Action of Light Rays on Organic Compounds. 169 



made in certain of our experiments to obtain roughly quantitative results by 

 colorimetric comparison with diluted solutions of formaldehyde used as 

 controls. 



Three types of experiment have been carried out, viz. : (A) a considerable 

 number of inorganic salts in dilute solution in water, and in either crystalloidal 

 or colloidal solution, have been tested as to their activity as transformers in 

 the action of light on water and carbonic acid ; (B) the action of light upon 

 formaldehyde at higher concentration has been investigated; and (C) the 

 action of light upon organic bodies of more complex nature, such as carbo- 

 hydrates, proteins, vegetable and animal juices and extracts, and other 

 substances of bio-chemical interest has been studied. The results will be 

 described in corresponding sections of this paper. 



A. Photo-synthesis hy Inorganic Transformers. 



In the previous work it had been found that oxide of uranium in the 

 colloidal state gave a far greater effect than the crystalloidal salts, and the 

 inference was drawn that the state of aggregation of the colloid was favour- 

 able to the photo-synthetic reaction. Accordingly in our 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 eflFect is much greater than that obtained with an equal concentra- 

 tion 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 approach- 

 ing 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 freezing-point method, and the degree of ionisation 

 as given by conductivity determinations. . It is shown in the case of ferric 

 chloride solutions by the darkening in colour of dilute solutions on warming, 

 approaching the colour shown by colloidal iron solutions, and persisting after 

 the heated solution has cooled agaii], for prolonged periods of time. Also, if 

 a dilute solution of ferric chloride be boiled a precipitation of a part of the 

 iron as ferric oxide is obtained, and the precipitate remains permanent on 

 cooling although the period of boiling is far too short to remove a corre- 

 sponding amount of hydrochloric acid. All these facts demonstrate that there 



