1912-13.] The Absorption of Light by Inorganic Salts, No. XI. 165 
benzene in ethyl alcohol in the ultra-violet, and have examined the various 
views, but am afraid that none can be regarded as satisfactory. 
In connection with the critical attitude of this paper it should be 
remembered that the difficulty in establishing laws for the behaviour of 
absorption spectra is due to their being so extraordinarily characteristic. 
In this series of papers we have obtained values of A, the molecular 
extinction coefficient, ranging all the way from 27,000 to 001, and A can 
be measured for an aqueous solution for all wave-lengths between *23 fi 
in the ultra-violet and 13 /a in the infra-red. Molecular refraction 
and the other additive properties of physical chemistry are not very 
characteristic. 
(. Issued separately April 22, 1913.) 
