New Experiments with Soap Bubbles. 359 



bubble by bursting resolves itself into the simpler form of 

 spray. Besides this, as will subsequently be shown, the film is 

 of excessive tenuity, and the rapid evaporation of liquid from 

 its comparatively enormous surface, soon reduces its thickness 

 to the bursting point. In fact, a soap bubble depends for its ' 

 being on the accurate adjustment of the equilibrium of many 

 component forces, each of which acting alone would be 

 its destruction, and this equihbrium, being but unstable, is 

 destroyed by the slightest cause. But, on the other hand, if 

 these conditions of its existence be not interfered with, a soap 

 bubble will bear an amount of rough treatment that is sur- 

 prising in a being otherwise so ephemeral. 



Thus our bubble, though a charming thing while it lasts, 

 has such a fragile nature that it can with only the greatest 

 difficulty be employed for any long-continued observation • 

 and for this reason many attempts have been made to discover 

 some means of prolonging its existence. For though gene- 

 rally only considered as a toy, it has already been found to have 

 its uses. Newton spent much time in endeavouring to dis- 

 cover the cause that produced its glorious tints, and how well 

 he succeeded is known to most of my readers. Faraday made 

 soap bubbles the vessels for containing the gases between the 

 poles of the electro-magnet in his great experiments on the 

 magnetism of gases. As a means of prolonging the existence 

 of the bubble, Brewster* recommends the addition of some 

 sugar to the solution, which, by somewhat diminishing the 

 fluidity, has some effect, and makes it slightly more available 

 for optical purposes. But the successful method is that em- 

 ployed by M. Plateau, the Belgian physicist, who, finding a 

 liquid film necessary to his researches on the deportment of 

 liquids freed from the influence of gravity, invented a solution 

 which forms bubbles of a beauty and permanence almost 

 incredible. The recipe for this solution in its most perfect 

 form is as follows : — - 



Dissolve one part of pure oleate of soda in fifty parts of 

 distilled water, and to every three volumes of the clear solution 

 thus formed, mix two volumes of pure glycerine. 



This mixture, used instead of soap and water, with a 

 common tobacco-pipe, gives bubbles whose tints 

 are truly gorgeous, and which are best observed 

 in the following manner : — Take a piece of iron 

 wire, about the thickness of a darning needle, 

 and after cleaning off any rust with sand-paper, 

 bend it in the form here given, the diameter of 

 the ring being about If- inches. This is readily 

 managed by wrapping it round any convenient 

 * Optics. Ed. 1853, p. 119. 



