38 Mr. W. Swan on certain Phenomena of 



given in Dr. Wilson's paper, it will be observed, that when 

 the liquids have a decided chemical affinity for each other, 

 their mutual surface is flat, as in the case of the fixed oils with 

 solution of potash, and the essential oils with alcohol ; while 

 the curved surface is assumed by liquids whose chemical affi- 

 nity is either extremely feeble or entirely wanting, as is the 

 case with the oils in contact with water or acids. The expe- 

 riments therefore confirm Dr. Wilson's opinion, that the flat- 

 ness of the surface results from the chemical affinity of the 

 liquids ; and it is therefore probable that this effect is due to 

 a strong mutual attraction of their particles. 



But before coming to this conclusion, it will be proper to 

 examine other explanations of the phenomenon which may 

 suggest themselves. It might be supposed that the liquid 

 which possesses the highest attraction for glass, or wets it 

 most readily, will, in contact with a liquid whose attraction 

 for glass is not so great, have the effect of rendering the sur- 

 face of the less wetting fluid convex, by forcing itself between 

 it and the walls of the containing vessel. On this supposition, 

 the greater the difference between the attractive powers of the 

 two liquids for glass, the greater will be the curvature of their 

 mutual surface ; while a surface nearly flat will indicate a 

 nearly equal attraction of the two liquids for glass. As the 

 addition of hydrochloric acid renders the flat surface of chlo- 

 roform under an alkaline solution convex, the recession of 

 the chloroform from the walls of the vessel, which is necessary 

 to its becoming convex, would be attributed to the attraction 

 of the acid for the glass enabling it to insinuate itself between 

 the glass and the chloroform to a greater extent than the 

 alkali; and it would necessarily follow, that the attraction of 

 the acid for glass is stronger than that of the solution of pot- 

 ash. But it will be seen from the following experiments that 

 the contrary is the case. 



Having carefully ascertained the specific gravities of the 

 solution of potash, the hydrochloric acid, and the chloroform 

 I had used in my experiments, I observed the heights at which 

 they stood in a thermometer- tube 0*01 4- of an inch in diameter. 

 The following table exhibits the mean of six observations with 

 each liquid. 



Specific gravity. Height in tube. Constant*. 



Chloroform . . l'493f 08 of an inch. -Oil 



Solution of potash 1-34.3 2*9 ... *041 



Hydrochloric acid 1*165 2'7 ... '038 



* This number, obtained by multiplying the diameter of the tube by 

 the height to which the liquid rises, is always the same for the same liquid, 

 and is given here in order to check the accuracy of the experiments, 

 f As the specific gravity of chloroform has been generally stated at 1*480 



