Liquids on the Surface of Water, 39 



No effect, probably because the vapour of the disulphide being 

 heavier than that of the oil prevents it from being deposited on 

 the surface of A, and so renders any variation in tension impos- 

 sible. When, however, the vapour of the disulphide acts on a 

 surface of turpentine dusted over with lycopodium, the particles 

 near the end of the tube move up to it and produce a centripetal 

 current. 



18. I will now give some further experiments of my own, 

 illustrating on a large scale the formation of centrifugal and 

 centripetal currents. A bit of sponge tied over the end of a 

 glass rod (1 a) was used to convey the vapour, a separate sponge 

 being used for each liquid. 



Vapour of chloroform produces powerful centripetal currents 

 in the films of various oils &c. on the surface of water. Many 

 years ago I observed that a large film of black Japan varnish on 

 the surface of water contained in a dinner-plate was singularly 

 acted on by the chloroform-sponge. The vapour first converted 

 it into a multitude of minute globules, which then moved up to 

 the sponge as to a common centre of attraction. 



A similar effect is produced by the action of the ammonia- 

 sponge on a film of oil of tar ( 01. picis) . No sooner is the sponge 

 held over the film than it separates into distinct portions, and 

 each portion gathers itself up into a very convex lens, which re- 

 flecting the light, the appearance is as if the surface were all at 

 once studded with eyes. The effect is very singular and striking. 

 Chloroform slightly repels this film. 



Oil-of -turpentine Film. — Chloroform powerfully attracts and 

 gathers it together. Tt does the same with films of the oils of 

 origanum, rosemary, lavender, and many others. But it often 

 happens that, when chloroform has gathered up the film, the 

 ammonia-sponge will spread it out sufficiently thin to form iri- 

 descent colours. Such is the case with the films of oils of laven- 

 der, amber, &c. So also benzole will thicken and attract a film, 

 while ether will scatter and repel it. The naphtha-sponge acts 

 centripetally on the oil-of-sassafras film, while on a film of oil of 

 pepper it produces a remarkable swinging to-and-fro motion. 

 Acetic acid, in which oil of lavender is soluble, acts by its vapour 

 upon a film of the oil in a very marked manner, attracting it and 

 gathering it up into little disks. This film is also very sensitive 

 to the ether-sponge, even when held at a great distance above. 

 The oil-of-aniseed film is dispersed by ether and brought together 

 by ammonia. A film of oil of turpentine is first repelled and 

 then attracted by the ammonia-sponge. The oil-of-rosemary 

 film is gathered up by the vapour of carbonic disulphide. Ether 

 disperses a film of oil of peppermint ; vapour of turpentine brings 

 it together. 



