— 161 — 



gave for the acid the formula C 10 H 18 O 3 . It consisted of keto-men- 

 thylic acid, which had already been obtained by Arth as well as 

 by Beckmann and Mehrlander 1 ) by oxidation of menthol. In the 

 auto-oxidation of menthol, therefore, the ring opens, as shown in the 

 subjoined formulae: 



CO C H 2 COOH C H 2 



CH s\ / \ HO CH 3\ \ 



, )CH.CH CH.CH 3 + X= >CH.CO CH-CH, 



CH3/ \ / ° ch 8 / \ : / 



CH 2 CHj CH 2 CH 2 



Further additions to the knowledge of the chemical action of 

 light have been made by Ciamician and Silber 2 ) in the course of 

 investigations into the effect of light upon benzaldehyde. They dis- 

 covered that after exposing benzaldehyde to light from March 19 th 1905 

 to October 30 th 1907, there had formed in it a small quantity of white 

 crystals, insoluble in ether, which, when recrystallised from glacial acetic 

 acid melted at 245 to 2 4 6° and which, upon analysis, proved to be 

 identical with the trimeride of benzaldehyde (C 7 H 6 0) 3 , which had 

 already been described by Mascarelli 3 ). From the portion which was 

 soluble in ether there were isolated benzaldehyde, benzoic acid and 

 hydrobenzoin (m. p. 136 ) as well as a resin which, when purified by 

 dissolving it in ether, and precipitated with petroleum ether, appeared 

 in the form of a white powder, m. p. 160 to 170 . By determining 

 its molecular weight, in the supposition that it was a polymeric benzal- 

 dehyde, its formula (C 7 H 6 0) 4 was traced, and proved by the pre- 

 paration of the semicarbazone melting at 23 2°. This, upon analysis, 

 gave the figures foramono-semicarbazone of the tetrameric alde- 

 hyde. The authors surmise this tetrameride to be .a body constituted 



C 6 H 5 C 6 H 5 C 6 H 5 C 6 H 5 



I I I I 



CO C(OH) — C(OH) — CH-OH. 



Ciamician and Silber also report on the action of light upon safrol 

 and iso- safrol, as well as upon methyl- eugenol and methyl tso-eugenol 

 in the presence of iodine. 



Safrol and /^-safrol were exposed to light for a year, a trace of 

 iodine being added to them. At the end of that period the safrol 

 was found unchanged, while the w-safrol had been converted into a 

 brown mass of resin, interspersed with crystals of di-w-safrol (m. p. 145 

 to 146 , from alcohol). Methyl- eugenol and methyl zso-eugenol showed 

 similar differences in their behaviour, the former having undergone no 

 change in a year, while the latter had become converted into a mass 



x ) Liebig's Annalen 289 (1896), 369. 



2 ) Berl. Berichte 42 (1909), 1386. 



*) Gazz. chim. ital. 36, II. (1906), 670. 



11 



