ON ELECTROMOTIVE PHENOMENA IN PLANTS. 



285 



VI. A New Method for the Quantitative Estimation of Hydrocyanic 



Acid. 



The most important progress made during the past year has con- 

 sisted in the elaboration of the method for the quantitative estimation of 

 small amounts of HON — i.e., less than 1 milligramme. 1 A colorimetric 

 method has been worked out by means of which it has been found 

 possible to estimate in thousandths of a milligramme the evolution of 

 HON by a single laurel leaf during short periods of time — by the day 



Fig. 3. 



-Apparatus for the distillation and subsequent estimation of luiimtt 

 quantities of HON in a vegetable or animal tissue. 



or hour at ordinary temperatures, by the minute at a temperature of 

 40°. Fig. 3 gives a curve of HON evolution taken at 40° in periods 

 of five minutes. Pig. 4 of the same, taken on two individual leaves at 

 one minute periods, with the specific purpose of determining as nearly 

 as might be the time lost between the moment of immersion and the 

 first appearance of HON. In the two cases examined this first appear- 

 ance took place during the fourth and during the fifth minute of 

 anaesthesia. Under similar conditions the electrical response dis- 

 appeared during the third and fourth minute. 



The procedure consists in matching with a colour scale containing 

 known amounts of hydrocyanic acid in picrate of soda the colour of 



1 Waller, ' A New Method for thj Quantitative Estimation of Hydrocyanic Acid 

 in Vegetable and Animal Tissues,' Proc. Physicl. Soc, June 18, 1910 ; Proc. Royal Soc., 

 June 20. 1910. 



1910. U 



