26o GLUCOSIDES 



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. 



PHASEOLUNATIN OR LINAMARIN. 



Phaseolunatin, C10H17O6N, occurs in the seeds of wild 



plants of Phaseolus lunatus (Burmah bean) ; it is present 



only in very small quantities, or is entirely absent from the 



seeds of the cultivated plants. It is also present in Linum, 



more especially that grown in tropical climates, and many 



rubber-yielding plants, such as Hevea hraziliensis and species 



of Manihot. Associated with it in its natural surroundings is 



the enzyme phaseolunatase which is able to hydrolyse it to 



acetone, glucose, and hydrocyanic acid,* from which it follows 



that phaseolunatin is a glucose ether of acetone cyanhydrin of 



the formula — 



CH«\ 



\C^_0— CH . {CHOH)3— CH . CH2OH 



CH3/ \CN I o ^ 



* Dunstan, Henry, and Auld : " Proc. Roy. Soc." B., 1906. 78, 145, 

 152. 



