260 Mr. C. Tomlinson on the Cohesion-Figures of Liquids, 



to my view, do not act in preventing the exhibition of a new 

 force, but simply by preventing adhesion. Many of the pheno- 

 mena of cohesion-figures I have been unable to produce away 

 from home in vessels which have been cleaned and wiped in the 

 usual manner; but they have succeeded perfectly when the 

 glasses were washed in a weak solution of caustic potash and 

 rinsed in clean water. 



I have taken advantage of Ermann's observation to obtain on 

 mercury the cohesion-figures of sulphuric acid and other sub- 

 stances which act chemically when brought into contact with 

 water. In the case of sulphuric acid, the drop spreads instantly 

 and covers the surface of the mercury ; but cohesion immediately 

 begins to reassert its claims, and forms the acid near the edge 

 into large flat bosses, each of which becomes a centre of action ; 

 minute globules pass in and out of it; similar small globules 

 also move to and fro over the rounded edge of the mercury. 

 After a few minutes all action ceases : the film contracts with a 

 smooth surface and a well-defined edge. A drop of alcohol, or 

 of ether held over the sulphuric acid film when at its widest, 

 gathers it up in an instant into a small disc. The reason for 

 this is, that there is a much stronger adhesion between the acid 

 and the vapour of ether or alcohol, than between the acid and 

 the mercury. 



It was observed by Dutrochet that a drop of water placed on 

 mercury remains globular, an effect which he explains according 

 to his cpipolic theory. I explain it by the cohesion of the water 

 being stronger than the adhesion of the mercury ; and I imagine 

 that the absorption of water by the sulphuric acid film lessens 

 the adhesion of the mercury, aud enables cohesion to reassert its 

 claims with more effect. If the vessel be covered up, the diffused 

 sulphuric acid film is much more persistent. The superior cohe- 

 sive force of water is also shown by placing a drop of it on the 

 sulphuric acid film. It docs not spread, but remains in a very 

 convex lenticular state, at the same time repelling, apparently, 

 the sulphuric acid all around it, so that the lenticule of water 

 remains on a dry disc of mercury. These effects I attribute to the 

 stronger adhesion between the acid and the mercury than between 

 water and mercury. The water does not repel the acid, as Du- 

 trochet supposed, but simply absorbs a portion around it, suffi- 

 cient to allow it to rest on the mercury, and to prevent all further 

 action of the acid. 



The liquids whose cohesion-figures on water have been deter- 

 mined, present, of course, different figures on mercury, because 

 one of the conditions in the production of these figures (viz. the 

 adhesion) is no longer the same. Thus wood spirit, which on 

 water forms a figure something like that of alcohol, produces on 



