ON THE COHESION FIGURES OF LIQUIDS. 
497 
was large, the bosses at the edge larger and flatter than in the two former 
specimens, and not so well defined. A fourth was a specimen of the essential 
oil of copaiba. It opened with a sudden flash of coloured rings, forming a 
colourless disk over the whole surface with no bosses at the edge. 
On thinning down the second specimen with oil of turpentine a colourless 
film was produced similar to that of the third. 
The second specimen was also mixed with f, and nearly f- castor oil, (No 
1 castor oil in my twelve specimens being used), and in all cases a film en¬ 
tirely devoid of colour was produced. The splendid iridescent disks of the 
balsam, and the rainbow-rings of the castor were entirely absent in the mix¬ 
ture of the two, in consequence of the increased thickness of the resulting 
film. The mixtures were made in a test-tube held in warm water, and stirred 
with a glass rod. 
Fig. 2 is a portion of the figure of a sample of croton oil, of a brownish- 
amber colour: this opened into splendid rings, which quickly disappeared, 
when the film retreated upon itself, leaving a minute spray of oil. Another 
specimen which I have had by me about two jmars, opened with a fine dis¬ 
play of rings, and a corona which formed a large perforated pattern, when the 
film gathered itself up, and left a trail of oil behind. The figure was like that 
of the first, only in the gathering up, the edge of the film was torn away. A 
specimen from the Dutch Court of the International Exhibition, probably 
from Java, flashed out into a small figure with iridescent rings, and imme¬ 
diately retreated upon itself. A fourth, from the India Museum, of a light 
amber colour, required to be warmed. It formed a remarkable and beautiful 
figure, but the display of the usual phenomena was arrested by chilling, a 
dull frosty silvery appearance coming over the figure, which though very 
beautiful, prevented the film from telling its history. This oil set and became 
opaque a little below 50° F. A fifth specimen purchased by me seven or 
eight years ago in Prussia, gave a very good figure. 
Figs. 3 and 4 are portions of the figures of olive oil. Fig. 3 is from a 
specimen marked “ extra sublime,” Fig. 4 from a specimen marked “ Tuscany, 
fine.” The enormous demand for olive oil offers a great temptation to the 
use of cheaper oils. In this country the oil of sessame seed is used either in¬ 
stead of olive oil or for mixing with it, while in France poppy-seed oil is 
largely employed for the purpose. Figures of these are given, Fig. 5 being 
that of sessame, and Fig. 6 that of poppy.* These oils, together with lard 
oil, Fig. 7, are also used for mixing with some of the medicinal oils. 
A good deal of interest is just now felt respecting linseed oil. I have lately 
performed a number of experiments with it, an account of which I must re¬ 
serve until the Journal can better afford space for such minute details. 
I may, however, remark in conclusion that the greatest precaution must be 
taken in ensuring the purity of the glasses used in obtaining cohesion-figures. 
I have repeatedly found that after glasses have been used with fatty oils they 
produce nothing but failures, until they have been well washed with caustic 
potash or sulphuric acid. There may be cases where spirits of wine will be 
found more convenient than potash, especially in the case of some of the 
essential oils which do not readily saponify. 
P.S.—Since writing the above, I have made some inquiries respecting the 
commercial treatment of one or two of the oils operated on, and I have also 
visited the laboratory of a wholesale druggist, where castor oil, as imported, 
is purified by filtration through bags at a steam heat. 
* Tlie experiments which furnished these figures were performed in winter in a warm room 
and the oils had to be warmed before they could be used. 
