508 



EEPORT — 1888. 



which, in the liquid state, conform to MendelejeflP's law with sufficient 

 accuracy, and of which the critical temperatures also are known ; if the 

 values of a so found are nearly equal we have a strong confirmation of the 

 relation between Ic, a, and T, expressed in equation (n). 



The relation between the volumes at t° and 0° (ordinary scale, air- 

 thermometer) is that 



?'«_aTi-273 



whence, if ro=l, 



vo aTi-T ' 



_ Ti;,-273 

 ""T,(t-.-l)' 



the equation by which the values of a may be obtained. 



The authors give a number of tables of values of t or (T — 273) and 

 t', for differeut liquids, for which in each table the critical temperatures 

 have been determined by some one observer, together with the value of a 

 in each case. The table annexed — Table 1, p. 138 — in which the critical 

 temperatures have been determined for all the bodies by Sajotschewsky,' 

 is a good illustration : — 



The letters P, K, T indicate that the expansions were determined by 

 Pierre, Kopp, Thorpe. The mean value of a is found to be 1-995, which, 

 nearly agrees with each individual value. 



Other tables are given, in which critical temperatures are made use of 

 -n-hich had been found by Ramsay ^ and Pawlewski.^ The result of all 

 the determinations is to show that a differs from 2 by a very small frac- 

 tion. For a perfect liquid (i.e., where h is constant) we have, at constant 

 pressure — 



From equation (a) we have now — 

 l/fc=2T,-273 . 



(/3) 



a formula by means of which, in the case of a volatilisable liquid gene- 

 rally, the critical temperature can be calculated from observations on its 

 ' expansion ' as a liquid. 



On page 144 is given a table of the observed absolute critical tempera- 

 tures of the bodies in the table cited, and by side of these the calculated 

 critical temperatures. The correspondence is so close that it is worth, 

 while to reproduce the table here. 



' Wied. Beihl. 1879, p. 741. = Proc. Roy. Soc. 31, 194. 



« Ber. 15, 1882, p. 2450 ; 16, p. 2633. 



