40 Mr. W. Swan on certain P/iccnomena of 



Another mode of accounting for the difference of the cur- 

 vatures in the two cases would be, to suppose a strong cohesive 

 attraction of the particles of the chloroform in comparison with 

 that of the particles of water or acids, and a nearly equal co- 

 hesive attraction in the particles of chloroform and alkaline 

 solutions. It is obvious that the more cohesive liquid would 

 tend to assume a spherical form; but in the case of liquids of 

 nearly equal cohesive power, it might be supposed that the 

 attracting forces, being nearly balanced, the resulting action 

 would be so small that their mutual surface would be nearly 

 flat. 



In order to estimate the cohesion of the liquids, I suspended 

 a glass disc an inch in diameter from one arm of a balance 

 capable of indicating 0*1 grain; and I found, by the mean of 

 several experiments, that it required 34*3 grains placed in the 

 opposite scale to detach the disc from the surface of hydro- 

 chloric acid ; while 33*1 grains detached it from the surface 

 of solution of potash, 38 grains from water, and 283 from 

 chloroform. 



As the disc separates from the surface wetted by the liquid, 

 it is obvious the separation must have taken place, not at the 

 surface of the glass, but in the body of the liquid, and hence the 

 cohesion of its particles must have been overcome by the weight 

 required to detach the disc. It would therefore appear that 

 the cohesive force of the particles of solution of potash and of 

 hydrochloric acid are nearly equal, while that of the particles 

 of chloroform is inferior to that of either of these liquids. A 

 similar result was also obtained by weighing a given number 

 of drops of those liquids. Twenty drops of solution of potash, 

 hydrochloric acid, and chloroform, weighed respectively 14*6, 

 16'9, and 11*3 grains. Since, then, the cohesive attraction 

 of chloroform is inferior to that of hydrochloric acid, it will 

 not account for its convexity in contact with that liquid ; while 

 the nearly equal cohesive powers of the acid and alkaline so- 

 lutions will as little explain the diversity of their action in the 

 presence of chloroform. 



As the flatness of the surface of the chloroform seems to 

 depend neither on the equality of the attractions of the liquids 

 for glass nor upon the equality of their cohesive attractions, it 

 next occurred to me to try whether the result was modified 

 by altering the nature of the containing vessel. I have found 

 that on immersing a slip of recently-ignited platina foil, or 

 clean iron or brass wire in the liquids, the surface of the 

 chloroform is highly convex in contact with them under water 

 or hydrochloric acid, but apparently flat under solution of 

 potash. If the metal is not perfectly clean, the surface of the 



