274 ACTION OF ORGANIC SUBSTANCES ON THE RATS OF THE SPECTRUM. 
The solutions of tyrosine examined contained -g-jSpj, tckTo? TWo~o> anc ^ Wooo °f their 
weight of the substance. 
Phlorizine (Diagram No. 27).—It was considered of interest to examine this 
substance, since it is a glucoside containing the residue of phloroglucin, a body 
isomeric with pyrogallol, and phloretic acid an oxyphenyl-propionic acid. Solutions 
containing the following proportions of the substance were taken : -^g-, 57 , 0 , - 5 ggg -, twoo? 
T soo 0 ) 3 oooo ? and 50 q 00 . The absorption band is well defined and of great intensity; 
the second band of transmitted rays appearing at -5 o' occupies the same position 
as that seen in tyrosine, though there is not much resemblance between the curves 
of these two bodies. 
It is evident that most interesting results may be anticipated from a continuation 
of this research, and this contribution must be accepted as rather the bare commence¬ 
ment of the subject than its conclusion. 
The following is a summary of the chief points of interest appertaining to benzene 
and its derivatives : — 
( 1 .) Benzene and the hydrocarbons, alcohols, acids, and amines derived therefrom 
are remarkable—first, for their powerful absorption of the more refrangible 
rays; secondly, for the absorption bands made visible by dissolving them 
in water or alcohol; and thirdly, for the extraordinary intensity of these 
absorption bands : that is to say, their power of resisting dilution. 
( 2 .) Isomeric bodies containing the benzene nucleus exhibit widely different spectra, 
inasmuch as their absorption bands vary in position and in intensity. 
( 3 .) The photographic absorption spectra can be employed as a means of identifying 
organic substances and as a most delicate test of their purity. The curves 
obtained by co-ordinating the - extent of dilution, or in other words the 
quantity of substance, with the position of the rays of the spectrum trans¬ 
mitted by the solution, form a strongly marked and highly characteristic 
feature of very many substances. 
