CHAPTER VI 



THE ACTION OF LIGHT RAYS ON ORGANIC COMPOUNDS, AND 

 THE PHOTO -SYNTHESIS OF ORGANIC FROM INORGANIC 

 COMPOUNDS 



IN this chapter it will be shown that, in addition to salts of iron, 

 a considerable number of other inorganic salts in dilute solution in 

 water, and in either crystalloidal or colloidal solution, possess 

 activity as transformers in the action of light on water and carbonic 

 acid ; next, the action of light upon formaldehyde at higher concen- 

 tration will be considered to show how more complete organic com- 

 pounds arise; and, finally, the action of light upon organic bodies 

 of more complex nature still, such as carbohydrates, proteins, 

 vegetable and animal juices and extracts, and other substances of 

 biochemical interest will be described. 



Photo- Synthesis by Inorganic Transformers. In a previous 

 chapter it has been mentioned that oxide of uranium in the colloidal 

 state gives a far greater photo-synthetic effect than the crystalloidal 

 salts, and the inference was drawn that the state of aggregation of 

 the colloid was favourable to the reaction. Accordingly in the 

 earlier experiments with iron compounds, colloidal ferric oxide was 

 employed. Continued investigation of the iron compounds has, 

 however, shown that the size of the solution aggregate may easily 

 become too great, and that there is a certain degree of aggregation 

 at which the catalytic action has an optimum value. 



Thus, while dialysis of uranium oxide gives a condition in which 

 the photo-synthetic effect is much greater than that obtained with 

 an equal concentration of uranium nitrate in crystalloidal condition, 

 dialysis of iron compounds, on the other hand, gives a condition in 

 which less effect is obtained than with an equal concentration of 

 ordinary ferric chloride. 



It is to be remembered, however, that there is often in the case 

 of ordinary solutions of salts of heavy metals a good deal of complex 

 formation approaching a colloidal condition. This is shown, for 

 example, in the case of solutions of cupric salts by the apparent lack 

 of agreement between the molecular weights as deduced by the 



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