BETWEEN ONE ATMOSPHERE AND HALF AN ATMOSPHERE OF PRESSURE. 367 

 The equation which best represent*} the relation of d(irv)/<ln to temperature is 



dw 

 corresponding to the pressure- equation for Imp deiixitiex 



Also 



1 d(m>) _ 9 / 6\ 

 irv dit ' 1280\ ~ 0V' 



As an example, let us apply this formula to find for oxygen what change must be 

 made in a in order to pass from the temperature of the observations ( 1 r2 C.) to C. 

 If 0,, lie the value of for C., we have 



ff 978 978 f) 878+11-8 884-8 



~973-118~~155 155 155' 



The factor by which the observed value of a must be multiplied is thus 



Q -i-60 - 3 

 0-i - 6 0- 8 



being the same whether the pressures be reckoned in terms of the critical pressure or 

 in atmospheres. In the case of oxygen the factor is 



568-1-097 _ -599 _ 

 " -488 " 



The observed value of a is '00076, corresponding to 11 '2 C. Hence at C. we 



should have 



a= -00076X1-236 = -'00094. 



It will be seen that the correction has a considerable relative effect ; but a is so 

 small that the calculated atomic weights are not much influenced. It must be 

 admitted, however, that observations for the present purpose would be best made at 

 C. ; to this, however, my apparatus does not lend itself. 



The following table embodies the results thus obtained. 



