70 GIBBS. 
and in ‘snow and is the product of many oxidation and other chemical 
reactions which proceed with and without the influence of light. 
A. Richardson” has found traces of hydrogen peroxide in water exposed 
to sunlight and larger quantities in water acidified with sulphuric acid. 
Exposed to rays of low refrangibility, no hydrogen peroxide was formed. 
Water exposed to sunlight in presence of various substances such as ether, 
phenol, amyl alcohol, palmitic, stearic, and oxalic acids, some of the alka- 
loids and urine was found to contain hydrogen peroxide. In some cases 
the presence of water was found not to be necessary to the hydrogen 
peroxide formation. 
Dieudonné“ found that water exposed to light gave a weak reaction 
with Schénbein’s reagent and, if the ether used in the reagent was mixed 
with the water before the exposure, the test was more pronounced. 
C. T. R. Wilson*” has shown that sunlight has the power to produce 
showers or fogs when acting through a quartz window or even when a 
glass screen was interposed between the fog chamber and the sun. He 
has shown that Aitken’s failure to obtain this result was probably due 
to two causes; namely, insufficient expansion to produce condensation on 
the nuclei, and failure to test immediately, since such nuclei persist never 
longer than a few seconds. 
I will quote a few brief sentences from this highly interesting article. 
“It is plain, therefore, that sunlight, unlike the light from the other 
sources tried, contains nucleus-producing rays which can penetrate glass.” 
“The experiments described leave little room for doubt that pure oxygen 
and water vapour alone are sufficient to enable a cloud to be produced 
under the influence of ultra-violet light.” 
“In hydrogen, fogs could not be obtained under the influence of ultra- 
violet light without expansion.” 
“The view is here taken then, that under the action of the ultra-violet 
light small drops of water combine swith the oxygen in contact with 
them, and in consequence of the lowering of the equilibrium vapour pres- 
sure by the dissolved H:0. they are able to grow, when similar drops of 
pure water would evaporate.” 
“The absence of any effect of this kind in moist hydrogen is in agree- 
ment with the view that the growth of the drops in air or oxygen is due 
to the formation of hydrogen peroxide.” 
D’Arcy* has shown that hydrogen peroxide is decomposed by sunlight, 
and he obtained values which indicated that the days on which the radia- 
tion is most effective in decomposing hydrogen peroxide are also days 
on which the discharging of electrification is most pronounced. 
He states: 
“Tf the origin of the positive and negative ions in the air is due to the 
™ Chem. News (1889), 60, 255; Jowrn. Chem. Soc. London (1891), 59, 
51; (1898), 63, 1109; (1894), 65, 450; (1896), 69, 1349 and 1352. 
® Arb. a. d. kais. Gsndhtamte, A. 9, 537, through Chem. Centralbl. (1894), 
(2), 870. Also quoted by H. Thiele, Ztschr. f. ang. Chem. (1909), 22, 
2480, 
* Phil. Trans. Roy. Soc. London. (1899-1900), 192—A, 430. 
“ Phil. Mag. (1902), VI, 3, 42. 
