from a common bicycle pump was 



