U 36 Mr. J. Rose- Lines on the Practical Attainment of 



numerical expression on the thermodynamic scale. The ques- 

 tion of how to do this resolves itself into two minor problems: 

 (i.) To find the absolute value of the freezing-point of water; 

 and (ii.) to find the value of the interval between the 

 freezing-point of water and the temperature under discussion. 

 These two problems are fairly distinct, though not entirely 

 so ; and the first of them will be investigated in the present 

 Section. 



We start with the equation 





Let us now imagine that we keep v constant ; let the suffix 



applied to p and t refer to the freezing-point, and the suffix 



1 to the boiling-point, then 





Hence 



PiV 



Multiply the first of these equations by * 1? the second by 

 t , and subtract 



(m-m>= -? {? «.-id+?£ -It)}. 



e 



M-M-g{f(wj + f(^^)}; 



°~ P °Pi-Po vHpi-Po) 12 3 U tj J 



-jPo r 



1 (^Wi+LU 



The expresssion p gives us the " uncorrected 



Pi—Po 

 estimate" of t ; that is, the estimate of t that would serve if 

 the gas could be treated as a perfect gas. The expression 



p l2 T 3A*o <i/J 

 gives us the correction required in the estimate owing to the 



