406 Transactions.—Chemistry. 
sary as a property of the Milanos floating thereon ; for it seems to be 
certain that all the substances here cited which describe movements upon 
water, with the exception of camphor, form solutions or compounds with 
water possessing more viscidity than water does. As regards camphor, we 
can get no positive evidence that the substance it forms upon water is thus 
more viscid than water, as we cannot collect it in sufficient quantities for 
the examination necessary ; but we may safely assume, from analogy, that 
it is viscid, and highly so. I think it may be taken as a fact that any solid, 
which, when placed upon water, has a greater tendency to spread upon its 
surface than to combine with the bulk of it (as camphor, citric acid, ete., do), 
will form a compound therewith of a nature more viscous than water. 
I suppose the solution thus radiating from a solid along the water surface 
to be saturated, as in such a condition its viscosity will be greatest. I need 
not demonstrate to you that a substance which forms with water a com- 
pound more viscid than water, should spread largely when placed in contact 
with the surface of water; it is a mere physical matter, one of least re- 
sistance; such substances encounter but little more than half the resistance 
to movement when extending along the surface than when penetrating the 
liquid underneath ; the movement in the former case is, too, far more rapid 
than that in the latter; but as capillary attraction is probably concerned as 
an accelerator of such movement, I cannot well claim that this superior 
rapidity is a measure of the greater ease with which the viscid product ex- 
tends itself over the surface than it does internally. 
And now with special regard to the cause of camphor movement: it will 
occur to you that if the compound which camphor forms with water is so 
highly viscid as I here maintain, the movements in question may have their 
stimuli in part due to an effect springing out of this viscidity ; it would seem 
that,—as there is a constant production of this viscid substance close to 
the camphor, and a little above the water-line, as well as on it,—this sub- 
stance exercises a slight pressure on the camphor in virtue of its viscidity, 
and the camphor, therefore, is urged wherever the solution is less viscid. I 
conceive this supposition to be a correct one, and, therefore, that in addition 
to the motive power capable of being derived from the effect of superficial 
affinities and adhesions, as cited in my former paper upon this subject, there 
is that derivable from an unequal solution of the substance operated with 
in a menstruum of unequal viscosity. 
