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



crystalloidal uranium nitrate alongside, and given the same exposure and 

 general conditions, we have been able to show that the colloidal condition is- 

 much more active in this photo-chemical reaction. In this comparative 

 experiment the crystalloidal uranium nitrate was precipitated while no 

 precipitation whatever occurred in the colloidal uranic hydroxide. 



Passing on, we have shown that similar photo-synthesis of organic from 

 inorganic matter easily occurs with colloidal ferric hydroxide, and by the 

 use of the " Uviol " mercury lamp we are enabled to experiment at all times 

 and obtain synthetic results readily in a few hours, a consideration of some 

 importance in working in a country where sunlight is so variable, and so 

 often unavailable for days. 



The experiments with uranic hydroxide and ferric hydroxide were made- 

 concurrently in time, but for convenience we shall describe first the uranium 

 experiments and then those with the ferric hydroxide. 



Photo- synthesis by Colloidal Uranic Hydroxide. 



Method of Preparation of the Colloidal Solution. — A strong solution of 

 uranium nitrate (approximately 10 per cent.) is taken and treated in the 

 cold by adding a saturated solution of ammonium carbonate until the 

 precipitate just ceases to re-dissolve. The solution is then filtered and 

 dialysed in a tube of parchment paper for several days against running water. 

 The greater part of the uranium is still in the crystalloidal state, and dialyses- 

 away at this stage. Great care is required in the first step to get the proper 

 relative amount of ammonium carbonate ; also it is as well not to wait for 

 the removal of the last traces of crystalloidal uranium, but to take the 

 solution when it still gives a faint reaction with potassium ferrocyanide. 

 The amount so left is, however, very minimal compared with the crystalloidal 

 uranium solutions as used in the experiments recorded below, and nearly all 

 the uranium at the end is present as colloidal uranic hydroxide. 



This method is practically the same as that described by Graham for the 

 preparation of colloidal ferric hydroxide and as used in the preparation of 

 our colloidal iron solutions. 



The amount of uranium in this solution was determined by evaporating a 

 measured volume to dryness and weighing the residue, and was found to be 

 0-478 per cent, of Ur 2 3 . 



In carrying out the photo-synthetic experiments this solution was either 

 diluted 15- to 20-fold with distilled water and carbon dioxide, evolved from 

 marble and pure hydrochloric acid and washed by water in a wash-bottle,, 

 passed through in a slow stream, or it was diluted to the same degree with 

 distilled water previously saturated with carbon dioxide and sealed up. 



