486 



C. Barus — Fluid Volume and its 



Hence, instead of introducing arbitrary considerations I re- 

 solved to neglect the correction altogether, in favor of direct 

 test experiments made with mercury and water. The com- 

 pressibility of mercury is two small to be measurable by the 

 present method. Hence, since its compressibility is known, it 

 is well adapted for testing the errors of the apparatus. 



In table 3 I have given the temperature, #, and the length, 

 Z, of the mercury thread observed ; also the volume decrement 

 v/ V per unit of volume, for each pressure p, as well as the 

 corresponding mean compressibility /?. Many methods were 

 tried, but the best results were obtained with a thread of mer- 

 cury enclosed between end threads of paraffine. At the low 

 temperature, 30°, the lower thread was alcohol. At high tem- 

 peratures the greatest care must be taken to free the thread 

 from adhering air bubbles, or of globules of volatile liquid, 

 for in expanding they utterly vitiate the results, as I found in 

 more than one instance. 



Table 3. 

 Compression of mercury to test tubes. 



1 





v 









v 





<u . 



P 



-X1Q3 



/?xl0 6 



e,L 



P 



-X103 



/3xl0 6 



30° 



20 









185° 



20 



•o 





16'7 cm 



100 



•2 



2 



17'l cm 



100 



1-1 



14 





200 



•3 



2 





200 



2-2 



13 





300 



•7 



3 





300 



2-6 



9 





400 



1-5 



4 





400 



4-2 



11 





mean 





3 





mean 



m 



12 



65° 



20 



~ : o" 







Another 



thread 





16-8 cm 



100 



•6 



8 ; 

 14 



185° 



20 



•0 







200 



2-0 



19'3 cm 



100 



•8 



10 





300 



2-0 



8 





200 



30 



17 





400 



3-0 



8 



' 



300 



3'8 



14 





mean 





9 





400 



4-7 



13 



1C0° 



20 



•6 



.. 





mean 







13 



16-9 cm 



100 



•7 



10 



310° 



20 











200 



1-5 



9 



19-7 cm 



100 



1-2 



15 





300 



2-5 



8 



1 



200 



2-6 



14 





400 



2-1 



8 





300 



4-0 



15 





mean 



--- 



9 





400 

 mean 



53 



14 



JL5 



This table is reassuring. From the known low temperature 

 compressibility of mercury,* it appears that the error of ft 

 made by neglecting T ait's correction is of the order of 10 ~ 8 , 

 and that it is not greater than the unavoidable errors of meas- 

 uiement. Again since the compressibility of the organic sub- 

 stances examined as in all cases much greater than 60 X 10~ 6 , 



* Everett: 1. c, pp. 52. 53. Cf. Amagat: C. R. cviii, p. 228, 1889; Journ. de 

 phys., (2), viii, p. 197, 1889; Tait: 1. c. 



