644 
MESSRS. T. E. THORPE AHD J. W, RODOEP OH THE RELATIOHS 
Sulphide. 
“ Rest ” 
\ / 
(calculated). 
S. 
//d- (observed). 
Methyl. 
578 
329 
249 
Ethyl. 
812 
569 
243 
]\Ieaii value of S = 246. 
Influence of Ring-grouping. 
Horstmann’s discussion of the specific molecular volumes of liquids seems to show 
that in aromatic compounds the ring-grouping of atoms exerts a marked influence, 
On the other hand, Bbuhl concludes that, so far as refraction and dispersion con¬ 
stants go, there is no indication of this effect. Bruhl assumes, however, that three 
double linkages occur in the benzene nucleus. 
The data to test this point in connection with the viscosity constants are but 
scanty, and, farther, four of the aromatic compounds—the methyl toluenes—are 
isomers, each having a different viscosity magnitude. 
Since the value of CHg deduced from homologous aromatic hydrocarbons agrees 
with the values given by other homologous series, in the present state of the question 
it may be assumed that carbon and hydrogen have the same values in these com¬ 
pounds as they have in the others. In the following table the “rests” are calculated 
from the previously found values for carbon and hydrogen on the assumption that 
the constitution is the same as in an open straight chain compound. The differences 
in the last column represent the excess of the observed molecular viscosities over the 
values thus calculated, and may be taken as measures of the effect of the ring¬ 
grouping of atoms. 
rjd? (observed) 
“ Rest ” 
(calculated). 
Ring-grouping. 
Benzene. 
688 
453 
235 
Toluene . 
821 
573 
248 
Ethyl benzene. 
939 
693 
246 
Ortho-xylene. 
954 
693 
261 
Meta-xylene. 
939 
693 
246 
Para-xylene. 
923 
693 
230 
Mean value for ring-grouping = 244. 
