362 
PROFESSOR TYNDALL ON THE ACTION OF RAYS 
cloud particles formed being very coarse. In four minutes the anterior two-thirds of the 
tube were filled with a very coarse cloud, the remaining third with a finer one. The 
whole rotated round a longitudinal axis, and the finer portion was rolled into a curious 
spiral form, and was tinged throughout with iridescent colours. The normal polar- 
ization was almost nil , except in the finer part of the cloud, which was slightly blue. 
II. Air and nitrite-of-amyl vapour .... 8 inches ; then 
Air and nitric acid 8 inches. 
The tube was optically empty for an instant only, a dense precipitation occurring im- 
mediately upon the concentrated beam. The distant part of the tube, however, was but 
scantily filled, showing the sifting action of the nitrite vapour. On reversing the tube 
copious precipitation occurred. After ten minutes’, exposure the particles tended to 
settle at the bottom of the tube. 
III. Air and nitric acid ........ 1 inch ; then 
Air and nitrite-of-amyl vapour . . . . 15 inches. 
The tube was optically empty only for an instant ; as in the last experiment, a dense 
cloud was immediately precipitated on the cone of rays. Here also the distant end of 
the tube was protected by the vapour in front. 
In all these cases the action was distinctly less energetic than when the nitrite vapour 
mixed with air alone was exposed to the light ; and very much less energetic than when 
hydrochloric acid was mixed with the vapour. 
Nitrite op Butyl (C 4 H 9 ONO):— A transparent yellowish liquid. 
This substance gives no sensible action with nitric acid ; but with hydrochloric, as 
already mentioned, the action is vigorous and brilliant. Here are a few of the results. 
Contents of experimental tube. 
I. Air and nitrite-of-butyl vapour 1 inch ; then 
Air and hydrochloric acid 15 inches. 
The action began a quarter of a minute after starting, a very white and brilliant cloud 
forming upon the concentrated beam and quickly spreading throughout the tube. 
II. Air and nitrite-of-butyl vapour .... 8 inches ; then 
Air and hydrochloric acid .8 inches. 
The action began about half a minute after starting, a cloud of comparatively fine 
particles being precipitated in the cone of rays, while the distant part of the tube was 
filled with coarse particles. The cloud was coarser, and the action less energetic than 
in the last experiment. 
III. Air and hydrochloric acid 1 inch; then 
Air and nitrite-of-butyl vapour . . . „ 15 inches. 
