in the Analogy between Solutions and Gases. 87 



state is maintained during equal alterations of temperature. 

 It has been proved by physiological methods by Donders and 

 Hamburger ( Onderzoekingen gedaan in het physiologisch. La- 

 boratorhtm der Utrechtsche Hoogeschool [3] ix. p 26), making 

 use of blood-corpuscles, that solutions of potassium nitrate, 

 sodium chloride, and sugar, which at 0° are isotonic with the 

 contents of these cells, and hence are isotonic with each other, 

 exhibit the same isotonic state at 34°; this is seen in the 

 annexed table : — 



Temperature 0°. Temperature 34°. 



KN0 3 ■ • 1-052 to 1-03 p. c. 1-052 to 1*03 p. c. 



NaCl . . . 0-62 to 0-609 p. c. 0'62 to 0*609 p. c. 



C 12 H 22 O n . . 5-48 to 5-38 p. c. 5-48 to 5*38 p. c. 



Experimental Proof of Boyle's and Gay-Lussac's Laws for 

 Solutions. Experiments by Soret (Archives des Sciences phys, 

 et nat. [3] ii. p. 48 ; Ann. Chim. Phys. [5] xxii. p. 293). — 

 The phenomenon observed by Soret lends a strong support to 

 the analogy between dilute solutions and gases in respect of 

 the influence of concentration and temperature on pressure. 

 His work shows that just as in gases the warmest part is the 

 most rarefied, so with solutions the warmest portions are the 

 most dilute ; but that in the latter case a much longer time 

 must be allowed for the attainment of equilibrium. The ex- 

 perimental apparatus consisted of a vertical tube, the upper 

 portion of which was heated while the lower portion was kept 

 at a low temperature. 



Soret's latest experiments lend a quantitative support to 

 our analogy. As with gases, it is to be expected that when 

 the isotonic state is produced, the solution will exist in 

 equilibrium; and as the osmotic pressure is proportional to 

 concentration and to absolute temperature, the isotonic state 

 of different portions of the solution will occur when the 

 product of the two (absolute temperature and concentration) 

 are equal. If we therefore calculate, on this basis, the con- 

 centration of the warmer part of the solution from data 

 obtained with the colder, the values compare with those 

 found as follows : — 



1. Solution of Copper Sulphate. — The portion cooled to 20° 

 contained 17*332 per cent. The hot portion at b0 Q should 

 contain 14 '3 per cent. ; found, 14*03 per cent. 



2. The portion cooled to 20° contained 29*867 per cent. 

 The portion at 80° should contain 24*8 per cent. ; found, 

 23*871 per cent. 



It must be stated that previous experiments by Soret gave 

 less favourable result.- ; yet perhaps too much importance 



