46 SYNTHESIS BY SUNLIGHT IN KELATIONSHIP 



dimensions ; in the first were placed 20 c.c. of distilled water saturated 

 with carbon dioxide from a " sparklet " syphon, and 2 c.c. of stock 

 colloidal uranium hydroxide solution; in the other tube, 20 c.c. of 

 the water charged with carbon dioxide from the same syphon and 

 0-2 c.c. of 20 per cent, crystalloidal uranium nitrate solution. At 

 the end of the experiment, by drying and incinerating a measured 

 volume, the percentage of uranic oxide was determined, and it 

 was found that the colloidal solution contained 0-041 per cent., and 

 the crystalloidal 0-08 per cent., so that the crystalloidal solution 

 was approximately double in concentration that of the colloidal. 

 The two tubes were hermetically sealed and placed on the roof for 

 six days, three of which had bright sunshine, the others very cloudy 

 and raining. The two tubes were opened, and the contents separ- 

 ately distilled in a similar fashion. The distillate from the crys- 

 talloid showed negative results with the SchifPs test, while the 

 distillate from the colloid gave a most strongly marked positive 

 reaction. 



Experiment V.: Illustrating the Necessity for Strong Direct Sun- 

 light. Two solutions, one of colloidal uranic oxide, the other crys- 

 talloidal uranium nitrate of approximately equal concentration, 

 were taken, of each 50 c.c., in a glass tube, and washed carbon dioxide 

 was bubbled through each in a slow stream. These were exposed 

 on the roof for two days. Both these days were dull with practically 

 no sunshine; there was, however, fairly bright diffuse daylight. 

 The contents were then distilled as in the preceding experiments, 

 but negative results were obtained in both cases. 



Experiment VI. Four similar wide glass tubes were taken, and 

 into each was introduced 30 c.c. of distilled water charged pre- 

 viously with carbon dioxide, and 2 c.c. of colloidal uranic oxide 

 solution, containing 0-478 per cent, of Ur 2 3 . Accordingly, the 

 concentration of colloid in each case was approximately 0-03 per 

 cent., or 3 in 10,000 parts. The four glass tubes were then sealed 

 up hermetically and treated as follows : 



1. The first tube was exposed on the roof to such sunlight as was 

 available for six days, in four of which there was brilliant sunshine 

 all day. 



2. The second tube was preserved for the same period in a dark 

 cupboard in the laboratory. 



3. The third tube was immersed in a wider open glass tube con- 

 taining a strong alcoholic solution of chlorophyll, so as to give a 



