Spread of Liquids on Solid Bodies. 417 



away from a glass surface ; the contrary must occur according 

 to Table VIII. 



In fact the first occurs, since, as I formerly* proved by 

 the change of height of capillary ascent, in a capillary tube 

 filled with olive-oil and dipped in turpentine, the latter drives 

 away the olive-oil, and finally spreads upon the surface of the 

 olive-oil. 



In the case of all aqueous saline solutions which are mis- 

 cible with water in all proportions, the saline solution must 

 drive away the water from the surface of the glass the more 

 easily the more concentrated it is, since (a) increases f with 

 augmented concentration, and, as is shown in detail in § 9, 

 a 12 is the smaller as (a) = « 2 cos 6 is greater for the free 

 surface of the liquid. 



The same must also occur in the case of different saline 

 solutions which are miscible in all proportions, and which 

 exercise no chemical action upon one another (as giving pre- 

 cipitates &c). 



Since for all saline solutions the edge-angle against glass 

 has nearly identical values, the saline solution with the greater 

 cohesion (a) will drive away from the surface of the glass 

 that with lesser cohesion. 



Hence it follows, further, that from a dilute saline solution, 

 as a mixture of water of less cohesion with concentrated saline 

 solution of a greater, there must collect on the surface of the 

 glass a concentrated solution. The most soluble substances, 

 which in strong concentration exhibit the greatest cohesion, 

 must also collect specially readily on the surface of glass, or 

 will be specially strongly absorbed by the glass surface. 



The phenomena of so-called selective absorption appear to 

 confirm this. Quartz, porcelain, &c, which have for saline 

 solutions an edge-angle similar to that of glass (compare § 7 

 above), appear to absorb carbonate of potash, chloride of 

 calcium, chloride of magnesium, &c. specially strongly, and 

 hence, therefore, those salts which with strong concentration 

 exhibit the greatest cohesion (<*). 



This is in harmony with experience in the fact that new, 

 unused porcelain cylinders (such as are usually employed in 

 galvanic batteries), when they have once been in contact with 

 a dilute saline solution, retain salt absorbed even after a long- 

 protracted steeping in water. 



The influence of the molecular nature of the solid substance 

 exhibits itself specially clearly in the case of lightly and 



* Pogg. Ann. cxxxix. p. 55 (1870). 

 t Ibid. clx. p. 371 (1877). 



Phil. Mag. S. 5. Vol. 5. No. 33. June 1878. 2 E 



