454 On Figures of Equilibrium of a Liquid Mass without Weight, 



In the third place, among the liquids of the second Table, 

 the one which shows the smallest ratio is solution of resin-soap, 

 and this is also the liquid in which bubbles attain the smallest size. 



The small difference will no doubt be observed between the 

 ratios 10*65 and 11*05, belonging respectively to solution of car- 

 bonate of sodium, which does not admit of being blown into 

 bubbles, and to solution of resin-soap which does yield bubbles 

 up to a certain diameter. But this, again, is a consequence of 

 our theory ; in fact, according to our Tables, the superficial vis- 

 cosity is smaller in the second of these liquids than in the first, 

 and, as I have stated above, the ratio at which the formation of 

 bubbles first becomes possible is higher the greater the super- 

 ficial viscosity. It is therefore intelligible that, if the ratio 11*05 

 for resin-soap allows of the formation of bubbles of moderate 

 size, this same ratio (and still less the somewhat smaller ratio 

 10*65) will not allow of the formation of bubbles in solution of 

 carbonate of sodium. 



Lastly, my theory leads me to a complete explanation of the 

 long persistence of bubbles blown with the glycerine-solution, 

 as well as of the singular property possessed by the film which 

 forms them of not diminishing in thickness beyond a certain 

 degree, and then increasing in thickness again. In the first 

 place, I endeavour to find the approximate value of the superficial 

 viscosity of the liquid in question, and I find it equal to 80*25, 

 whence it will be seen that it is distinctly less than that of water j 

 the tension of the films is the same as for solution of soap, 

 namely 5*64; hence for the ratio of these two elements in the 

 glycerine-solution we have the number 14*22. Bearing in mind 

 the comparatively low value of the superficial viscosity of the 

 glycerine-solution, this ratio may be looked upon as high, and 

 is much greater than is needful for the formation of bubbles j 

 accordingly the glycerine-solution yields very large bubbles. 



But this liquid absorbs moisture from the air, and consequently, 

 when a bubble has been blown with it, the film is subject to two 

 opposite influences — namely, that of weight which tends to make 

 it thinner, and that of absorption, which tends to thicken it. 

 The former predominatesat first, and the film gets thinner; but 

 the descent of the liquid becomes slower through two causes — 

 first, the diminution of the mass, and, secondly, the gradual ab- 

 sorption of moisture, which renders the liquid more aqueous and 

 thus approximates its viscosity to that of water. It follows that 

 soon the descent of the liquid becomes so slow that the augmen- 

 tation of thickness due to absorption predominates. As regards 

 the tension, M. Dupre has found that in solution of soap it 

 varies extremely little with the proportion of water ; and this 

 probably holds good for the glycerine-solution also. 



