CHEMICAL ACTION OF ΤῊΒ SOLAR RADIATIONS. 155 
nature, organic or inorganic, is independent of the solar influences, although 
their scales of sensibility to them are widely different. 
There are a few remarkable chemical facts recorded, which prove yet further 
how very extensive is the operation of the actinic force, and point at the same 
time to a line of inquiry, which is only now beginning to engage attention. 
Dumas was the first to point out, that when crystallizable acetic acid 
C* Η Οὐ + HO is exposed to sunshine in an atmosphere of dry chlorine, it is 
gradually decomposed, and that an equal volume of chlorine completely takes 
the place of the hydrogen, a new acid composed of C4 C13 O3+4+HO 
(chloracetic acid) resulting*. 
Auguste Cahours has shown that some very striking effects are pro- 
duced by sunshine on the combination of chlorine and some ethers of the 
methylic series}. ‘‘ La préparation de l’oxalate et du formate de méthyléne 
perchlorés est des plus simples : il suffit, en effet, de placer ces produits bien 
purs et bien secs dans des flacons remplis de chlore desséché, puis d’exposer 
ces derniers ἃ la radiation solaire directe. Dans les premiers moments, l’at- 
taque est excessivement vive, mais elle se ralentit ἃ mesure que la chlorura- 
tion fait des progrés; on reconnait que l’opération est terminée, lorsque, aprés 
une exposition de plusieurs jours ἃ un soleil assez vif, la teinte de l’atmo- 
sphere du flagon ne s’affaiblit plus.” 
At the meeting of the British Association at Cork, Dr. Draper of New York 
communicated the very remarkable fact, that chlorine which has been exposed 
to daylight or sunshine possesses qualities which are not possessed by chlo- 
rine made and kept in the dark. It acquires from that exposure the property 
of speedily uniting with hydrogen, under circumstances in which the combi- 
nation with ordinary chlorine is effected with very great slowness. Dr. Draper 
found that if a flask of chlorine and hydrogen was placed in an atmosphere 
of chlorine, and then exposed to sunshine, no formation of hydrochloric 
acid took place. The agent producing the combination had been stopped by 
the yellow atmosphere of the chlorine surrounding the flash. It was now found 
that if this chlorine which had stopped the chemical agent, was itself mixed 
with hydrogen, it combined, under the influence of the weakest light, with an 
energy which unsolarized chlorine did not exhibit. Hence Dr. Draper inferred, 
«that those rays are absorbed by ponderable bodies, and that they become 
latent after the manner of heat {.” He also concludes, that the indigo rays are 
the mest active in effecting the formation of hydrochloric acid, and that the in- 
digo rays are absorbed by the solarized chlorine. That remarkable changes do 
take place under the influence of sunshine in elementary bodies is further shown 
by the experiments of Berzelius on phosphorus§. This chemist has proved 
that when phosphorus, dissolved in ether, oil, or hydrogen gas, is exposed to 
sunshine, it undergoes a peculiar modification, and separates under the form 
of red phosphorus; and that in the Torricellian vacuum it sublimes in red 
scales. 
I have also shown|| that a solution of protosulphate of iron in distilled 
water, (freed of, and carefully kept from the air,) exposed to sunshine, acquires 
a property of precipitating gold and silver from its solutions with much greater 
rapidity than a similar solution kept in the dark. In the same paper I have 
given some experiments, proving that with certain compounds precipitation 
* Sur les Types Chimiques, Ann. de Ch. et Ph. Ixxiii. 77. 
t Recherches relatives ἃ l’action finale du chlore sur quelques éthers composés de la série 
méthylique sous l’influence de la radiation solaire. _Comptes Rendus, xxiii, 1070. 
~ On Tithonized Chlorine. Philosophical Magazine, July 1844, 
ξ Traité, tom. i. 258. ἢ 
|| Contributions to Actino-Chemistry. Phil. Mag. 1845, 
