264 SCIENCE PROGRESS 



carbons as toluene, the xylenes and />-cymene by oxygen and 

 water under the influence of sunlight. Toluene is converted 

 into benzoic acid (small quantities of benzaldehyde being also 

 formed) ; the xylenes give the corresponding toluic acids (with 

 traces of the corresponding phthalic acids), whilst />-cymene 

 gives /-cuminic acid, C 3 rV . C 6 H 4 . COOH, together with 

 />-hydroxyisopropylbenzoic acid, OH . CMe 2 . C 6 H 4 . C0 2 H and 

 /-propenylbenzoic acid, CH 2 : CMe . C 6 H 4 . C0 2 H. 



Formic acid is formed as well in all cases. Oxidation does not 

 take place in darkness. It is interesting that the nitrotoluenes 

 do not undergo oxidation under the same conditions. 



Neuberg ! has recently shown that uranyl salts act catalyti- 

 cally in accelerating the oxidation by air of numerous organic 

 compounds exposed to sunlight ; iron salts act similarly. 2 An 

 especially interesting case of oxidation brought about in this 

 way is that of benzoic acid to salicylic acid : 



C 6 H 5 C0 2 H -> OH . CH, . C0 2 H 



The autoxidation of menthone is dealt with in Section VI. 



III. Polymerisation 



Among the earliest cases of photochemical action studied 

 were those which involve the polymerisation of unsaturated 

 compounds : thus acetylene is transformed into benzene, brom- 

 acetylene, CH • CBr, into syw.-tribromobenzene, propiolic acid, 

 CH • C. C0 2 H, into trimesic acid (syw.-benzenetricarboxylic acid), 

 anthracene into dianthracene (Fritzche, 1866), whilst acridine, 

 anthranol and methylanthracene also give rise to polymeric 

 forms. In the case of anthracene, the action is reversible and 

 has been studied by Luther and Weigert 3 from the physical 

 standpoint in considerable detail. 



Thymoquinone was shown by Liebermann and Ilinski 4 to 

 polymerise rapidly to dithymoquinone and this change was 

 further studied by Ciamician and Silberin 1886 5 ; the conversion 



1 Biochem. Zeitschr. 1908, 13, 305. ■ Ibid. 1910, 29, 279. 



3 Luther and Weigert, Zeii. physikal. Chetn. 1905, 53, 416 ; Weigert, ibid. 1908, 

 63, 458. 



« Ber. 1877, 10, 2177 ; 1885, 18, 3193. 

 5 Gazzetta, 1886, 16, III. 



