PHOSPHORUS 



37 



superposed in the usual manner, give very consistent values. The 

 averages are given below, together with the compressibility of phos- 

 phorus computed from them, for each ioo units of pressure. The 

 quantity A B represents the value in the large brackets of equation 

 (5), from which /9 /?' is easily calculated. 



Compressibility of Phosphorus. 



Thus the compressibility of phosphorus is about half that of water 

 and more than five times that of mercury. 



Water. 



Four reasons make it desirable to determine the compressibility of 

 water. In the first place, this liquid could be accurately used in both 

 forms of apparatus, and hence could serve as a certain means of com- 

 paring the results of each. Again, so many investigators have de- 

 termined this quantity that it serves as an excellent means of comparing 

 our method with those of others. Further, the value obtained by our 

 present apparatus may at some future time, by comparison with the 

 results of an experimenter with a perfect pressure gauge, serve con- 

 veniently to determine by backward calculation the error of our pres- 

 sure-gauge, and thus correct all the results in this paper. Finally, the 

 compressibility of water at pressures above 262 atmospheres seems 

 never to have been determined. 



The water used in the determinations described below was purified 

 by two successive distillations, the first one being from permanganate 

 solution. It was boiled just before being used, to expel the air. 



As has been stated, its compressibility was determined in two ways, 

 first, by the method used with the bromine ; and second, by the 

 method first used with bromoform, namely by means of the jacket de- 

 vised for liquids which do not attack mercury. 



Three series are recorded below. No. 19 was made by the first 

 method, and Nos. 20 and 21 by the second method. The correspond- 

 ing glass jackets were II and IV, containing when full 437 and 291.6 

 grams of mercury respectively. The weights of water were 4.165 and 



