Mr. C. Tomlinson on the Cohesion-Figures of Liquids. 251 



substances that produce them ; and so sensitive are they to any 

 variations in the conditions under which they are produced, that 

 a slight alteration in one of those conditions leads to a marked 

 change in the cohesion -figure. Thus the cohesion-figure of wood- 

 spirit on water is very different from what it is on mercury, since 

 the surface attraction or adhesion of mercury is very different 

 from that of water. 



Now let us examine the cohesion-figure of a liquid that is 

 sparingly soluble in water, such as creosote. If we deliver a drop 

 of this substance from the end of a glass rod to the surface of 

 one ounce of water, we may witness a struggle between cohesion 

 and adhesion that will last about five minutes. The creosote 

 sails about on the surface of the water in a state -of considerable 

 agitation, discharging a number of small globules on all sides,, 

 which, in their turn, are greatly agitated ; they rotate and dis- 

 appear, leaving behind them a thin silvery film. Meanwhile the 

 parent globule diminishes in size, but preserves all the charac- 

 teristics of its cohesion-figure, until at length it disappears in 

 the form of a film. If a second drop of creosote be now placed 

 on the water, its behaviour will resemble that of the first in a mi- 

 tigated form; it will be much less energetic, and will last a 

 much longer time before it disappears in the form of a film. A 

 third drop will remain on the surface in the form of a double 

 convex lens sharply defined, showing that the cohesion of the 

 creosote exactly balances the adhesion of the water ; or, in other 

 words, that saturation has been attained. If we now add more 

 water, or increase its solvent power by the addition of a drop of 

 acetic acid, the action will set in again, and the lens will change 

 into the cohesion-figure. (See Plate.) 



The following comparative experiment was made with fresh 

 colourless creosote (Morson's) in two exactly similar shallow 

 glasses, one containing one ounce, and the other two ounces of 

 New River water. In such water adhesion is diminished by its 

 mineral contents. In distilled water the phenomena are the 

 same, but the time is diminished, a drop of creosote disappear- 

 ing in five minutes instead of seven : — 



Glass No. 1. — 1 oz. water. 

 First drop of creosote disap- 



Second drop disappeared in.. 

 But two or three minute 

 specks of creosote remain- 

 ed, moving in circular orbits 

 in the film. 



mm. 



7 

 20 



S3 



Glass No. 2. — 2 ozs. water. 



min 

 First drop of creosote disap- \ I 



peared in J 



Second drop disappeared in.. 12| 

 The disc was flatter and 

 more vigorous than in 

 No. 1 ; towards the end the 

 disc broke up into separate 

 portions, which rotated 

 with immense rapidity and 

 disappeared. 



