certain Vapours on Films, fyc. 117 



creosote; the cohesion of the creosote tends to prevent this 

 action, and the struggle between the two is manifested by a 

 series of vibrations which take place at the edge of the disc ; 

 the creosote tends to spread, its cohesive force struggles to pre- 

 vent the spreading. Small globules, however, are constantly- 

 being torn away from the parent drop, and as these spin round 

 and disappear, they leave a film which gradually covers more or 

 less of the surface of the water. The motions of the parent 

 disc and of the globules cease; but as the film becomes dissolved 

 by the water, the motions (now very slow ones) set in again with 

 the formation of another film, which in its turn is dissolved. 

 But if the quantity of water be small, the globules soon cease to 

 be disturbed, since the water has become saturated, or the adhe- 

 sion of the water balances the cohesion of the globule, and hence 

 the quiescence. 



When I showed you this experiment, it naturally struck you 

 as a case of solution, and you inquired whether the motions of 

 the disc would take place in a saturated solution. I had already 

 ascertained that if, when one drop, or rather disc of creosote, 

 is in rapid agitation, and also moving about on the water, a 

 second drop be placed by its side, it stops the motions of the 

 first disc, and is itself soon brought to rest. In other words, 

 the water is sooner saturated. 1 further ascertained that if, 

 when the discs of creosote are at rest in a small quantity of 

 water — a wine-glass full, for example — the contents of such 

 wine-glass were transferred to a half-pint goblet nearly full of 

 water (the transfer being gently made, so as to keep the creo- 

 sote on the surface), the motions of the discs will begin again 

 with as much energy as before. When this half-pint of water 

 is saturated and all motion has ceased, the motions will be re- 

 newed if the half-pint of water be poured into a large soda- 

 water glass, two-thirds filled with water. 



Thus, by increasing the quantity of water, we remove it 

 further from the point of saturation, and favour the gyrations 

 and other motions of the creosote. The same effect may be 

 produced if (the quantity of water being fixed) we increase its 

 solvent power. For example, a disc of creosote is very lively 

 for some minutes on the surface of water; but as the latter be- 

 comes saturated the motions decline, and then cease. If we 

 now touch the water with a glass rod wet with acetic acid, a 

 new solvent power is conferred on the water, and the motions of 

 the creosote set in again. So also these and other motions may 

 be produced if we hold over the quiescent globule the vapours 

 of substances in which creosote is soluble. The cthcr-sponge 

 will cause the disc to display its crispations, and to dart out 

 The ammonia sponge restores motion to 



