ON THE VERIFICATION OF CASTOR OIL. 
391 
may in their turn have to depend upon others. So that the production of an 
undoubted specimen is not always easy, unless prepared at home, which is also 
not always easy. At the International Exhibition I often watched the process 
of crushing linseed and expressing the oil; and I obtained specimens of the pro¬ 
duct, including the seeds. Now, thought I, I have an undoubted specimen of 
linseed oil; but on examining the seeds they were found to be mixed with about 
one-fiftli of other seeds, so that my specimen of linseed oil from this source 
could not be relied on. Other circumstances may modify the cohesion figure, 
such as differences in the climate, or in the season under which a crop is gathered. 
Thus, oil of lavender varies somewhat in specific gravity in different years from 
the same farm, and I have observed that the beautiful carrageen-moss pattern 
produced by this oil is more minute in some specimens than in others ; but the 
pattern is still the same, in the sense that the Queen’s head is the same, whether 
seen on a sovereign or on a half-sovereign. 
In general, when there is an admixture of oils the characters of the two 
figures appear at once. Thus, olive oil has its cohesion figure ; oil of sesame, 
with which it is often mixed, has quite another figure ; a mixture of the two 
in various proportions will give a figure which is neither that of olive oil nor of 
sesame, but giving the characters of both, leaning of course to the side of that 
which is in excess. In some cases, however, the characters of the added oil do 
not at once appear, and this is the case when lard oil is added to castor. The 
figure opens in the same beautiful manner, and goes through its lovely phases, 
with a difference, it is certain, that requires a practised eye to detect; but there 
is no difficulty in detecting the lard oil among the residual phenomena of the 
experiment. Outside and beyond the castor-oil figure, we have numerous small 
blotches of lard oil, which are entirely absent from the residual phenomena of 
the pure castor-oil figure. I have selected lard oil as being the most common 
source of admixture; I suppose as much as ten per cent, might be added with¬ 
out greatly reducing the viscidity of castor oil. Doubtless any large admix¬ 
ture, if it were worth while, of olive, nut, etc., oils, would be at once seen by 
the increased fluidity of the castor oil; but I do not imagine any difficulty in 
detecting these oils in the mixture, their nature, and even amount (roughly) by 
means of their cohesion figures. 
I do not give diagrams of the figures produced by these various admixtures. 
The subject requires an education of the eye, which is soon completed, as far 
as the figures are concerned, for any one who works at the subject; and no one 
can work at a subject long without getting that technical kind of familiarity 
which no books or graphic illustration can supply. 
Croton oil furnishes a magnificent cohesion-figure which may be represented 
as a very enlarged pattern of that of castor oil. Whether a small admixture of 
croton oil, such as one per cent, with castor oil, could be detected by means of 
the resulting figure, I am not yet prepared to say. I think there is no difficulty 
in detecting five per cent. 
Oil of turpentine forms a very characteristic figure. It flashes out on the 
surface of water into a large well-defined film, the edge is marked by a double 
row of small bosses, the outer being the smaller; in the course of a few minutes 
irregular patches of iridescent colour appear on the surface, the film then be¬ 
comes perforated by a multitude of minute holes, and the fourth and final stage 
is an exceedingly delicate resinous network, which is very permanent. Oil of 
turpentine is, I am told, sometimes mixed with castor oil as a vermifuge. It is 
perfectly easy to detect the admixture by means of the cohesion figure. 
I fear I have left myself but very little time for any remarks on balsam of 
copaiba. The readiness with which this substance unites with the oils, both 
fixed and volatile, renders an easy and reliable test desirable. A drop of the 
pure balsam spreading out with its cohesion figure on the surface of water is a 
magnificent sight. It consists of a succession of sharply cut, expanding, super- 
