OF THE VAPOURS OF BENZENE AND ITS HOMOLOGUES. 
523 
A narrow and feeble solution band was measured at A. 2330, which Friederichs 
considered as corresponding to a vapour band measured by him at \ 2305. It has a 
considerable intensity, inasmuch as it withstands dilution to a far greater extent than 
the band under discussion ; it is the eighth band. 
Furthermore, a ninth band has been photographed, which apparently corresponds 
to the ninth group of vapour bands measured by Friederichs (see p. 493). 
That six, and not seven, bands have generally been referred to as the characteristic 
feature of the benzene solution spectrum arises from the fact that six bands appeared 
to be similarly constituted, that is to say, each of them was sharpest and strongest at 
the more refrangible side, and became gradually weaker and less well defined on the 
side towards the red, but in the seventh feeble band this constitution was not evident. 
The greatest importance has always been attached to the four strongest bands, 
because, as already intimated, they are of similar intensity and constitution, and occur 
at approximately regular intervals. Moreover, there are similar groups of four bands 
in the spectra of naphthalene and anthracene (‘ Trans. Chem. Soc.,’ 1898, vol. 73, p. 695). 
The following tabulated statement of the numerical values in wave-lengths of the 
intervals (or transmitted rays) between each two successive absorption bands—that is 
to say, the space between the tail of the first and the head of the second band, and so 
on, with the differences between the more refrangible edges of successive bands—is of 
a particular interest in this connection :— 
Solution Bands of Benzene. 
(Hartley 
and 
Dobbie) 
Band. 
Intervals, or transmitted rays, separating successive bands 
o 
measured in Angstrom Units, with the 
wave-length measurements of the width of the bands. 
Differences in wave¬ 
lengths between 
the more refrangible 
edges of 
successive bands. 
I. 
2709 to 2681 
82 
Interval 63 
II. 
2618 to 2599 
58' 
45 
III. 
2554 to 2541 
56 
44 
f 
IV. 
2497 to 2485 
56 
!> * U 
V. 
2437 to 2429 
53 
„- 50 
VI. 
2379 to 2376 
46 
„ - 32 
VII. 
2344 to 2330 
The four principal solution bands are indicated by the bracket in the last column, 
° 
showing regular differences in wave-lengths varying between 58 and 53 Angstrom 
Units between the more refrangible edges of successive bands. 
