292 report — 1859. 



of the phenomena of solution which these experimenters exhibit, we may 

 expect most important results from their labours. 



The graphic coordination of the results of experiments on the solubility of 

 salts which have hitherto been recorded, lead to this capital fact, that within 

 the limits of temperature embraced by the experiments, soluble salts may be 

 classified into three groups : — 1, those which, like sulphate of soda, attain a 

 maximum of solubility within those limits, that is, give an ascending and 

 descending curve; 2, those which, like common salt, have sensibly the same 

 solubility at all temperatures within the limits ; and 3, those which, like 

 nitrate of potash and the majority of salts, increase considerably insolubility 

 as the temperature rises. The fact of certain salts, such as sulphate and 

 carbonate of soda, exhibiting a point of maximum solubility, or, as Lowel 

 has shown, several such points, according to the modifications which take 

 place in their molecular states, naturally suggests the probability that most 

 salts would exhibit a point or points of maximum solubility, and a descending 

 as well as an ascending curve of solubility, if we were to extend the range 

 of our experiments to sufficiently high temperatures, provided they could 

 resist without decomposition or volatilization such temperatures. And 

 further, that many salts more or less soluble at common temperatures, may 

 become wholly insoluble at high temperatures. In the case of sulphate of 

 lime, the latter fact has been established by the observations of M. Couche 

 and myself. From some preliminary experiments which I have since made, I 

 think I shall be able to establish it in the case of many other salts likewise. 



Although water under sufficient pressure retains its liquid form at tem- 

 peratures far above 100°, the experiment of Cagniard de la Tour shows 

 that if the temperature be raised sufficiently high cohesion will ultimately 

 disappear, and the water will pass without alteration of volume into gas of 

 enormous tension. Frankenheim and Brunner have both found that the 

 elevation of water in capillary tubes decreases with the temperature, and that 

 it is capable of being represented by a very simple formula of interpolation 

 as a function of the temperature. If this formula were to hold approx- 

 imately true at very high temperatures, it would enable us to trace the 

 diminution of the cohesion as the temperature rises, until it would wholly 

 vanish, which on this hypothesis would take place, according to Brunner, 

 at 535 0, 38. Cagniard de la Tour made similar experiments upon some other 

 liquids with like results. He found that the total gasification of ether took 

 place at about 200°. The temperature at which the capillary height of ether 

 would be zero, calculated by Brunner's formula, would be 191°'12. Wolf 

 has experimentally found* that the capillary height was reduced to zero at 

 190° or 191°; above that temperature the capillary meniscus was below the 

 level of the liquid, that is, there was capillary depression. At about 198° the 

 strongly convex surface of the liquid appeared to cover itself with a thick 

 cloud : at about 200° it was wholly changed into vapour. This striking 

 coincidence between the calculated and experimental results, M. Wolf con- 

 siders to be only accidental. Brunners formula was founded upon experi- 

 ments made within the limits of temperature of 0° to 35°, a range which 

 M. Wolf thinks too limited. He has found, that, although the law of Brun- 

 ner, that the decrease of the capillary height is proportional to the tempera- 

 ture, holds true up to 100°, it becomes more rapid above that point. What- 

 ever may be the exact law for high temperatures, enough has been done to 

 show that the decrease of capillarity may be employed as a measure of the 

 diminution of cohesion at high temperatures. I think we may safely con- 



* Ann. de Chim. et de Phys. vol. xlix. p. 230. 





