92 ACTION OF LIGHT RAYS 



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 nitrate 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 ex- 

 posed 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 a reaction 

 was obtained of about 2 parts of formaldehyde per 1,000,000, show- 

 ing an amount of about 1 part in 20,000 in the original emulsion. 

 This result was not, however, due to the combined action of chloro- 

 phyll and colloidal ferric hydrate, for a similar intense result was 

 obtained when an exposure was made of an emulsion of chloro- 

 phyll extract alone in distilled water and without any carbon 

 dioxide. 



It follows that the formaldehyde must have originated either 

 from the chlorophyll or the other organic substances in the green 

 leaves taken out by the alcohol along with the chlorophyll. 



Additional experiments revealed the interesting fact that prac- 

 tically any complex organic substance of biological origin yields 

 formaldehyde when exposed to the action of ultra-violet light, and 

 also though more slowly when exposed to sunlight. Solutions 

 or emulsions were exposed of all the commoner sugars (such as 

 glucose, fructose, maltose, lactose, saccharose), of glycogen, starch, 

 glycerine, egg- albumen, milk, and various vegetable juices. After 

 three to four hours' exposure and subsequent filtration or distillation 

 these all showed the presence of formaldehyde in varying amount. 

 The more transparent solutions gave the more intense reactions, 

 and amongst these the sugars were most rapidly disrupted by the 

 action of the light. The action appears to be one of successive 

 hydrolysis ; thus, for example, cane sugar is first inverted, and after 

 an hour or two gives a strong reduction with Benedict's solution. 

 The reaction takes place also with sterilised sugar solutions, in 

 sealed glass tubes, exposed to bright sunlight, but the speed of 



