SCIENTIFIC NOTES. 141 
most essential oils possess of rotating the plane of a polarised ray of light, 
Mr. Evans had arranged a polariscope, by means of which the exact 
amount of this rotatory power could be measured. The application of 
this test was simple, and the apparatus easily and inexpensively con- 
structed by anyone possessing a microscope provided with polarising 
prisms. Having determined the amount of rotation in degrees possessed 
by well-accredited samples of pure oil, and also of the supposed or 
possible adulterants, it becomes a simple matter of calculation to deter- 
mine the amount of adulteration ; for it is proved by experiment that 
the degree of rotation recorded is the mean of the combined rotating 
force of each of the components. The subject was illustrated by tables 
of values of pure and adulterated samples of various essential oils. 
On Cotton-seed Oil, and its Detection when Mixed with 
Other Oils. By R. Reynolds.— The author stated that large quantities 
of cotton seed were now being pressed for oil, the whole of this seed having, 
until the last few years, been thrown away or returned to the soil as a 
fertiliser. The weight of seed produced by each plant was three times 
as great ae that of the cotton which it yielded. Hence large quantities 
might always be relied on, and the cheap price of the oil might be 
expected to continue. The refining of the oil by an alkaline solution 
presented some singular features, and hopes had been entertained of 
producing available dyes, but hitherto these had been disappointed. 
Mr. Reynolds reported his experiments on the detection of this oil when 
mixed with olive oil, and considered that a solution of nitrate of mer- 
cury, known as Poutet's test, was sufficient for this purpose, if certain 
precautions were taken. With olive oil the test produced a hard friable 
mass : with olive oil adulterated with the cotton-seed oil it produced a 
more or less pasty substance. 
On the Amount of Tannin in British Galls at Various 
Periods of their Growth. By W. Judd. — Old galls which had remained 
on the oaks till after Christmas, and had, of course, been perforated by 
the fly, were found to contain 16 per cent, of tannin. Mature galls, but 
from which the fly had not escaped, yielded between 17 and 18 per 
cent., while half- developed galls afforded only 13 to 14 per cent. 
Though Aleppo galls contain two or three times this amount of tannin, 
still English galls, the author thought, could be economically used in 
dyeing, ink-making, tanning, &c, if collected at the proper period of the 
year. 
Note on Italian Castor Oil. By J. Phillips. —-This colourless, 
inodorous, and almost tasteless variety of castor oil was prepared, the 
author said, in the summer time from, seeds collected the previous autumn. 
The outer skin of the seed was removed by slight blows of a hammer, the 
seed being placed on a marble slab ; the decorticated portions were then 
submitted to gentle and continuous pressure, and the exuding oil filtered 
with as little exposure to air and light as possible. This oil was expensive, 
and, therefore, seldom exported. A much cheaper variety, made with far 
