BRIDGMAN. — A DETERMINATION OF COMPRESSIBILITIES. 279 



pressures. He finds, e. g., for the compressibility of water at 200 and 

 400 kgm. 42.5 and 39.6 respectively, against 42.4 and 40.6 as found by 

 Amagat. This points, therefore, to an error in Richards' standard in 

 the right direction, and of approximately the right magnitude to bring 

 his result into agreement with the above. It may also be remarked in 

 this connection that the quantity c is essentially a difference of the 

 second order, and that consequently any increase of the pressure 

 range will give a more than proportionate increase in the probable 

 accuracy of c, other things being equal. 



The form of steel piezometer described above may be applied with 

 a few obvious modifications to the determination of the compressi- 

 bility of other liquids than mercury, and even of liquids that attack 

 the steel. In fact, it seems probable that some such form will prove 

 most useful for high pressure work in general, because the forms of 

 glass piezometer in common use become impracticable at high pres- 

 sures by the cracking of the glass around any pieces of sealed-in plati- 

 num, or even by the cracking of the glass alone, when blown into at 

 all complicated shapes. 



Conclusion. 



In this paper there have been presented methods applicable over 

 a wide pressure range for finding the compressibility of solids in the 

 form of rods or tubes, and also of liquids. These methods have been 

 applied to the determination of a few compressibilities which were 

 needed for another purpose. The pressure range employed was 

 6500 kgm. The compressibilities found were as follows : two pieces 

 of Jena glass 



No. 3880 a, 2.17 X 10"* kgm. per sq. cm. 



No. 3883, 2.23 X 10- 6 kgm. per sq. cm. 

 Four pieces of steel: two of Bessemer boiler plate, one of Bessemer 

 rod, and one of tool steel, respectively, 



5.298 X 10- 7 , 5.303 X lO" 7 , 5.16 X 10~ 7 , and 5.25 X 10~ 7 . 



Another piece of Bessemer by an indirect method, not so accurate, 

 gave 4.7 X 10 — 7 . Compressibility of commercial aluminum rod, 

 11.7 X 10 — 7 . The change of volume of mercury is connected with 

 pressure by the relation 



— = bp+ cf 

 ¥ o 

 b = log" 1 (4.5681 - 10) ; 



- c= log" 1 (9.2977 - 20). 



