300 



SCIENCE. 



liquids are never complete hemispheres. M. Marangoni 

 thinks it probable, as I have said before, that the coating 

 of dirt on the saponaceous solution is due to the action ot 

 carbonic acid contained in the air. 



I have ascertained that carbonic acid actually decom- 

 poses the solution inasmuch as it removes all fatty 

 acids ; but does the formation of the layer really arise 

 from this cause ? In order to discover this the following 

 experiment has been made : 



A certain amount of a concentrated solution of caustic 

 potash was placed within a bottle holding almost a 

 quart, then, after tightly corking the latter it was violently 

 shaken so that the liquid swept over every part of the in- 

 terior. The greater portion of the liquid was then 

 poured out and the bottle instantly re-corked. In the 

 meanwhile a funnel provided with a plug was procured 

 and the interior of its neck moistened with the solution 

 of potash ; it was then placed in the neck of the bottle 

 and wax applied at the junction. This done, almost 

 300 grammes of a solution of Marseilles soap pre- 

 viously rendered clear by means of filtration was poured 

 into the funnel and left there for one hour. At the end 

 of that time the wax was removed and the funnel gradu- 

 ally lifted, the plug being opened simultaneously, and, 

 as the liquid flowed into the bottle the funnel continued 

 to be slowly raised until the extremity of the neck was 

 about on a line with the top of the bottle ; the latter was 

 then rapidly corked, some of the liquid remaining in the 

 funnel. 



The potash necessarily absorbed the small quantity of 

 carbonic acid contained in the bottle, and at the moment 

 when the funnel was removed no exterior volume of air 

 CDuld possibly penetrate within the bottle, because the 

 stream of liquid flowing in must have expelled much more 

 air than could possibly have found its way in to re- 

 place the neck of the funnel. Finally, as merely a portion 

 of the liquid escaped into the bottle, and that at a distance 

 far above the free surface, it could absorb nothing from 

 the superficial layer. Now, with this liquid merely united 

 with air deprived of carbonic acid, transverse waves of a 

 very persistent character were easily d-veloped (the bottle 

 measured three and a quarter inches in diameter), which 

 could evidently not have occurred had the liquid b-en 

 without an efficient coating. It is quite impossible, there- 

 fore, for me to accept M. Marangoni's explanation. Be- 

 sides, the effectual coating upon the saponaceous solution 

 does not arise from the evaporation of water; lor a fatty 

 liquid like soap-suds, for instance, which produces bub- 

 bles in consequence of this consistency, does not evapor- 

 ate at all, but, on the contrary, attracts the dampness in 

 the air. In order to assure myself that the effectual coat- 

 ing of the saponaceous solution does not proceed from the 

 evaporation of water as M. Marangoni thinks it does, I 

 added two parts of Price's glycerine to three parts of the 

 solution, about the proportions generally used to produce 

 a liquid glycerine, and the two substances were thoroughly 

 mixed together. This compound, in consequence of the 

 glycerine, should absorb moisture instead of losing it ; 

 now, by means of a pipe it produced bubbles at least two 

 inches and a half in diameter. 1 then increased the 

 quantity of glycerine, so that the two substancts were 

 about equally divided, and even then bubbles two inches 

 in diameter were obtain d. Thus, the effectual coating 

 of the solution is not due to the loss of water by evapora- 

 tion. 



As to the solution of albumen, inasmuch as its proper- 

 ire analagOUS with those of the soapy solution, al- 

 though less pronounced, I considered it useless to make 

 ■ ■ p< rimi nts in reference to it. 



Now, if the cause which originates the Formation of 



ial (oiling upon tin,- saponaceous solutionis 



due nei hei to the action of carbonic acid contained in 



nOl tO I on Of water, u I 



Musi vv( h 1 I >upr£'s some- 



what unac eptable ide l, which holds that in certain solu- 



tions the substance dissolved rises abundantly to the 

 surface ? Is it not much easier to admit, as I do, that 

 the superficial coating of liquids forms itself sponta- 

 neously into a particular condition, which results in a 

 greater or less difficulty in regard to the relative dis- 

 placement of the molecules thau could occur in the inte- 

 rior of the mass ? Does not the fact that tension exists 

 suffice to show that this coating possesses an especial 

 character in reference to the action of molecules ? 



The experiment which originated Dupre's singular 

 idea mentioned above, is based upon the fact that the 

 height of a fine stream of liquid precipitated from a cer- 

 tain distance must be considerably diminished by the 

 tension of its surface, and Dupre, therefore, concludes 

 that in a little stream of soap-suds the tension is sensibly 

 identical with that of pure water, while we all know that 

 when a solution of soap is in a state of repose its tension 

 does not approach that of water by two-thirds. Dupre 

 concludes that in the stream of saponaceous solution, 

 where the surface is constantly renewed, the soap itself 

 his no opportunity of coming to the outside. But in 

 my theory — a remarkable fact which I have myself con- 

 firmed by an entirely different process which it is useless 

 to refer to here — proves that the superficial coating of 

 liquids requires a certain amount of time, however short, 

 to assume its proper atomical condition. 



"But," says M. Marangoni, "the superficial coating 

 of the saponaceous solution has no extraordinary visci- 

 dity ; on the contrary, it is very susceptible of motion." 

 I acknowledge that it docs in fact possess great mobility, 

 which proceeds from the extreme thinness of its consist- 

 ency. Also, it is capable in itself of making but slight 

 resistance towards the movements of the magnetized 

 needle. Still, as it adheres in its fullest capacity to the 

 underlying liquid, and should therefore attract a certain 

 amount of the latter as it rotates, a greater part of the 

 resistance must necessarily be due to this fact. More- 

 over, we observe, nothing goes to show us that the su- 

 perficial layer, although very mobile, is less so than the 

 underlying liquid if both are of an equal consistency. 

 We can reasonably admit this after an experiment with 

 the magnetized needle placed within the liquid. Indeed, 

 as the number of oscillations performed by M. Maran- 

 goni's needle when in the 1 quid and when removed from 

 it were respectively rive to six, the governing powers of 

 the needle in these two conditions are in proportion to 

 the square of the above numbers, as, for instance, thirty- 

 six to twenty-five, or about three to two. The resistance 

 of the liquid robs the needle of neirly one-third of its 

 governing force; only as we require which part the two 

 superficial coatings play in this resistance, nothing pre- 

 vents us from a'tributing it to the principal one of them. 



Finally, the resistance in regaid to the displacing of 

 molecules cannot be denied as far as the superficial layer 

 of saponaceous solutions is concerned, const quently we 

 should admit this fact, although in a much less degree, 

 in reference to solutions of soap itself. In one of my 

 papers, and also in paragraph two hundred and seventy- 

 eight ol my book, I have described a certain number of 

 facts which prove the rigidity existing in the effectual 

 elevating of the saponaceous solution. 1 will confine my- 

 s; II to one of them as follows : 



A bubble about an inch and a half in diameter is blown 

 and place I upon the surface of the liquid ; now, holding 

 the mouth of the pipe in close contact with the hemisphere 

 into which the bubble is transformed, you blow gently, in- 

 creasing its dimensions until it bursts. The spray imme- 

 diate! itself upon the liquid in several parts, each, 

 however, being separated from the surf. ice by a small 

 quantity of an. and gradually disappears as though 

 sinking into the mass, the contraction occupying several 



second .' 



M, Marangoni, although maintaining perfect silence in 



'In ei' 1 1 mal this experiment successful, it 11 necessary to use a 

 ition. 



