OF THE VAPOURS OF BENZENE AND ITS HOMOLOGUES. 
477 
1 litre ot water. The volume of air aspirated through the benzene in each experiment 
could be exactly measured; it served to vaporise the liquid and charge the tube 
with vapour. After using the aspirator for a few minutes the taps were closed 
and the temperature taken by a thermometer kept in the bath, the liquid in 
which was constantly stirred. In front of the end of the tube is a quartz lens, and 
behind the lens the electrodes which give the emission spectrum, the rays being 
focussed upon the slit of a quartz spectrograph. 
The plates were exposed from two to five minutes, but as a rule the exposure was 
not more than two minutes. After one exposure the temperature of the bath was 
raised and another exposure made immediately below the first, and so on, going 
through the same manipulations as for the previous exposure. From the vapour- 
pressure curve and the ascertained temperatures in the bath the quantity of benzene 
presumably in the tube at each exposure was calculated. 
The actual quantity of the hydrocarbon present in the tube was afterwards 
determined by the gas analysis of its contents at the different temperatures. 
The capacity of the tube was 79 c.c. and its length 150 mm. It will be seen 
that, as the calculated and found quantities at 12°‘7 C. are very nearly the same, 
the molecule of benzene in a state of vapour is the same at temperatures below 
its boiling-point as at 20° C. above it. At higher temperatures the analytical data 
show that the air was far from saturated with the vapour, inasmuch as at 53° C. 
there were only 6 mgrm. more of benzene in 79 c.c. than at 12°*7 C., whereas the 
calculated quantity is 72 mgrm. more. 
The Contents of the Tube. 
Temperatures. 
Vapour pressures of 
benzene. 
°C. 
mm. 
12-7 
53 
25-7 
95 
43 
205 
53 
297 
Weight of benzene. 
Calculated. 
Found. 
grm. 
grm. 
0-0184 
0‘0179 
0-0316 
0-0203 
0-0643 
0-0211 
0-0904 
0-0239 
As the results of the gas analyses were not altogether of a character to be relied upon, 
another series of determinations was made by burning the vapour in a combustion 
tube with cupric oxide and weighing the products of combustion. In this way also 
it was found that the results obtained were very irregular, and after many combustions 
had been repeated, which yielded figures varying in an unaccountable manner, it was 
concluded that to ensure a determination of the amount of benzene under examination 
in each case a very complicated apparatus would have to be constructed, all the tube 
