OF HIGH EEFEAN GIBILITY UPON GASEOUS MATTEE. 
359 
quantities were 6 inches to 6, 10 inches to 10, or 15 inches to 15, there were invariably 
particles. In some of the experiments it seemed as if the chemical attractions were 
satisfied before the light started, the subsequent action being very feeble. In other 
instances this did not seem to be the case ; for though the particles existed, the spaces 
between them became immediately filled by a fine dense cloud when the beam passed 
among them. In some instances the precipitation was exceedingly sudden and copious. 
Mr. Cotteell, who has assisted me with zealous intelligence in these experiments, thus 
describes one result. “ Some coarse particles were in the tube on commencing, and 
these, when the light was started, remained perfectly tranquil for a moment ; but after 
an instant’s pause the beam appeared to pierce like a ploughshare the cloud it had 
formed, throwing right and left of it heaps of precipitated particles. This cloud filled 
the tube almost instantaneously.” 
To give the benzol and nitric acid more time to act upon each other, on Tuesday 
evening, the 16th of February, 2 inches of each were admitted into the experimental 
tube, and allowed to remain there through the night. Sixteen hours subsequently the 
beam was permitted to act upon the mixture. The tube which contained it was to all 
appearance absolutely empty ; no particles whatever had formed during the night. In a 
quarter of a minute after starting the lamp chemical action began, and in five minutes 
the beam had filled the tube with a dense cloud. 
The deportment of benzol may be thus summed up : — 
Benzol. Nitric acid. 
2 inches. 2 inches. 
No particles; strong actinic action. 
4 
4 
5 5 ^ 55 
No particles; very strong actinic action. 
5 
„ 5 „ 
Particles; dense actinic cloud precipitated among them. 
6 
» -6 „ 
* • „ sometimes „ „ 
10 
„ io „ 
,, sometimes ,, „ 
15 
„ 15 „ 
„ sometimes ,. „ 
1 
„ 15 „ 
No particles; strong actinic action. 
15 
?? 1 ;; 
Particles. 
Iodide of Allyl (C 3 H 5 1) : — A transparent yellowish liquid. 
Contents of experimental tube. 
I. Air and iodide-of-allyl vapour ... 1 inch ; then 
Air and nitric acid 15 inches. 
The beam traversed the tube for an instant as if the space within it were a vacuum, 
but in the fraction of a second a brilliant shower of particles fell upon the beam. The 
cloud became coarse immediately. The action occurred in the anterior part of the 
tube, the most distant part being apparently , free from action. This is quite different 
from the deportment of iodide of allyl and hydrochloric acid. On reversing the tube 
another cloud, of finer texture than the first, was precipitated. The cloud assumed, 
3 b 2 
