Synthesis by Sunlight in Relationship to the Origin of Life. \ 69 



hermetically in glass tubes, which were then exposed to such direct sunlight 

 as was available on the flat roof of the laboratory. 



It will accordingly be observed that the concentration of the colloidal 

 uranic hydroxide in the solutions actually exposed to the light was only 

 - 024 to 0'035 per cent. The stock solution of the colloid had a pale lemon 

 yellow colour, and the diluted solutions were almost colourless, showing just 

 the merest trace of yellow colour, and the solutions throughout remained 

 water clear. The colloidal solution is very sensitive, and is precipitated by 

 traces of added crystalloid. 



The test solution for aldehyde used in our earlier experiments was Schiff's 

 reagent, which consists of a dilute solution of fuchsin (about 1 per cent, in 

 water) through which sulphur dioxide is passed until it is just decolorised. 

 This reagent added in the proportion of 3 drops to 10 c.c. of a dilute 

 formaldehyde solution shows the presence of the latter by a distinct pink 

 coloration, developing in about half an hour at a dilution of 1 in 500,000. 



At a later stage our observations were confirmed by the Mulliken and 

 Schryver tests. 



Mulliken's test, as used by us, consists in adding two drops of a 3-per-cent. 

 solution of gallic acid in absolute alcohol to 6 c.c. of strong sulphuric acid 

 in a test-tube, and then pouring on the surface of this mixture 2 c.c. 

 of the solution suspected to contain formaldehyde, when a light blue 

 coloured ring develops at the junction and gradually penetrates the sulphuric 

 acid. 



Schryver's test was carried out by preparing- a 5-per-cent. solution of 

 potassium ferricyanide and a 1-per-cent. solution of phenylhydrazine hydro- 

 chloride which was used as follows : — To 10 c.c. of the solution suspected of 

 containing formaldehyde 2 c.c. of the phenylhydrazine solution is added, 

 then 1 c.c. of the potassium ferricyanide solution followed by 3 c.c. of 

 concentrated hydrochloric acid, when a pink coloration appears. If this is 

 diluted with water it becomes colourless, this colourless solution is shaken 

 with ether, and the ethereal solution which is not coloured is separated 

 off. Finally the ethereal solution is shaken up with a few cubic centimetres 

 of concentrated hydrochloric acid, when, if formaldehyde be present, a strong 

 pink or carmine colour appears in the hydrochloric acid layer. 



All three of these colour tests for formaldehyde have been obtained on 

 many occasions. 



Experiment I. — 20 c.c. of dilute colloidal uranic hydroxide solution contain- 

 ing approximately 0*03 per cent, of Ur 2 3 was placed in a test-tube on the 

 roof, and carbon dioxide generated in a Kipp, and washed as above described, 

 was slowly bubbled through. The day was a bright sunny one (May 26, 



vol. lxxxvii. — b. n 



