162 LIGHT AND PROTOPLASM [Cn. VII 



not the results of the heat of sunlight. Most of these chemi- 

 cal effects may be grouped under four heads. 1. Synthetic ; 

 2. Analytic ; 3. Substitutional ; and 4. Isomerismic and Poly- 

 mer ismic. A few others may be classed (5) as fermentative. 

 Let us now consider each of these five classes.* 



1. The Synthetic Effects of Light will be considered chiefly 

 with reference to organic compounds. All the cases I have 

 gathered fall into three groups : addition to the organic com- 

 pound either (a) of oxygen, (/3) of chlorine or bromine, or 

 (7) of another organic compound. 



Among the compounds which take up oxygen is bilirubin, 

 C 32 H 36 N 4 O 6 , a solution of which, in sunlight, even when air is 

 excluded, oxidizes to biliverdin, C 32 H 36 N 4 O 8 . In the absence 

 of sunlight this change requires air (B. Ill, 418). DUCLAUX 

 ('87, p. 353) finds that vegetable oils, such as olive or palm 

 oils, are rapidly oxidized if exposed to light. CHASTAIGN ('77, 

 p. 198) believes this oxidizing action of light upon organic com- 

 pounds to be of very wide-spread occurrence ; the blue-violet 

 part of the spectrum being, in this respect, the most active. 



The direct combination by means of light of a halogen and 

 another substance is also not rare. Thus, in daylight, hydro- 

 gen unites with chlorine explosively. It unites with bromine 

 also, although with difficulty. Similarly, equal volumes of 

 chlorine and carbon monoxide unite quickly in the sunlight or 

 magnesium light to form carbon monoxid chloride, COC1 2 

 (B. I, 546). Again, when chlorine is passed through alcohol 

 under the influence of strong sunlight or magnesium light the 

 two substances unite and produce chloral hydrate (STREET and 

 FRANZ, '70). Likewise, when chlorine is passed, in sunlight, 

 through a solution of C 3 H 2 C1 2 O 2 in CS 2 , there is formed 

 C 3 H 2 C1 4 O 2 , two atoms of Cl having been added. Finally, 

 C 2 C1 6 may be made by uniting C 2 C1 4 and C1 2 in sunlight (B. I, 

 158) ; and the compound C 2 H 4 FeBr 2 2H 2 O may be made by 

 passing, in sunlight, C 2 H 4 through a concentrated aqueous 

 solution of FeBr 2 (B. I, 113). 



* Most of these cases were obtained by searching through BEILSTEIX ('86-'93). 

 References to this book will be made throughout this section by the letter B, 

 followed by the number of the volume and page upon which the statement may 

 be found. 



