OF ORGANIC SUBSTANCES ON THE RAYS OF THE SPECTRUM. 
273 
yellow, and more than 16,000 parts of water do not yield a solution which is colourless 
when an inch of liquid is examined. 
Solutions were made containing the following proportions of the salt by weight:— 
i _ _i_ i i i_ i i i_ nnf i _i_ 
6000) 8000) 16000) 20000) 32000’ 40000) 50000) 55000) cUiLl 60000- 
The curve representative of this substance is very remarkable. The chief features 
are a narrow band of transmitted rays which must be almost contained within the 
visible spectrum, which scarcely increases in width even in presence of 16,000 parts 
of water, together with a second more refrangible group of rays between 17 Cd and 
23 Cd, which widens out very considerably. 
Meta-nitraniline, C G H 4 .NQ 2 .NEL, 1 ‘3 (Diagram No. 24).—This body was observed 
in aqueous solution, containing the following proportions of substance: yygy, FoVo) 
_1__1_ _i__ 1_ 1_ 1_ 1_ aiir i _1_ 
6000) 7000’ 8000) 20000) 28000) 40000) 60000> dau 100000- 
The chief feature in the curve derived from the spectra of this subtance is the long, 
straight, almost unaltered absorption band at about 9 Cd, which stretches from 8000 
to 40,000. 
There is still absorption near 23, 24, 25, and 26 Cd, in presence of 120,000 parts of 
water. 
Para-nitraniline, 1 '4 (Diagram No. 25).—Solutions containing j - 0 J q- 0 -, - %q 0 q , yp u, 7 o) 
20000 , 40 ooo ) ooooo -) anc I T o F o o o parts by weight of the substance were examined. 
The general appearance of the curve representing this body resembles in a striking 
degree that belonging to the corresponding nitrophenol. The absorption band which 
in presence of 50,000 parts of water lies between the air-line and 10, Cd continues, 
though narrowed and much enfeebled, until double this dilution has been effected. 
Throughout the various dilutions the blue and violet rays were absorbed, although 
more refrangible rays were transmitted. 
The following examples afford an instance of one of the applications of this kind of 
work to the purposes of research. 
Tyrosine was for some time considered by Barth and other chemists to be a deri¬ 
vative of paroxy-benzoic acid, but more recently it has been regarded as an oxyphenyl- 
amido-propionic acid, 
c 6 h 4 ( oh 
L GjH^NH^COOH. 
But these views have not been confirmed by the synthesis of the substance. 
If it be a derivative of paroxy-benzoic acid it may be expected to partake of the 
peculiarities of this substance in its action on the ultra-violet rays of the spectrum. 
We have accordingly examined solutions of tyrosine (see Diagram No. 26), and find 
that it more nearly resembles a phenol in actinic quality than an acid in which the 
carboxyl group replaces hydrogen in the benzene nucleus. Hence the latter view of 
its constitution, which represents the group oxyphenyl as substituting hydrogen in 
amido-propionic acid, is more correct than the former, since it is in accordance with 
its optical character. 
MDCCCLXX1X. 2 N 
