254 Mr. C. Tomlinsou on the Cohesion-Figures of Liquids. 



sulphuric acid, and then in a solution of caustic potash. If, after 

 this, the water completely wet the glass, it may be rinsed and 

 used. It had better not be wiped. Having been once washed 

 with sulphuric acid, it will serve for a great number of experi- 

 ments, provided it be washed in a weak solution of caustic pot- 

 ash after each experiment, and rinsed with clean water. The 

 substance of which the figure is to be determined must, as already 

 remarked, be pure : the figure given by pure washed ether becomes 

 changed into the perforated discs by the addition of a few drops 

 of absolute alcohol to a small quantity of the washed ether ; and 

 the unwashed ether, if exposed in an open vessel for a few mi- 

 nutes, will throw off its ethereal portion, and the cohesion-figure 

 will quickly pass into the alcohol figure. It is quite remarkable 

 how rapidly this change takes place. I bad poured some un- 

 washed ether into a test-glass, from which I fed the dropping- 

 tube, and in about ten minutes the ether figure was completely 

 superseded by the alcohol one. I do not pretend to say that all 

 the substances made use of in this inquiry are pure. I have 

 taken pains to procure them from the best sources, such as the 

 manufacturers themselves ; but some of the essential oils, for 

 example, are prepared on the Continent, and may possibly not 

 be quite pure. 



There is not so marked a difference between the cohesion- 

 figures produced by spirits of wine and absolute alcohol as 

 between unwashed and washed ether : nor is this to be wondered 

 at, seeing that spirits of wine only differ from absolute alcohol 

 in having already received a portion of the water which the abso- 

 lute alcohol takes up in forming its peculiar figure on water. 

 The figure of spirits of wine consists of a central disc with a 

 foliated outline surrounded by a tolerably smooth disc. The 

 figure of absolute alcohol (PI. IV.) has the central disc more 

 minutely foliated than in the former case, and it has a greater 

 tendency to a stellar arrangement. 



Without further multiplying these examples, I may once 

 more recur to the law on which they seem to rest — viz. that each 

 figure is the resultant of the cohesive force of the liquid, its den- 

 sity, and the adhesion of the receiving surface. If this be true, 

 it follows that two liquids although of very different chemical 

 character, yet being of the same density, similarly cohesive, 

 whether viscid or fluid, and the adhesion of the receiving surface 

 being the same (*. e. having the same degree of solubility), we 

 get precisely the same cohesion-figures for both liquids. Now 

 creosote and oil of cloves are chemically two very dissimilar 

 liquids. It is true that both are hydro-carbons, and that each 

 consists of two distinct bodies; but their points of difference arc 

 numerous and important. Nevertheless their physical resem- 



