12 THE VOYAGE OF H.M.S. CHALLENGER. 



The following are some of his results for water : — 



Temperature. Compressibility per atm. 



0"-0 C. 0-0000503 



l°-5 515 



4°-l 499 



10° -8 480 



18°-0 462 



25°-0 456 



34°-5 453 



53°-0 441 



These numbers cannot be even approximately represented by any simple formula ; 



mainly in consequence of the maximum compressibility which, they appear to show, lies 



somewhere about 1°"5 C. No other experimenter seems to have found any trace of this 



maximum. 



Grassi assigns, for sea-water at 17°"5 C, 0'94 of the compressibility of pure water, 



and gives 



0-00000295 



as the compressibility of mercury. He also states that the compressibility of salt solu- 

 tions increases with rise of temperature. These are not in accordance with my results. 

 But, as he further states that alcohol, chloroform, and ether increase in compressibility 

 with rise of pressure (a result soon after shown by Amagat to be completely erroneous), 

 little confidence can be placed in any of his determinations. 



A very complete series of measurements of the compressibility of water (for low 

 pressures) through the whole range of temperature from 0° C. to 100° C, has been made 

 by Pagliani and Vincentini. 1 Unfortunately, in their experiments, pressure was 

 applied to the inside only of the piezometer, so that their indicated results have to be 

 diminished by from 40 to 50 per cent. The effects of heat on the elasticity of glass are, 

 however, carefully determined, a matter of absolute necessity when so large a range of 

 temperature is involved. The absolute compressibility of water at 0° C. is assumed from 

 Grassi. The following are some of their results, showing a much larger temperature 

 effect than that obtained by Grassi : — 



Temperature. Compressibility per atm. 



0°-0 C. 0-0000503 



2°-4 496 



15°-9 450 



49°-3 403 



61°-0 389 



66°-2 389 



77° -4 398 



99"-2 409 



1 Sulla Comjtressibilila del Liquidi, Torino, 1884. 



