392 
PHARMACEUTICAL MEETING. 
posed disks, glowing with the most brilliant iridescent colours, of a lustre all 
but metallic. These disappear when the adhesion of the surface is satisfied, and 
a clean, sharply defined, colourless disk is left on the surface. 
Now I am told that balsam of copaiba is often mixed with castor oil in 
various proportions, to the great embarrassment of the medical practitioner. He 
is taught by the older Pharmacopoeias to shake up the balsam with alcohol; but 
as castor oil is also soluble in alcohol, the test is worthless. The magnesia test is 
troublesome, and a drop on writing-paper almost equally so ; but a drop on the 
surface of water, so far as I have examined it, instantly detects the admixture. 
The castor-oil figure has narrow iridescent rings, and a wide and beautiful lace- 
border ; the balsam figure has wide rings, a clean cut edge, and no border ; but 
curiously enough, the mixture of the balsam with the castor oil gives a figure 
with no colour, and a scanty perforated border. 
I have not tried this experiment with various proportions of castor oil. In¬ 
deed, my object to-night is not to lay before you a finished work, but rather to 
invite attention to the subject, and to court inquiry and examination. When I 
brought this subject before the British Association at Manchester two years and 
a half ago, my object was rather scientific than practical. I wished to establish 
the principle that cohesion asserts itself in the case of liquids in the production 
of definite figures, as it does in the case of solids in building up crystals. The 
principle has, I believe, been admitted ; but I have made no great progress in its 
practical application, partly from the difficulty I have had in procuring pure 
specimens, and partly, I suppose, from my preference for scientific inquiry, 
rather than practical application. 
In conclusion, I must thank Professor Bentley for a very good specimen of 
wood oil, which I believe has been imported as East India copaiba. It makes 
a very good figure, a sort of inferior copaiba figure on a small scale ; but it 
cannot for a moment be mistaken for copaiba, or any other figure that I am ac¬ 
quainted with. I have not tried the effect of it when mixed with copaiba, nor 
have I had an opportunity of examining jatropa oil, which is sometimes mixed 
with copaiba. There can be no difficulty in detecting admixtures of turpentine 
by this method. 
I must also take the opportunity of Professor Miller’s presence here to-night, 
to thank him for the warm interest which he has taken in this subject from the 
first. He witnessed my earliest experiments, and it is owing to his encourage¬ 
ment and advice that I have been induced from time to time to push on with 
the inquiry. 
Professor Miller, of King’s College, said he felt great interest in the subject 
Mr. Tomlinson had brought before the meeting. He had had many op¬ 
portunities of witnessing Air. Tomlinson’s experiments during the progress of 
his investigations. He had observed that there was one practical difficulty in 
arriving at precision in the application of this method of testing, which arose 
from the absolute necessit} r of having the glass containing the water chemi¬ 
cally clean. It was very important to attend to this point, as an experiment 
would probably fail altogether from the absence of perfect cleanliness. 
IRinsing the glass with solution of potash, would be found the best means of 
bringing it into the required condition. 
Dr. Attfield thought they were scarcely in a position to discuss the merits 
of the paper or to comply with the invitation of the author to express an opi¬ 
nion upon its practical value, as the subject was entirely new to them. He 
should like to know whether Mr. Tomlinson could lead them to expect that by 
taking advantage of the varying cohesive and adhesive powers in different 
liquids which might be used as beds on which to place the drops of oil, a co¬ 
hesion figure might be obtained which would be characteristic of a given oil. 
and identify it in the presence of others. 
