OF THE VAPOURS OF BENZENE AND ITS HOMOLOGUES. 
489 
Photographic 
plate II., 
No. 14. 
(Fig. 3.) 
mm. 
Bands. 
'At 
767 
5 
55 
591 
9 
55 
484 
9 
A great general 
absorption extinguishes 
nearly all the bands, then 
1 
J ” 
333 
12 
a gradual increase in their number 
follows on reduction of 
55 
206 
13 
pressure, the 
increase being at the less refrangible end of the 
55 
142 
11 
spectrum. 
55 
99 
14 
- 55 
88 
15 
At 100° C. and different pressures :— 
mm. 
Bands. 
Photographic 
rAt 92 
25 
plate IIP, < 
„ 69 
36 
No. 15. 
h „ 43 
50 
(Not reproduced.) 
At these reduced pressures there is a large increase in the number 
of bands; the principal groups of hands are all visible. 
(Fig. 4.) 
mm. 
Bands. 
r At 
67 
5 
31 
55 
52 
5 
54 
55 
37 
5 
60 
Photographic 
5 5 
28 
5 
72 
plate IV., 
55 
22 
5 
75 
No. 16. 
55 
15 
5 
88 
55 
9 
0 
52 1 
55 
5 
0 
38 
- ” 
4 
0 
30 J 
The barometer stood at 757 mm. There is a large and regular 
increase in the number of the bands on reduction of pressure as 
far as 15 • 5 mm. The effect of the general absorption and of the 
selective absorption is well seen. There is at pressures varying 
from 9 mm. to 4 mm. a gradual decrease in the number of bands 
on reduction of pressure, because, although the bands in the 
centre of the spectrum are visible, those at the less refrangible 
end, which at 767 mm. pressure are well seen, do not now appear, 
the quantity of substance being insufficient. In fact, there is at 
first a shifting of the general absorption towards the less refran¬ 
gible rays, and subsequently the bands seen at this end are 
extinguished. The regularity in the variation of the spectra is 
obvious on photographic plates II. and IV. (Nos. 14 and 16). 
In conclusion I have much pleasure in acknowledging the great care with which 
my assistant, Mr. A. G. G. Leonard, A.Pt.C.Sc.I., has photographed and accurately 
measured all of the vapour spectra of benzene and its homologues under different 
conditions, and the precise account he has rendered of the numerous analyses of the 
vapours, which were performed in different ways. 
3 R 
VOL. CCVIII.—A. 
