174 



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



13 days of bright sunshine. At the end of the period, 40 c.c. were withdrawn 

 and distilled. A very distinct positive reaction for formaldehyde was obtained 

 with Schryver's test. 



Experiment III. Exposure to Sunlight in Transparent Silica Flask. — A 

 colloidal solution of ferric hydroxide of a concentration of 014 per cent., 

 measuring 50 c.c, was placed in a silica flask through which carbon dioxide 

 was passed, on the roof. The experiment lasted for two days, of which the 

 first was dull, and the second almost continuous bright sunshine. On dis- 

 tillation this gave a most marked positive reaction with Schiffs test, 

 indicating from the short period of exposure that the reaction probably 

 proceeds more rapidly in silica vessels which are more transparent to the 

 shorter wave-lengths of light. 



Experiment IV. Exposure to Mercury Arc Lamp with Uviol Glass Shade. — 

 A colloidal solution of ferric hydroxide diluted 1 in 20 from a stock 

 solution of 2 - 26 per cent., and hence containing 0"113 per cent, of colloid, 

 was placed in a wide 1000 c.c. measuring cylinder. In this glass cylinder 

 was immersed a wide round-bottomed tube of " Uviol " glass of somewhat 

 smaller diameter to serve as a protector between the heated lamp to be 

 placed in the interior, and the surrounding fluid between the " Uviol " tube 

 and the outer cylinder of glass. The mercury lamp was then set going, and 

 inserted in the centre of the " Uviol " glass protecting tube. The mercury 

 lamp tube, also of " Uviol " glass, had a diameter of 3 cm. approximately, the 

 protecting tube a diameter of 5'4 cm. externally, and the outer glass cylinder 

 an internal diameter of about 6 - 2 cm. The light generated at a distance of 

 about 2 cm., after passing two thicknesses of " Uviol " glass and a layer of air 

 of somewhat less than a centimetre, passed through a layer of the colloidal 

 solution about 4 to 5 mm. thick and then reached the outer glass vessel. On 

 account of the rounded bottom of the " Uviol " protecting tube there was 

 a certain considerable volume of the solution at the bottom not so well 

 illuminated. The total volume of colloidal solution at the bottom and in the 

 annular space between the two tubes was approximately 300 c.c. 



A slow steady stream of washed carbon dioxide was passed through the 

 colloidal solution. 



After about half-an-hour's running the colloidal solution became too warm 

 and began to coagulate, so the current was switched off and the lamp allowed 

 to cool. The whole was then immersed in a wide square-sided glass jar of 

 about 17 litres capacity through which a stream of cold water was con- 

 tinuously circulated. The lamp was now re-lit and kept going for a period of 

 2 hours, making 2\ hours of illumination in all. In this first experiment 

 with the " Uviol " apparatus, the colloidal solution had coagulated at the end 



