APPARATUS 



17 



The greater part of the mercury was now withdrawn, and the resi- 

 due, filling the U-tuhe at least, was weighed with the glass. Subse- 

 quently the liquid under investigation was drawn 

 in, completely displacing the air; and finally the 

 apparatus, after external drying, was weighed 

 again. Thus was found the weight of the liquid 

 to be compressed. 



The jacket was now placed once more in the 

 Cailletet barrel, and once more the pressures cor- 

 responding to successive added portions of mercury 

 were found. These new readings define the curve 

 of compressibility of the liquid and the residual 

 mercury. The differences between the weights of 

 mercury added, for any given change of pressure, 

 as found on the two curves, give by simple calcu- 

 lation the differences between the compression of 

 the given volume of liquid and the same volume 

 of mercury, hence the compressibility is easily 

 computed with the help of the following equation, 

 in which the symbols have the same significance 

 as before. 



/* 



13.546 ^(/^-y.) 



+ /?' 



(3) 



Compressibility of Mercury and Glass. 



Since both the difference between the compres- 

 sibility of glass and mercury and the absolute com- 

 pressibility of mercury enter into the equations, 

 it is important at the outset to determine these 

 quantities as definitely as possible. Accordingly 

 several careful series of experiments were made. 

 Because the change in the capacity of a hollow 

 glass vessel under compression is equal to the 

 change in the same volume of solid glass, the value 

 yS' ft" may be determined by compressing mer- 

 cury in the jacket already described. Three of 

 these jackets, numbered I, II and III, were of the 

 type suitable for solids depicted in Fig. 2, while 

 the fourth was of the type designed for liquids, 

 depicted in Fig. 3. In the table below the actual 

 figures found with these four jackets are given, and in the third 

 column the added weights of mercury tv f are all divided by the total 



Fig. 3. 



