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 fatly 
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 
could 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 developed (the bottle 
measured three and a quarter inches in diameter), which 
could evidently not have occurred had the liquid been 
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 ; for 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. I then increased the 
quantity of glycerine, so that the two substances were 
about equally divided, and even then bubbles two inches 
in diameter were obtained. 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- 
ties are analagous with those of the soapy solution, al- 
though less pronounced, I considered it useless to make 
the same experiments in reference to it. 
Now, if the cause which originates the formation of 
the effectual coating upon the saponaceous solution is 
due neither to the action of carbonic acid contained in 
the air, nor to the evaporation of water, whence 
does it arise ? Must we have recourse to Dupre’s some- 
what unacceptable idea, 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 than 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 Dupr6’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 DuprG, 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. DuprG 
concludes that in the stream of saponaceous solution, 
where the surface is constantly renewed, the soap itself 
has 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 does 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- 
gom’s needle when in the 1 quid and when removed from 
it were respectively five 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 nearly 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 attributing it to the principal one of them. 
Finally, the resistance in regard to the displacing of 
molecules cannot be denied as far as the superficial layer 
of saponaceous solutions is concerned, consequently 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 of 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- 
self to one of them as follows : 
A bubble about an inch and a half in diameter is blown 
and placed 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- 
j creasing its dimensions until it bursts. The spray imme- 
| diately spreads itself upon the liquid in several parts, each, 
! however, being separated from the surface. by a small 
quantity of air, and gradually disappears as though 
sinking into the mass, the contraction occupying several 
seconds. 1 
M. Marangoni, although maintaining perfect silence in 
1 In order to make this experiment successful, it i ; necessary to use a 
perfectly pure solution. 
