496 



C. Barus — Fluid Volume and its 



Method op Discussion. 

 25. Isothermal hand. — Having given certain corresponding 

 values of pressure and volume obtained at any given tempera- 

 ture, let a close-fitting function 

 be investigated, such that for the 

 same pressures, the calculated 

 values of volume decrement must 

 eventually be greater than the 

 observed decrements will be. 

 - Let another function be inves- 

 "V-~ Jvr tigated, such that for the same 



pressures, the calculated values 

 of volume decrement must event- 

 ually be less than the observed 

 values will be. From the nature 

 of the variation, the observed or 

 actual relation between volume 

 and pressure will probably lie 

 within the band or pathway in- 

 cluded between the two limiting 

 functions in question. 



Suppose it is possible (the 

 proof must be given by trial) to 

 so adjust the two functions, that 

 throughout the interval of obser- 

 vation they both fall within the 

 limits of error. Then any prop- 

 erty which is simultaneously pre- 

 dicted by both functions, may 

 confidently be assumed as the 

 property of the unknown iso- 

 thermal. So long as the func- 

 tions do not diverge seriously, 

 there is here given a judicious 

 mode of extrapolation, by which 

 relations beyond the limits of 

 experiment may be apprehended. 



26. Quadratic constants.— In 

 order to arrive at the probable 

 nature of such functions, I passed 

 parabolas through the observa- 

 tions. The ordinary vertical 

 parabola is clearly inapplicable. 



Fig. 2.— Isothermal decrements of para- It predicts a maximum and is 



toiuidine, referred to unit of volume therefore not compatible with 



at 20 atm. and the respective isomer- ,, -, i .c j at 



. mal temperatures. tlie locus to be found - -Never- 



Fig. 3.— isopiestic increments of para- theless the zero-compressibility 

 toiuidine, under the same conditions. mav thus be deduced, and from 



the relation of the two constants 



a, region of undercooling. 



