288 M. J. Plateau on the Figures of Equilibrium 



out in a note at the end of the memoir, the proper way to obtain 

 sufficiently good results with the ordinary glycerine of com- 

 merce. 



The mixture must be prepared in summer, and when the tem- 

 perature out-of-doors is at least 19° Cent. Dissolve at a gentle 

 heat one part by weight of Marseilles soap, previously cut into 

 thin shavings, in 40 parts of distilled water ; and when the solu- 

 tion is cold, filter it. That done, carefully mix in a flask by 

 violent and continual agitation, 2 vols, of glycerine with 3 vols, 

 of the above-mentioned solution, and then allow it to stand. The 

 mixture, limpid at the time of its formation, begins aftersome hours 

 to grow turbid } a slight white precipitate is produced, which rises 

 with great slowness, and after some days forms a distinct layer 

 at the top of the liquid ; the limpid portion is then collected by 

 means of a siphon, which draws off by a lateral tube, and the 

 preparation is at an end. 



The liquid thus obtained, and which I name glyceric liquid, 

 gives films of great durability ; for instance, if with this liquid, 

 by means of a common clay pipe, a bubble 1 decimetre in 

 diameter be inflated, and then placed in the open air of a room 

 upon a ring of iron wire 4 centimetres in diameter and 

 previously moistened with the same liquid, this bubble, provided 

 it is perfectly at rest, will remain entire for three hours. 



The glyceric liquid can be preserved about a year, after which 

 time it rapidly decomposes. I have not observed any disen- 

 gagement of gas ; however, as the liquid is of an organic nature, 

 it would not be unlikely that such might be produced sometimes ; 

 and it would be prudent, to prevent a possible explosion, to 

 only close the flask with a cork which does not fit very 

 firmly. 



Just as the films of soapy water last very much longer in a 

 closed vessel than in the open air, the endurance of the films of 

 glyceric liquid, already so great in the open air, becomes still 

 much more considerable when these films are enclosed in a vessel, 

 especially if certain precautions are taken. I shall quote an 

 example of this further on. 



Having thus obtained a liquid easily furnishing films both 

 large and very durable, I employ it in order to produce by means 

 of them all the figures, in a state of equilibrium, of revolution. In 

 order not to give this analysis too great length, I shall limit myself 

 here to succinctly describing the formation of the cylinder. 



For this purpose, use is made of an apparatus of two rings of 

 iron wire 7 centimetres in diameter, similar to those men- 

 tioned by me in the preceding series, that is to say, the lower 

 ring on a tripod, and the upper ring, supported by a fork, fixed 

 into the two extremities of its diameter ; the end of this fork is 

 attached to a support, fixed in such a manner that the ring can 



