CYANOGENETIC GLUCOSIDES 175 



been ascertained. In this connection attention may be drawn 

 to observations by Greshoff,* who states that the absence of 

 hydrocyanic acid does not necessarily indicate the absence of 

 a cyanogenetic glucoside. If the glucoside produced be very 

 small in amount, as in the case of Xeranthemum, the hydro- 

 cyanic acid may be used up directly it is formed, so that 

 benzaldehyde only will be found as a decomposition product. 



ISOLATION OF CYANOGENETIC GLUCOSIDES. 



Dunstan and Henry give the following method for the 

 isolation of dhurrin from Sorghum vulgare. The plants are 

 dried at a low temperature and ground up as finely as possible. 

 The material so obtained is extracted with alcohol and filtered ; 

 the alcohol is then distilled off from the filtrate and the residue 

 dissolved as completely as possible in warm water. Lead 

 acetate is added to this aqueous solution until no more pre- 

 cipitate (chiefly lead tannate) comes down. A current of 

 sulphuretted hydrogen a large excess is to be avoided is 

 then passed through the filtrate and the lead sulphide filtered 

 off. The excess of sulphuretted hydrogen can be removed 

 from the filtrate by passing through it a current of air. The 

 liquid is then worked up with pure animal charcoal, sufficient 

 in amount to convert the whole, when dry, into a powder, and 

 dried in a vacuum desiccator. When quite dry the material is 

 extracted with anhydrous ethyl acetate in a Soxhlet apparatus ; 

 this solvent slowly removes the glucoside, leaving most of the 

 sugar and other impurities behind. On distilling off the solvent 

 a syrup remains which may, if necessary, be again treated in 

 the same fashion. The syrup will deposit crystals of the 

 glucoside after standing for a few days in a vacuum over 

 sulphuric acid. The crystals so obtained may be recrystallized 

 from hot alcohol or boiling water. 



CHEMISTRY OF CYANOGENETIC GLUCOSIDES. 



We may now pass on to a brief consideration of the chemi- 

 cal nature of the cyanogenetic glucosides. These glucosides 

 vary in different plants. Thus comparing the cherry laurel, 

 Prunus Laurocerasus, with Pangium edule, it has been found 



*Greshoff; "British ASSOQ, Rep,, York," 1906, 138; " Kew Bull.," 1909, 

 397. 



