§2] CHEMICAL ACTION OP LIGHT 163 



Important cases of the direct synthesis of organic compounds 

 are given by Klinger and Standke ('91). These authors 

 have shown that in sunlight (and not in the dark) phenanthren- 

 chinon unites directly -with benzaldehyd to form a third com- 

 pound phenanthrenhydrochinonmonobenzoat, in accordance 

 with the formula : Cj^HgO^ + C5H5CHO = Cj^Hg (OH) 

 (O ■ CO CgHg). Again, chinon (benzochinon) and benzaldehyd 

 may unite in the sunlight to form benzohydrochinon, according 

 to the formula : CgH^O^ + CgHgCHO = CgHgCO C6H3(OH)2. 

 Finally, benzochinon and isovaleraldehyd may similarly unite 

 to form isovalerochinhydron, thus : CgH402 + C^HgCHO = 

 C^HgCO CgH3(HO)2. These cases, then, are examples of 

 organic compounds which are wholly indifferent in the dark, 

 but which, subjected to strong sunlight, lose their identity by 

 uniting directly; they may sufiS.ce to illustrate the important 

 synthetic effect of sunlight on non-living, organic compounds. 



2. Analytic Effect of Light. — Cases of this effect are nu- 

 merous, varied, and striking. I will cite a few. The organic 

 dibasic acids C„H2„^04 break up in the sunlight and in the 

 presence of a small quantity of uranium oxide, into COg and 

 an acid C^Hg^Og (B. I, 63). For example, oxalic acid, CjHgO^, 

 breaks up thus into formic acid, CH^Oj and COg. Also an 

 aqueous solution of butyric acid, C^HgOj, in the presence of 

 uranyl nitrate, breaks up, in the sunlight, into COj and 

 CgHg (B. I, 422). We have seen that chlorine will unite 

 directly with organic compounds under the influence of light ; 

 on the other hand, compounds containing chlorine may lose it 

 in the sunlight. Thus under these conditions the ketone 

 (CgHj^NO • HCl)2PtCl4, an ammoniacal derivative of acetone, 

 becomes (CgHi^NO • HCl)2PtCl2; and (CgHj^NO ■ HCl)2PtCl4 

 becomes (CgHi^NO • HCl)2PtCl2^(B. I, 982, 983). Again'^ chlo- 

 rine acetate, CI • O • CjHgO, undergoes slow decomposition in 

 the light (B. I, 462) ; C5HgCl2, a derivative of pentine, CgHg, 

 does the same ; and ethylester, CIO • CgHg, explodes in sunlight. 

 Similarly explosive in sunlight is the greenish oil distilled when 

 absolute alcohol is poured over dry calcium chloride (B. I, 223). 

 Finally, sugar (Duclaux, '86, p. 881) and oxalic acid (Downes 

 and Bltjnt, '79, p. 209) are oxidized and break up into water, 

 carbon dioxide, and other compounds. These cases may serve 



