( 778 ) 



§ 2. Reduction of the readings of the hydrogen thermometer of 

 constant volume to the absolute scale. 



If v is the volume of the gas in the thermometer, expressed in 

 the theoretical normal volume, /> the pressure in atmospheres, 7 7 the 

 absolute temperature, the equation of state for the thermometer gas 

 may be written in the form : 



/ B't C't\ 

 pv = A T 1+-A + — i) (2) 



\ V V J 



Further we put : 



/ the temperature on the scaie of the hydrogen thermometer of 

 constant volume 

 and 



t is determined by 



T — 7' o c. = 6. 

 (pv)T—(pv) 



(F')o a p 



where a p represents the mean pressure-coefficient between 0° and 

 300° for the thermometer with the specific volume v. This is given 



, Wipo — OH 

 J I00(pv) * 

 If we represent the correction on the absolute scale by : 



A t = 6 — t, 

 we may write for this : 



(T T) ( T m B' m -T B '„ T m C' K0 -T o C '^ , TB<r-T B< n TOr-T n C' n \ 

 t _ o) \ 1D0« "*" 100 ü 2 / V v ^ v" / 



. , Aoo^'ioq— ^'o^'o , ^ï oo^'ioo — ^o^'o 

 ~*~ 100 v + 100 1>2 



In agreement with what may be derived from the mean equation 

 of state VII. 1, it appears from our determinations, that the influence 

 of C' t is very slight, and down to — 217° does not amount 

 to more than 0°.0003, so that it has not to be taken into 

 account. Therefore in what follows will be put Ct = 0, as is also 

 done by Berthelot but without proof. 



For the absolute zero point the value 273°. 09 l ) is assumed, from 



l ) From Amagat's experiments with the development into series of Comm N°. 71 

 (cf. the note to § 12 of Comm. N n . 97«) 1.26X10—5 was found for the difference 

 between the pressure-coefficients of nitrogen at 1000 mm. pressure and mm. pres- 

 sure, from which follows with Chappuis' pressure-coefficient for 1000 niM., i. e. 

 0.0036744 the value 0.0036618 for the limiting value at mM. pressure, corresponding 

 to the absolute zero point — 273°.09. In the same way hydrogen gives for the 

 difference of the pressure-coefficients at 1090 mM. and mM. 2.1 X 10—6, which 

 with the pressure-coefficient 0.0036629 given in Comm. N°. 60 (see XV) gives 



