ON THE VERIFICATION OF CASTOR OIL. 
3S9 
sion figure of one essential oil into that of another by dissolving camphor in one 
of them, but in such case other characters were introduced which disturbed the 
comparison. 
As the cohesion figure of a liquid depends so much on the adhesion of the 
surface, it is quite necessary that that surface be chemically clean. The water 
need not be distilled. I have found the New River Company’s water well 
adapted to the purpose, but the vessel must be specially prepared. All vessels 
exposed to the air contract an organic film from their condensing on their sur¬ 
faces the breath of animals, etc., and also other impurities from the products of 
combustion, dust, etc. If we attempt to clean the glass with a duster, however 
well we may satisfy the eye, we do not remove this organic film, or if we remove 
one, we substitute another from the cloth held in the hands ; so that when the 
glass is filled with water, the film in question is detached, and spread over the 
liquid surface, effectually preventing adhesion. The plan I recommend is to ap¬ 
propriate certain glasses, about four inches in diameter at the mouth, to the pur¬ 
pose ; to wash them out occasionally with commercial sulphuric acid, to rinse 
with water, and after every experiment to wash out the glass with a solution of 
caustic potash, and to rinse with water before filling up again. The water used 
for the experiment must be allowed to come to rest before the drop is deposited. 
The glass rods kept for the purpose should be of the same size, and these may for 
convenience be kept in the caustic potash vessel. When one is taken out, it 
should be shaken in water and wiped dry on a clean cloth. On dipping it into 
the oil, etc., it may be stirred round to mix the layers, if any, and then allowed 
to drain until the drops fall slowly ; and the eye must determine when the rod is 
to be carried over the water, so as to deposit one, and only one drop, neatly and 
gently without any disturbance. In this, as in all other matters, doubtless each 
operator will have his personal equation, so that one man’s result may not be 
precisely the same as that of another ; but if the foregoing directions be attended 
to, sufficiently good cohesion-figures will be produced. Gentlemen have come to 
me, and have complained of their inability to get consistent figures ; but on in¬ 
quiry I have found their glasses not clean, or the mode of depositing the drop 
unsteady. In one case I saw a gentleman drop the liquid from a height of ten 
or twelve inches. I may also remark that in the case of fixed oils, it is of no use 
placing a second drop after the first one has failed, for in such case, the second 
drop either simply flattens, or in the case of some essential oils presents a beauti¬ 
ful example of the spheroidal condition of liquids at ordinary temperatures. 
With some other volatile oils a second drop will displace the film formed by 
the first and produce a second cohesion figure on the same surface. With 
respect to the ethers, alcohol, etc., it is different: each drop forms a sharp 
and well-defined figure, lasting only about a second, and hence the best way of 
exhibiting such figures is to have the liquid in a dropping-tube, and allow drops 
to fall in regular succession on the surface of the water, by which means a regu¬ 
lar succession of figures may be kept up and their characters studied. Here is 
some of Mr. Morson’s creosote. A drop placed on the surface of two ounces of 
water forms a highly characteristic figure, sailing about with a vibratory, cris- 
pating edge. In the course of seven minutes this drop becomes gradually dis¬ 
posed of by solution ; or in other words, the adhesion of the water completely 
overcomes the cohesion of the liquid, and diffusion spreads it through the mass 
of the liquid. A second drop may now be placed on the same surface. It ex¬ 
hibits the character of the first figure in a mitigated form ; it is less active ; it is 
disposed of by solution in 121 minutes ; a third drop is disposed of in 25 mi¬ 
nutes ; a fourth drop ceases to give a cohesion figure at all: it is not disposed of 
after 110 minutes. In fact, the two ounces of water are saturated: that is, the 
adhesive force of the water and the diffusibility of the creosote are destroyed. 
Increase the quantity of water, and we restore the adhesive force and diffusibility 
