354 REPORT—1899. 
Parahydroxybenzoie Acid, C;H,(OH).COOH. 1: 4.. 
‘138 gram in 20 e.c. alcohol, 
With 5 mm. the spectrum extends to 1/\ 3359, and gradually extends 
to 1/X 3480 as the thickness of the layer of liquid is reduced to 1 mm. 
‘138 gram in 100 c.c. alcohol. 
With 5, 4, 3, and 2 mm. the spectrum extends to '/A 3480 (A 2875), 
With 1 mm. an absorption band appears from !/A 3525 to 4415. 
‘138 gram in 500 c.c. alcohol. 
With 5, 4, 3, 2, and 1 mm. an absorption band appears from 1/A 
3525 to 4415, which gradually gets narrower as the thickness of the 
layer of liquid is reduced. 
‘138 gram in 2,500 c.c. alcohol. 
With 5, 4, 3, and 2 mm. an absorption band appears from 1/A 3641 
to 4297, which gets narrower as the thickness of the layer of liquid is 
reduced. With 1 mm. the absorption band has disappeared, and the 
spectrum extends to!/A 4658. 
TAUTOMERISM. 
A Study of the Absorption Spectra of Isatin, Carbostyril, and their Alkyl 
Derivatives in relation to Tautomerism. (Hartiey and Dossis.)} 
The examination of absorption spectra has recently been successfully 
applied to the study of the relationship between compounds commonly 
described as tautomeric and desmotropic. In those cases, for example, in 
which a substance and two related isomeric alkyl compounds having 
respectively the lactam and the lactim constitution are known, it is un- 
certain whether the supposed parent substance has a constitution similar 
to that of either of the derivatives. Thus there are two methyl deriva- 
tives of isatin, the constitution of each of which has been satisfactorily 
determined from its chemical reactions, but there is no unquestionable 
evidence which proves that the constitution of isatin itself is similar to 
that of either of the derivatives. 
Tt is known that the substitution of a methyl or ethyl group for an 
atom of hydrogen, without other alteration in the structure of the sub- 
stance, merely increases the general absorption very slightly for each CH, 
added to the molecule,? that is, it slightly shortens the transmitted 
spectrum, but makes practically no difference in the character of the 
absorption ; for instance, it scarcely increases its intensity, nor does it 
convert a general absorption into one that is selective, or vice versd. 
The curves of molecular absorption of such substances afford the 
desired information concerning the relationship of their constitution to 
that of their respective derivatives. 
The spectra of carbostyril and methylpseudocarbostyril both show an 
absorption band in the same position, and the spectra of the two sub- 
stances are in other respects almost identical, the only difference being that 
the general absorption is slightly increased in the case of methyl- and 
ethylpseudocarbostyril, which is the effect usually produced when 
1 Trans. Chem. Soc.-1899, p. 640. 
2 Phil. Trans. vol. clxx, pt. 1, p. 267, 1879 
