NEW CHEMICAL REACTIONS. 79 
vapor of the nitrite was derived from a portion of its liquid 
which had been accidentally introduced into the passage 
through which the dry air flowed into the experimental tube. 
In this case, the electric beam traversed the tube for 
several seconds before any action was visible. Decomposi- 
tion then visibly commenced, and advanced slowly. When 
the light was very strong, the cloud appeared of a milky 
blue. When, on the contrary, the intensity was moderate, 
the blue was pure and deep. In Briicke's important ex- 
periments on the blue of the sky and the morning and 
evening red, pure mastic is dissolved in alcohol, and then 
dropped into water well stirred. When the proportion of 
mastic to alcohol is correct, the resin is precipitated so 
finely as to elude the highest microscopic power. By re- 
flected light, such a medium appears bluish, by transmitted 
light yellowish, which latter color, by augmenting the 
quantity of the precipitate, can be caused to pass into 
orange or red. 
But the development of color in the attenuated nitrite- 
of-amyl vapor is doubtless more similar to what takes place 
in our atmosphere. The blue, moreover, is far purer and 
more sky-like than that obtained from Briicke's turbid 
medium. Never, even in the skies of the Alps, have I 
seen a richer or a purer blue than that attainable by a suit- 
able disposition of the light falling upon the precipitated 
vapor. 
Iodide of Allyl. Among the liquids hitherto subjected 
to the concentrated electric light, iodide of allyl, in point 
of rapidity and intensity of action, comes next to the 
nitrite of arnyl. With the iodide I have employed both 
oxygen and hydrogen, as well as air, as a vehicle, and found 
the effect in all cases substantially the same. The cloud- 
column here was exquisitely beautiful. It revolved round 
the axis of the decomposing beam; it was nipped at certain 
places like an hour-glass, and round the two bells of the 
glass delicate cloud-filaments twisted themselves in spirals. 
It also folded itself into convolutions resembling those of 
shells. In certain conditions of the atmosphere in the Alps 
I have often observed clouds of a special pearly luster, 
when hydrogen was made the vehicle of the iodide-of-allyl 
vapor a similar luster was most exquisitely shown. With 
a suitable disposition of the light, the purple hue of iodine- 
vapor came out very strongly in the tube, 
