J4 NEW METHOD FOR DETERMINING COMPRESSIBILITY 



Constancy in the readings was reached in five minutes. The glass 

 jacket in this case contained a bulb of chloroform immersed in the 

 mercury. 



The quantity of mercury in the glass jacket was usually so adjusted 

 that the first constant pressure reading was between fifty and one hun- 

 dred atmospheres, and this first reading was taken as the starting point 

 of the determination. Minute air bubbles were thus disarmed of pos- 

 sible injurious effect. As already suggested, a weighed quantity of 

 mercury was now added through the funnel tube (see Fig. 2) and 

 pressure again applied. The added pressure necessary to break the 

 electrical circuit corresponded to the volume of the extra mercury in- 

 troduced. This process was repeated until the highest pressure was 

 reached, and thus were found the points on a curve which depicts the 

 difference between the compressibilities of mercury and glass. Only 

 in the most accurate work is it necessary to consider the compression 

 of the small extra volumes of mercury introduced, since the omission 

 of this correction causes an error of only 0.04 of one per cent, for every 

 hundred atmospheres. 



If now there is introduced beneath the mercury the substance whose 

 compressibility is to be determined, and a new curve is found in the 

 same way, it is evident that the differences between these two curves 

 represent the differences between the compressibility of the new sub- 

 stance and an equal volume of mercury. 



A tvpical series may better serve to make clear the method of obser- 

 vation and calculation. The first process is the calibration of the glass 

 jacket with mercury already described. The pressure readings given 

 below were taken after successive additions of mercury, the whole 

 apparatus being filled with this liquid. 



Initial reading: Circuit made 37, 37, 37, 37, 37 kg. /cm 2 . Circuit 

 broken, 40, 39, 39, 39, 39 kg/ cm 2 . 



After adding first quantity of mercury, =0.1020 gram. Circuit 

 made 254, 255, 254, 254, 254 kg./cm 2 . Circuit broken 257, 256, 

 256, 256, 256 kg./cm 2 . 



After adding second quantity of mercury, = 0.0998 gram. Circuit 

 made 476, 476, 476, 476 kg./cm 2 . Circuit broken 47S, 478, 478, 

 478 kg./cm 2 . 



After adding third quantity of mercury, = 0.0660 gram. Circuit 

 made 632, 634, 634, 634, 634 kg./cm 1 . Circuit broken 636, 636, 636, 

 636, 636 kg./cm 2 . 



A bulb filled with bromine was now put into the jacket ; the remain- 

 ing space was filled with mercury and a new series of pressure 



