CYANOGENESIS 157 



a Soxhlet extractor for twenty-four hours. The solvent is 

 then distilled off from the extract, a little water is added, 

 and then sufficient 10 per cent, sulphuric acid to bring 

 the concentration of the acid roughly to 6 per cent, the 

 total volume being about 50 c.c. The mixture is then 

 distilled until no more prussic acid is liberated, the end 

 of the condenser passing under the surface of dilute 

 caustic soda contained in the receiving flask. The 

 distillate is then titrated, according to Liebig's method, 

 with standard silver nitrate solution, (i c.c. = o-ooi 

 gram HCN.) 



2KCN + AgN03 = AgCN.KCN + KN03 



The water in the distilling flask is replenished from a 

 tap-funnel as required. 



{b) " Free " Prussic Acid. 



The prussic acid liberated when the finely ground 

 linseed cake or other feeding stuff is soaked with water 

 is estimated in the following manner : — About 250 c.c. 

 of water are placed in a round-bottomed long-neck 

 flask of about \\ litres capacity, a few drops of toluene 

 added, and the liquid brought to the experimental 

 temperature by immersion in a thermostat. A weighed 

 quantity of the finely ground cake, varying from 25 to 

 50 grams according to circumstances, is then introduced 

 into the flask, mixed by giving the contents a shake, 

 and the flask then stoppered with a rubber bung and 

 placed in the thermostat. If the water is added to the 

 cake, instead of vice versa, the material is apt to clog 

 and not become thoroughly wetted. 



When the action has ceased (twelve hours is sufficient 

 at a temperature of 38° C), the contents of the flask are 

 steam distilled into saturated sodium bicarbonate 

 solution and the prussic acid content of the distillate 



