1903.] Cy 'anagenesis in Plants. 287 



A modification of the method used by Fordos and Gelis* has, there- 

 fore, been used in the present instance. This consists in adding 

 volumetric iodine solution to the liquid containing hydrocyanic acid 

 until the whole of the latter has been converted into cyanogen iodide 

 according to the equation : 



The formation of cyanogen iodide is, however, quickly inhibited 

 by the accumulation in the liquid of hydriodic acid. The originators 

 of the process attempted to overcome this difficulty by first rendering 

 alkaline with potash the liquid to be titrated, and then adding water 

 aerated with carbon dioxide to convert any excess of alkali into the 

 acid carbonate. We have found, however, that it is easier to titrate 

 the hydrocyanic acid with iodine in presence of sodium hydrogen 

 carbonate than to titrate the alkali cyanide under these conditions, 

 and consequently we have modified the process by adding to the 

 liquid to be titrated excess of sodium hydrogen carbonate. As this 

 method of titration has rarely been used previously, we have confirmed 

 the results so obtained by gravimetric estimations of the amount of 

 hydrocyanic acid in the distillate. 



Hydrocyanic acid produced, 

 estimated by the modified 



Fordos "and Gt-elis Estimated as 



Colour of beans. method, per cent. silver cyanide. 



{JSS 



Light brown ...... 0-041 0'0503 



It thus appears that the beans with dark brown or purple markings 

 furnish more prussic acid than the beans with light brown markings, 

 and that the largest amount produced was equivalent to about one- 

 tenth per cent, calculated on the dry beans. 



Isolation and Determination of the Constitution of the Glucoside 

 Phaseolunatin. 



The finely powdered beans were exhausted by cold percolation with 

 purified methylated alcohol. The mixed alcoholic liquors were then 

 concentrated to a syrup, which was boiled repeatedly with water in 

 order to separate the glucoside from resin. Tannin, gum and extractive 

 matters were removed form the solution by precipitation with lead 

 acetate, the excess of the latter being subsequently eliminated as lead 



* ' Journ. de Chimie et de Pharmacie,' vol. 23, p. 48. 



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