IO NEW METHOD FOR DETERMINING COMPRESSIBILITY 



had no knowledge of the change of solubility of bromine in water 

 with change of pressure. Moreover, the bromine in the vicinity of 

 water must have been saturated with the latter substance ; hence 

 the result was at best an approximation. When the bulb was in the 

 upper receptacle, the force of gravity assisted the adhesion of the bro- 

 mine to the walls of the tube, and the adhering bromine was clearly 

 visible ; but when the bulb was below, gravity had the contrary effect, 

 and the adhesion became less serious. 



In the first position, a pressure of 50 kilograms per square centi- 

 meter was found in one tube to cause an apparent compression of 

 0.284 P er cent - or tne volume of the bromine and 0.007 P er cent - or the 

 volume of the mercury. Thus the difference between the compressi- 

 bility of mercury and bromine was found to be 0.0000554, the unit of 

 pressure being taken as a kilogram per square centimeter. Adding to 

 this the compressibility of mercury, 0.00000380, the value 0.0000592 

 is obtained for that of bromine, a value probably too high for the 

 reasons already named. 



Other trials, with a wider tube and with the bulb in the lower envel- 

 ope, diminished the error due to the adhesion of bromine. Thus the 

 percentage change of volume for pressures of 50, 100, and 150 kilo- 

 grams per square centimeter respectively were found to be 0.272, 

 0.538 and 0.797 per cent, for bromine, and 0.011,0.022 and 0.033 

 per cent, for mercury respectively. These data lead to the following 

 values of the compressibility of bromine from o to 50 atmospheres, 

 0.00005S2 ; from 50 to 100 atmospheres, 0.0000576 ; and from 100 to 

 150 atmospheres, 0.0000570. The temperature was 17 C. As will 

 be seen later, these values are not far from the true ones ; and they are 

 consistent enough to show a steady decrease of compressibility with 

 increasing pressure, which seems to be the universal rule. 



The experience thus gained led to the devising of a new method re- 

 taining all the advantages, and at the same time obviating all the dis- 

 advantages of the previous procedure. In this new method, the bro- 

 mine, instead of being in contact with any other fluid, was enclosed 

 hermetically in a very thin, flat flexible glass bulb, containing no other 

 substance. The decrease of volume in this bulb upon compression was 

 determined as if it were a homogeneous solid, by compressing it 

 under mercury in a suitable vessel to be described later. Allowance 

 is easily made for the change in volume of the mercury and glass, if 

 the containing apparatus has been properly tested full of mercury in 

 the first place. 



Since the bulbs were so thin as to collapse under a pressure of less 



