180 



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



Exposed formaldehyde solutions turn yellow when concentrated by 

 distillation either at atmospheric or reduced pressure and leave behind a 

 yellow syrup with a bitter taste which strongly reduces Benedict's solution ; 

 unexposed formaldehyde solutions leave a smaller residue of white 

 paraldehyde. 



Experiment 9. — The condensing action of light is aided by slight alkalinity. 

 Three quartz test-tubes were taken : in the first was placed a mixture of 

 equal volumes of 4-per-cent. formaldehyde solution and water, in the second 

 and third a mixture of equal volumes of 4-per-cent. formaldehyde solution 

 and of a 1-per-cent. solution of sodium carbonate (Na2C03). The first and 

 second were exposed for three hours at a distance of 3 cm., while the third 

 was kept in -darkness in an incubator at approximately the same temperature 

 as that caused by the irradiation, viz., about 50° C. At the end of the period 

 the unexposed solution gave no reduction with Benedict's solution, and the 

 tube contents exposed in presence of the alkaline carbonate gave practically 

 double the intensity of reduction of those equally diluted with water. Tested 

 again at the end of 15 hours the contents of the tube kept warm in darkness 

 still gave no reduction, while the other two now gave each a heavy reduction. 

 Even after an additional period of three days in the incubator the dilute 

 formaldehyde and sodium carbonate solutions kept in darkness gave no 

 reduction with Benedict's solution. 



C. The General Formation of Formaldehyde hy tlie Action of Light upon 

 Organic Substances of Bio-chemical Origin. 



The series of experiments leading to the generalisation made in this section 

 were induced by an attempt to construct an emulsion of chlorophyll in 

 extractives from green leaves along with colloidal ferric hydrate so as to 

 produce an artificial system resembling that present in the chloroplast of the 

 green plant, which might then be exposed to light and tested for production 

 of formaldehyde. For this purpose a quantity of grass leaves was washed 

 with water and then extracted with absolute alcohol. The filtrate was 

 allowed to remain at room temperature in a desiccator over sulphuric acid 

 until the alcohol had evaporated and a green extract remained behind. This 

 was rubbed up and shaken into an emulsion with a colloidal solution of ferric 

 oxide. This emulsion was saturated with carbon dioxide and exposed for 

 about four hours to the light of the quartz mercury vapour lamp. At the 

 end the chlorophyll had bleached, and the ferric hydrate had coagulated so 

 that the whole could be filtered. The result was surprising as to the intensity 

 of the formaldehyde return ; when the Schryver test was applied there was 

 at once a deep pink colour produced. Even after a twenty-five-fold dilution 



