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



long, ragged, irregular, oily-looking smears — an effect which is 

 characteristic of oil of almonds. 



Alcohol is also used to adulterate the essential oils : its pre- 

 sence can be detected by phenomena which vary with the pro- 

 portions used. There are also special phenomena with each oil, 

 that would take a long time to describe. 



The films formed by such common oils as sperm and colza are 

 also characteristic. Sperm oil forms a smooth large film, which 

 occupies the whole surface and is accompanied by iridescent 

 rings, which disappear when the film is formed. Minute and 

 nicely perforated holes open in the film, and after a short time 

 long, thin, narrow cracks open in it, darting out from the holes 

 and often connecting them together like beads on a thread. 

 These cracks are characteristic of sperm oil. (See Plate.) 



Colza oil forms a large smooth film, accompanied by iride- 

 scent rings, which immediately disappear. Minute holes open 

 at the edge at intervals, three or four together, sharp and clean 

 as if punched. Similar distinct perforations are also formed in 

 other parts of the film ; and these widen and thicken at the edges 

 until the surface is covered with a kind of honeycomb-pattern, 

 the holes pressing together in twos and threes. The character- 

 istic feature of the colza film is to be found in these large holes 

 with thickened edges grouped together and opening into each 

 other. After about an hour the film becomes whitish and greasy- 

 looking, and the holes are surrounded by dark rings. It may 

 be remarked, however, that an increase of temperature quickens 

 and exalts the phenomena of this and other films. Thus the 

 effects are more numerous and more quickly brought about on 

 a fine warm day than on a dull and cloudy one. The films should 

 also be formed on a given fixed area of water, or the film of the 

 same liquid may vary in thickness at different times and thus 

 disturb the phenomena. I have found a conical foot-glass nearly 

 4 inches in diameter at the mouth, nearly filled with water, 

 answer well. 



A mixture of sperm and colza in various proportions forms a 

 good film, in which may be recognized the cracks of the sperm 

 and the peculiar holes of the colza. I think it would be easy for 

 any one to detect the mixture of these two oils by the character 

 of the film. (See Plate.) 



I have thus briefly indicated the mode of obtaining these 

 cohesion-figures, and their value in determining the nature and 

 purity of various liquids in common use and which are liable to 

 adulteration, such as sulphuric ether, the essential and fixed oils, 

 &c. By simply noticing the cohesion-figure of sulphuric ether 

 for example, we can decide whether it contains alcohol or not. 

 I believe it would be easy in many cases to decide by this mode 



