THERMAL PROPERTIES OF CARBONIC ACID AT LOW TEMPERATURES. 



75 



so found we have the gas-limit curve. The diagram might be completed by adding 

 the I lines, &c., but it will be convenient to consider first the modifications required 

 to allow for the changes of volume of the liquid CO, which have so far been 

 neglected. 



Fig. 7 represents the same diagram as fig. 2 with the addition of some lines to 

 show the effects of the dilatation and elasticity of the liquid. 



Let AHK be the constant-pressure line through A, in the liquid area, 



Let GA represent the limit curve as before, 



Let GK be the constant I line through G, meeting AHK in K. 



The heating of the liquid CO, in Series II. experiments is now represented by the 

 line KA, instead of by GA. 



The true value of L is found as follows : 



L = GN + BQ EQ as before; also BQ and EQ are given, as before, by Series I. 

 and III. experiments, but GN is no longer I, I,. We now have 



GN'= I B -I G) 



= IA IK, since AB and GK are constant I lines, 



= (I, I,) + (I, 1 4 ), using suffixes to refer to the temperatures # 0,, and 4 . 



I, I;, is read off the I curve as before, but I, I 4 can only be read off the curve 

 when 4 is known. The quantity I 3 1 4 may be regarded as a small correction to be 

 applied to the approximate value of L to allow for the elasticity and dilatation of the 

 liquid. 



Series IV. experiments were made to determine the difference of temperature 

 d a O t between H and K, i.e., the Joule-Thomson effect for the pressure drop Pi~p 3 . 

 It was observed directly by measuring the change of temperature as the liquid passed 

 through a throttle valve. The arrangement of the apparatus is shown in fig. 8. 



Fig. 8. 



A summary of the observations is given in Table V. The observations are plotted in 

 fig. 9 and a smooth curve drawn through them. The values of I, 1 4 calculated from 



L 2 



