130 Henry Riddell on 



One of the greatest of the French inventors in this development 

 of industry says — This remarkable scientific man very wisely 

 turned his attention to a simpler problem, that of the liquefaction 

 of Carbonic Acid, with a view to investigating its characteristics. 

 From this investigation • was destined to be born the general 

 theory of liquefaction and the ideas, more than ever prevalent at 

 the present time, on the Continuity of the Liquid and Gaseous 

 States." 



On hearing Andrews' paper shortly after the delivery of the 

 Bakerian lecture of 1869, the then President of our Society, 

 Joseph John Murphy, offered a suggestion for the calculation of 

 the critical temperature of water, rather interesting under the 

 circumstances. He argued that clearly the critical temperature was 

 that at which the latent heat of conversion to A'apour vanished. 

 " if, then, we accept Keynault's equation," said Mr. Murphy, 

 "throwing it into the form — Latent Heat = 606-5 - -695^, when the 

 latent heat vanishes we have •695^ = 606-5, or ^ = 873°C." Of 

 course this temperature is far too high, but the error was in the 

 equation and not in the method suggested. Reynault's equation 

 gave fair values at moderate temperatures between 100° and 200°, 



but the equation representing the facts has a factor ( 1 - - \ where 



t' = volume in liquid form and F volume of same quantity in 

 vapour, both taken at the temperature t. At 100° the term 



- has a value of about 0-0006, so that ( 1 - :r^) is very nearly 



V 



unity. At 200" the value of ^, is roughly 0-009, so that it is 

 rapidly increasing yet still nearly negligible. At a temperature 



V 



of about 250° the value of -r. has risen to about 0-025, while 

 V 



about 374" v becomes equal to F, and the Latent Heat becomes 



zero. Thanks to the introduction of quartz tul)es the critical 



point of water is measured fairly easily. 



In 1876 Dr. Andrews, in his second Bakerian lecture, gave 



