242 



Mr. William Sutherland on the 



account of the experimental difficulties hitherto met with in 

 the measurement of /jl, the equation gives no very delicate 

 test, although it might with the improvements in accuracy 

 made within the last few years. In addition to ethyl oxide, 

 the two substances for which we have measurements of both a 

 and fj, over the widest range of temperature are ethyl chloride, 

 studied as to expansion by Drion and as to compression by 

 Amagat, who has corrected Drion's coefficients of expansion 

 for change of pressure, and pentane, studied by Amagat and 

 Grrimaldi. The following are the values of I calculated from 

 the data at different temperatures for these two substances, 

 with the megadyne taken as unit of force. 



I 



| Temperature C. .. 



0°. 



11°. 



13°. 



20°. 



40°. 



60°. 



80°. 



100°. 



5 H 12 (Grimaldi).. 

 C 3 H 12 (Amagat) .. 

 CLH-C1 



! 8530 



5820 



... 



9200 



... 



7430 



7230 



8000 

 5450 



8300 



9250 

 9250 

 5270 





This comparison has been made to show how, from mea- 

 surements of liquid compressibility at present available, we 

 can get only a fair idea of the value of I, but not an accurate 

 measurement of it. 



Amagat has determined the compressibility of several other 

 liquids at different temperatures (Ann. de Chim. et de Physique, 

 ser. 5, t. xi.) ; so have Pagliani and Palazzo (Wied. Beibl. ix.J 

 and de Heen (Wied. Beibl. ix.), but their discussion would 

 bring out nothing more than the above comparison has. De 

 Heen's results would appear to make I diminish with rising 

 temperature nr every case ; but he measured his com- 

 pressibilities in comparison with that of water at the same 

 temperature, and to calculate their values used Pagliani and 

 Vincentini's values for water (Wied. Beibl. viii.), which make 

 the compressibility of water much more variable with tem- 

 perature than Grassi's. If we used Grassi's values in 

 de Heen's experiments, I would remain nearly constant. 

 We will accordingly use the compressibility-method of cal- 

 culating / subsequently, only to illustrate the general agree- 

 ment of. values derived from purely mechanical experiments 

 with those found by the more accurate methods to which we 

 now proceed. The values found by this second method are 

 tabulated later on in Table XXIY. 



Third method of finding the virial constant I : from the 

 latent heat. If we differentiate with respect to T our equation 



