388 
PHARMACEUTICAL MEETING. 
The cultivation of castor oil is said to be increasing in France; the yield is 
very great, a single plant from one seed producing upwards of 800 or 900 seeds. 
The seeds sometimes yield more than half their weight of oil. The French and 
Italian oils are weaker than those from the tropics. Italian oil, prepared in 
Italy, of which there are some samples on the table, is a good bland oil. There 
are also other specimens, prepared in this country from decorticated Italian 
seeds. 
The oil, as you know, is very viscid, the colour is yellowish, the taste, or 
rather after-taste , somewhat acrid, varying however with the freshness of the 
oil, and the mode of preparation. It retains its fluid, viscid character probably 
as low as 0°F. It differs from other fixed oils in being soluble in alcohol, a pro¬ 
perty which was long regarded as a test, until Pereira pointed out the fact that 
castor oil enables other fixed oils to dissolve in alcohol to the extent of 30 per 
cent, and upwards, so that a specimen may be mixed with olive, lard, nut, and 
other oils, and yet be soluble in alcohol. For example, one volume of olive oil, 
two volumes of castor oil, and two of rectified spirit, shaken together and gently 
heated, will form a transparent homogeneous solution. Benzoic acid and cam¬ 
phor also increase the solubility of castor oil in spirits containing 75 per cent, of 
alcohol (sp. gr. O'860). What is called concentrated castor oil is common castor 
oil mixed with a small proportion of croton oil, which also enables other fixed 
oils to dissolve in alcohol to the extent of from 30 to 50 per cent. 
It is superfluous to remark in this place that the distinction between chemistry 
and physics is not recognized by nature. Hence a lecturer on physics may ad¬ 
dress chemists without being accused of temerity, and there are numerous pre¬ 
cedents for substituting a physical test for a chemical one, where the latter is 
defective, or not sufficiently expeditious for ordinary purposes. Such is the test 
that I venture to propose to-night, and I apply it to castor oil and balsam of co¬ 
paiba, not because it is peculiarly adapted to those substances, but because they 
are so well known and so largely used in medical practice. My test is of a far 
more general kind. It is applicable to every independent liquid, by which I 
mean, not a solution, although it is possible that hereafter solutions may be ex¬ 
amined by its means. The test, as I now submit it to your critical judgment, 
depends on the forces of cohesion, adhesion, and diffusion. For example, if I 
gently deposit a drop of an oil hanging from the end of a glass rod, upon the 
surface of chemically clean water, contained in a chemically clean glass, a con¬ 
test takes place between the forces in question the moment the drop flattens 
down by its gravity upon the surface of the water. The adhesion of the liquid 
surface tends to spread out the drop into a film, the cohesive force of the parti¬ 
cles of the drop strives to prevent that extension, and the resultant of these two 
forces is a figure which I believe to be definite for every independent liquid.* 
The figure thus produced I name the cohesion figure of the liquid in question. 
Doubtless if there be two or more liquids in nature of different chemical compo¬ 
sition, but precisely alike in their physical characters, such as their density and 
molecular attraction, and relations to heat, whereby at a given temperature they 
are equally fluid, or limpid, or viscid, then doubtless the cohesion figures of 
those two liquids would be identical. I have succeeded in converting the cohe- 
* Strictly, the figure is a function of adhesion, cohesion, and diffusion: or—• 
F =/( CAS) 
in which F is the figure, C the cohesive, A the adhesive, and 5 the diffusive forces. The formula 
may also be represented in other ways. For if S be the solubility, d the density, and a the 
molecular attraction, then— 
F =/(S 5) 
or F = f(Sda) 
or F = f (CAda) 
all these being identical. 
