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



of oxygen, simple or ozonized, may prevent the display of these 

 characteristic phenomena ; but at the same time it will introduce 

 other results which are equally characteristic. 



Oil of turpentine is also used as an adulterant of the essen- 

 tial oils. Its presence can be detected by the brilliant iri- 

 descent colours which it imparts to films that are otherwise 

 colourless. It also makes many oils more limpid, and thus 

 renders them more active in the display of their peculiar pheno- 

 mena. Oil of turpentine alone gives a delicate film with iri- 

 descent rings and an outer border of minute globules, with 

 bosses within the edge : these flatten into discs surrounded by 

 small dots. Iridescent colours now set in and cover the film. 

 Suddenly the whole film opens into holes, which, in the midst of 

 the colours, have a beautiful effect. The film slowly disappears, 

 leaving an outline lace-pattern which lasts for hours. 



Now when oil of lavender is adulterated with turpentine in 

 the proportion of 5 to 1, the film spreads with a brilliant display 

 of colour, which is characteristic of the turpentine, the lavender 

 being colourless; at the same time the peculiar worm-eaten 

 pattern of lavender is more minute, and its action much more 

 rapid than in the case of the pure oil. By increasing the pro- 

 portion of the turpentine, the characteristics of the latter film 

 override those of the former. 



Now this brings me to speak of the use to which these cohe- 

 sion-figures may be applied in detecting adulteration. It is 

 perfectly easy to distinguish unwashed ether from rectified ether, 

 alcohol from spirits of wine, &c, by their respective cohesion- 

 figures. It is also equally easy to name a varnish, a fixed, or an 

 essential oil, from the characters of the film which a drop of 

 each substance forms on water. Having become acquainted 

 with the characters of each film, it is not difficult to detect the 

 films formed by mixtures, and even to name the component 

 parts of a mixture. For example, oil of cinnamon is now worth 

 about 5s per oz., so that there is an inducement to adulterate it. 

 The readiest means of adulteration is with oil of olives or oil of 

 sweet almonds. To be able to detect the adulteration, we must 

 become acquainted with the characters of the films of all three 

 oils. Now, to begin with oil of cinnamon : — As soon as a drop 

 of this substance is delivered to the surface of the water, it 

 spreads out into a film, but the more fluid portion of the oil (the 

 elceopten) precedes the film in radial lines of minute globules, 

 and these form an outer boundary line of detached spots to the 

 film. The film itself even on a large surface of water is not 

 more than about an inch in diameter ; it is of a beautiful delicate 

 structure and silvery reflection ; its edge is well defined, and it 

 has small bosses just within it. Almost immediately after its 



