OF ORGANIC SUBSTANCES ON THE RAYS OF THE SPECTRUM. 269 
substance were a solid 0'2 gr. or 0 - 02 gr. in weight of the body were'dissolved in 
alcohol or water so as to form a total volume of 100 c.c., and when it was desirable to 
compare a liquid substance with a solid, both were weighed and dissolved in the same 
manner. In this way salicylate of methyl was compared with salicylic acid and 
salicine. 
Benzene (Diagram No. 6 ).—A very pure specimen, kindly lent us by Professor 
Guthrie. About ten ounces of the substance had been separated from more than a 
gallon and a-half of the commercial benzene, by successive crystallisations in a freezing 
mixture. The first feature noticeable here is the small alteration in the absorption of 
the rays caused by a dilution with 99 volumes of alcohol. It is impossible to describe 
the changes noticed on repeated dilutions without reference to the diagram, but 
it may be well to record the proportions of alcohol to benzene in the liquids photo¬ 
graphed. 
One part of benzene was successively diluted so as to measure 100 , 150, 190, 220 , 
235, 250, 375, 500, 750, 850, 1000, 1275, 1500, 2000, and 2500 times its original 
volume. With a dilution of 750, six absorption bands are seen. In other words, as 
the cell is § inch in thickness, a layer of benzene TFFofh °f an kicli in thickness would 
show the same spectrum. As the bands are perfectly well seen after a dilution of 
1500 times, it follows that a film of benzene fcmoth 0 f an inch in thickness would 
show them. 
Toluene. — Methylbenzene, BP. Ill 0 C.—The various solutions examined contained 
T(To, 500> Tooo» Folio) tstoo, and Food of their volume of the hydrocarbon. It is 
evident, from Diagram No. 7, that a similarity exists between this substance and 
benzene, though fewer rays are transmitted by toluene, which greatly modifies the 
appearance of the two diagrams. The two absorption bands between 17 Cd and 18 Cd 
are highly characteristic. 
Ethylbenzene, BP. 135°-6 (Diagram 8 ).—The solutions examined contained the fol¬ 
lowing volumes of the liquid, yyo, yoF Foo* TchTF 2000 > Audio FsTTF ToFF and Foote 
At 5770 a strong band of transmitted rays appears from about half way between 18 Cd 
and 23 Cd, and extends to 24 Cd; this widens out. until at xoVo if meets the narrow 
absorption band noticed in the previous spectrum as situated between 17 Cd and 18 Cd. 
Trimethylbenzene. — Mesitylene.— The methyl molecules occupy the position indicated 
by 1-3-5, BP. 163-4° C. (Diagram No. 9). Observations were made on solutions 
containing oxf 5 <3F TFdF Worn 3 F 0 F eooo and T0F00 of their volume of the liquid. 
A transmitted band occurs between 18 Cd and 23 Cd, commencing at - 50 F dilution. At 
277777 two narrow bands of transmitted rays occur between 17 Cd and 18 Cd. 
These hydrocarbons are the least opaque to the photographic rays of the many 
substances containing the benzene nucleus which we have examined, although compared 
with the substances previously treated of, namely, the alcohols, fatty acids, and ethereal 
salts, they are greatly wanting in transparency. 
We now pass to substances containing the hydroxyl group replacing hydrogen. 
