184 Journal of Agricultural Research voi. iv. No.a 



is developing most rapidly. Treub (12) and Ravenna and Zamorani (9) 

 are of the opinion that hydrocyanic acid is a necessary intermediate 

 product in the formation of proteins. As such, the quantity present at 

 any one time might be subject to such Variation as this experiment 

 shows. 



Further experiments will be carried on next season (191 5) to deter- 

 mine, if possible, just what effect variety and climatic conditions may 

 have on the prussic-acid content of sorghum, as well as the function of 

 the acid in the metabolism of the plant. 



METHOD OF DETERMINING HYDROCYANIC ACID 



For the determination of hydrocyanic acid the colorimetric method of 

 Francis and Connell (7) was used, with one important modification. It 

 was found that when the macerated tissue was distilled with sulphuric acid 

 according to their method the distillate became yellow, and when sub- 

 sequently treated with ferric chlorid a greenish or brownish precipitate 

 was formed which masked the color of the thiocyanate. Enzym hydro- 

 lysis was therefore resorted to. Slade (11) digested the ground tissue 

 for 12 hours at room temperature, making use of the enzym which is 

 always found in a plant in conjunction with a cyanogenetic glucosid. 

 But we found that at 40° to 45° C. complete hydrolysis was obtained in 

 two hours or less, as portions of the same sample gave the following 

 results : 



Time of digestion. HCN in lo gm. of ground material. 



2 hours o. 00040 gm. 



4 hours o. 00040 gm. 



6 hours o. 0002 5 gm. 



In all our work 2 -hour digestions were used, and the hydrocyanic 

 acid distilled and determined in the usual way. 



CONCLUSIONS 



The following points may be presented as a summary of these notes : 



(1) When sorghum is grown on poor, infertile soil, added nitrogen may 

 slightly increase the amount of hydrocyanic acid in the plant. "With 

 a fertile soil and abundant nitrogen this effect may not be produced. 



(2) During the first three or four weeks of the plant's life the prussic 

 acid is concentrated in the stalks. Then it rapidly decreases and dis- 

 appears there, but apparently persists in the leaves in decreasing per- 

 centages until maturity. 



(3) Climate and variety may be more important factors than soil 

 nitrogen in determining the amount of the acid in the plant. 



(4) Complete hydrolysis of the glucosid is obtained by digesting the 

 macerated tissue for two hours at 40° to 45° C. 



