APPARATUS I 



3 



readings taken. The weight of the bromine was 7.502 grams, while 

 the thin containing bulb weighed only 0.72 gram. 



Initial reading: Circuit made 68, 68, 68, 68, 68 kg. /cm 2 . Circuit 

 broken 70, 70, 70, 71, 69 kg. /cm 2 . 



After adding first quantity of mercury, = 0.3338 gram. Circuit 

 made 223, 223, 223, 223 kg. /cm 3 . Circuit broken 227, 225, 225, 225 

 kg. /cm 2 . 



After adding second quantity of mercury, =0.3357 gram. Circuit 

 made 391, 392, 392, 392, 392 kg./cm 2 . Circuit broken 393, 394, 

 393' 393 kg./cm 2 . 



After adding third quantity of mercury, = 0.3259 gram. Circuit 

 made 566, 565, 565, 565, 565, 565 kg./cm 2 . Circuit broken 567, 



5 6 7> 5 6 9> 5 6 7> 5 68 > 5 6 7 kg./cm 2 . 



From the results with mercury a curve is plotted with pressures as 

 abscissas and total weights of mercury as ordinates. The ordinates on 

 this curve which correspond to the pressures found in the series with 

 bromine evidently represent the weights of mercury which are to be 

 subtracted from the weights actually added in the bromine series in 

 order to obtain a basis for calculating the difference between the 

 volume change of the bromine and the change in an equal volume of 

 mercury. 



The equation for calculating the average compressibility between 

 the pressures P x and P 3 , i. e., the volume change for a unit of the 

 original volume subjected to an increase of a unit of pressure, is 

 obviously : 



WP&5 + ' 



where 



, /9', and /3" equal respectively the average compressibilities of the 



substance studied, mercury, and glass ; 

 iv and iv' equal respectively the two weights of mercury in the two 



series above described corresponding to the given change of 



pressure P 1 P t . 

 w" and ^respectively the weights of the thin glass bulb and the 



substance studied ; 

 d and D the densities of glass and of this substance, and, 

 13.546 the density of mercury at 20 . 

 The value /3' /3" is obtained, as will be seen later, directly in the 



