OF ORGANIC SUBSTANCES ON THE RAYS OF THE SPECTRUM. 
2G3 
Ethylic Alcohol. Specimen No. 1.— This specimen was obtained from Mr. Kai-ilbaum, 
of Berlin. After rectification it boiled at 7'8°‘5. It exhibits slightly less transparency 
than methylic alcohol. 
Specimen No. 2.—A sample of ordinary commercial absolute alcohol obtained from 
Messrs. Burgoyne and Burbidges, BP. 79°. We tested two or three Winchester 
quarts of this liquid and made use of it for dissolving such substances as were insoluble 
in water. They yielded the same spectrum as Nos. 1 and 2. Several other samples 
we have examined are not of such great purity, although from the same firm. 
Propylic Alcohol. —This was carefully purified and redistilled, BP. 97°'5. It is a 
substance very difficult to dehydrate completely, but, as a trace of water does not affect 
its diactinic quality, this may be disregarded. It will be seen by a glance at the 
diagram that one cell-full of the liquid is less diactinic than ethylic alcohol, and that 
the absorption due to three times the thickness of one cell is not much greater than 
that caused by one cell only. As the specific volumes of the three alcohols are as the 
following numbers :— 
Methyl .40 - 8 
Ethyl ..62-8 
Propyl..8 4’8 
we may examine the liquids in what are nearly molecular proportions by taking layers 
of liquid differing in thickness in the proportions of 2, 3, and 4 according to the 
number of carbon atoms in the molecule. It will be seen that these three substances 
show a gradual increase in the absorption of the more refrangible rays corresponding 
to the size of their molecules, or, in other words, to the number of carbon atoms they 
contain. The increased absorption is perfectly evident whether we take equal volumes 
of the liquids or thicknesses proportional to their specific volumes, from which we may 
conclude that one cell-full of liquid exerts nearly the maximum amount of absorption 
of the substance. 
Normal Octylic Alcohol. —It has been shown that this substance is obtainable from 
the oil of Heracleum Spondylium. This specimen was prepared from heracleum oil 
by Mr. Kahlbaum. After purification it boiled at 192 0, 5 instead of at 198°, the 
correct boiling point. One cell-full of the liquid exerts a marked degree of absorption, 
though, judging from the alcohols previously examined, the spectrum is very much 
what one might expect from a substance containing as many as eight carbon atoms. 
It is worth remarking that the impure specimens of methylic and ethylic alcohols, 
when diluted with an equal or double volume of water, were perfectly diactinic. 
The Fatty Acicls. 
Formic Acid. Specimen No. 1 . —This acid was evidently very carefully prepared 
and of great purity ; it was said to be crystallisable at 48° F., though we did not succeed 
in obtaining it in the solid form. Obtained from Mr. Kahlbaum. 
