42 Prof. J. Plateau on the Figures of Equilibrium 



mix glycerine with this solution in a proportion not much differ- 

 ent from that required when soap is employed. The solutions 

 thus prepared were ready for use by the next day, or the next 

 but one, and they yielded bubbles of 1 decimetre diameter, whose 

 maximum persistence in the air exceeded twenty-four hours. 

 Oleate of soda is therefore the substance with which the glyce- 

 rine solution ought properly to be prepared ; it is the substance 

 indicated by theory ; and the preparation by means of it becomes 

 a matter of the greatest ease. Unfortunately, pure oleate of 

 soda is not an article of commerce, and it can therefore be pro- 

 cured only by appealing to the kindness of a chemist. 



In a closed vessel, bubbles formed of the glycerine- solution 

 show a degree of persistence which is very much greater still, 

 especially if a substance like chloride of calcium, capable of ab- 

 sorbing moisture, is put at the bottom of the vessel. For ex- 

 ample, with a solution prepared with oleate of soda, but which 

 was not particularly good, and gave bubbles which did not last 

 more than twelve hours in the air, I obtained without drying the 

 air in the vessel a maximum persistence of forty-one hours, and, 

 when the air was dried, a persistence of more than fifty-four 

 hours. In the complete memoir I have pointed out some pre- 

 cautions that ought to be taken. 



I return from this discussion of the glycerine-solution to the 

 generation of films. In my Second and Sixth Series I have ex- 

 amined the generation and all the peculiarities (1) of the films 

 formed by filling up with oil a solid framework immersed in the 

 alcoholic liquid, and then gradually removing oil from it, (2) of 

 the films raised by air-bubbles on the surface of a liquid, and 

 (3) of those which start from the wires of a solid skeleton figure 

 which is immersed in the glycerine- solution and then lifted out. 

 In the present series I extend this examination to other kinds of 

 liquid films. 



I begin with complete bubbles obtained by blowing through 

 a tube widened out at the further end. When, for example, the 

 opening of the bowl of a tobacco-pipe is dipped into soap and 

 water or into the glycerine-solution and then withdrawn, a 

 small film extends at first from the liquid to the mouth of the 

 bowl; and I show that on continuing to raise the latter, the 

 equilibrium of the figure of the film soon becomes unstable ; the 

 film then contracts, closes up rapidly below, separates from the 

 liquid, and comes to fill the mouth of the pipe as a plane film. 

 In this state of things, on blowing down the stem of the pipe, 

 this film being now subject to an excess of pressure upon one 

 surface, must either burst or bulge outwards ; now, unless it is 

 exceedingly thin, its cohesion will be more than sufficient to 

 prevent it breaking; consequently it will begin to bulge and 



