68 



Scientific Proceedings, Royal Dublin Society. 



M - m filled the apparatus to the division R. If the same bulb under the 

 same conditions of temperature and stem-exposure had been completely 

 filled with mercury, i.e. if the substance at T° C. had been replaced by mercury 

 at T° C, the mass of mercury in the apparatus filling it to li would have been 

 equal to 



Ma - Vt • Pt + {R - -So) 0-. 



Hence the volume Qij. of a mass W of the substance at 1'° 0. is equal to 

 the volume at T" C. of a mass of mercury equal to 



[ii/„ - V,, . p, + {R - R,) (7] - {31 - m), 

 or 



I r 1 



Qj. = — I M„- {M- m) - *v ■ Pj, + {R - R^) a , 

 Pt L J 



and for the volume of one gramme we have -r~. or 



F = 



W 



M„ - (.1/ - m) - Vj. . Pt + (R - Rf,) a 



If the original bulb had not been altered, and \i M = M„ the final 

 expression would have been simplified to 



1 r 



In tlie more general case, however, it will be noted that 



Mo - {M - m) - iv . pr 



will be constant during a particular test. If this constant {K) be determined 

 at first, the values of V, the volume of one gramme at a number of different 

 temperatures, can be readily calculated by such a tabulation as the 

 following : — 



General Remarks. 



The special advantages of the metliod above described are, first, that there 

 are no corrections to be applied for the expansion of the envelope, and no errors 

 due to exposure of stem outside the bath ; secondly, tlie shape of the dilate- 



