268 
MESSRS. W. 1ST. HARTLEY AND A. K. HLTNT1NGT0N ON THE ACTION 
(2.) The normal fatty acids exhibit a greater absorption of the more refrangible rays 
of the ultra-violet spectrum than the normal alcohols containing the same number of 
carbon atoms. 
(3.) There is an increased absorption of the more refrangible rays corresponding to 
each increment of CEL in the molecule of the alcohols and acids, 
(4.) Like the alcohols and acids the ethereal salts derived from them are highly 
transparent to the ultra-violet rays, and do not exhibit absorption bands. 
PART IT. 
Examination of Substances containing the Benzene Nucleus. 
In the examination of such substances as contain a closed chain of carbon atoms doubly 
linked together, one fact presented itself in a striking manner. All these bodies are 
strongly adiactinic, those which are the least so being the hydrocarbons ; Diagram No. 2, 
will at once make this apparent. Professor Stokes has pointed out that one of these 
substances, salicine, in an aqueous solution, the strength of which is not stated, shows 
a characteristic absorption band. Now salicine is a substance the constitution of which 
is perfectly well known : it is a glucoside of saligenin, 
C fl H u 0 5 
C 6 H 4 (OH)CH 3 
and consequently the absorption band may be due to the saligenin. At any rate it 
seemed worth while to dilute solutions of known strength, containing such allied 
substances as phenol, salicylic acid and salicylate of methyl, and ascertain whether any 
absorption bands are thus made visible. The result has disclosed the fact that almost 
if not entirely all benzene derivatives, including the hydrocarbon itself, are characterised 
by one or more absorption bands, which resist modification or extinction by dilution to 
an enormous extent. 
For this part of the research it has been necessary to make solutions of known 
strength, to dilute them with definite quantities of water, and photograph the various 
liquids thus obtained. These photographs have been placed upon sectional paper, 
upon which the lines of cadmium as seen in a photograph of the metallic spectrum 
have been drawn, and the proportions of substance in solution have been co-ordinated 
with the position of the absorption bands relative to the cadmium lines. A series of 
curves has thus been obtained, and each of these proves to be a highly characteristic 
feature of the substance observed. The number of photographs necessary for com¬ 
pleting the curves has varied very much with different substances, sometimes four or 
five, and occasionally eighteen or twenty have been taken. 
When the substance to be examined was a liquid, two cubic centimetres were 
measured and diluted with alcohol if necessary, or water if possible, so as to form a 
total volume of 100 c.c. From this solution others more dilute w r ere obtained, If the 
