170 



Dr. B. Moore and Mr. T. A. Webster. 



1913) and the experiment was continued all day. Half of the solution was 

 taken out, and of this the greater part was distilled off from the colloid. Tested 

 with Schiffs reagent this distillate gave a distinct pink coloration within 

 half an hour. The remaining half of the colloidal solution was kept on the 

 following day, which was also a bright sunny day, on the roof with carbon 

 dioxide bubbling slowly through it, it was then tested in the same way 

 for aldehyde, and gave a still stronger reaction. Blanks were carried out 

 with distilled water and the Schiffs reagent and the contrast was most 

 marked, the distillate from the colloid exposed to light giving a deep pink, 

 while the distilled water control remained colourless. 



Experiment II. — Thirty c.c. of the same dilute colloidal uranium solution was 

 taken in a wide test-tube, saturated with carbon dioxide by bubbling the 

 gas through, and then hermetically sealed. The tube was left resting on 

 its side on the roof for two days, both of which had a good deal of bright 

 sunshine. The contents of the tube showed no visible alteration or precipi- 

 tation at the end of the period. The tube was now opened and about two- 

 thirds of its contents were distilled off. The distillate tested with Schiffs 

 reagent gives a marked formaldehyde reaction. 



Experiment III. — A soda-water syphon with a " sparklet " apparatus for 

 charging with CO2 was taken, and in it were placed 500 c.c. of distilled water, 

 30 c.c. of the stock colloidal uranium hydroxide solution, giving accordingly 

 a concentration of - 035 per cent, of Ur 2 3 . 



This was charged with carbon dioxide from a " sparklet " bulb, and left 

 on the roof for 13 days, of which 7 were bright days with strong sunlight. 

 At the end of the period a portion was withdrawn and distilled. It gave 

 strong positive reactions for formaldehyde with both Schiffs reagent and 

 Schryver's test. 



The stock solution of colloidal uranium hydroxide diluted equally and 

 distilled without previous exposure to light gave negative results in both 

 tests. 



Experiment I V. Contrast of Action of Colloidal Uranium and Crystalloidal 

 Uranium. — Two glass tubes were taken of similar 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 - 041 per cent., and the 

 crystalloidal - 08 per cent., so that the crystalloidal solution was approxi- 



