1 86 GLUCOSIDES 



Preparation. 



Green gives the following method for its extraction : One 

 kilogram of the seeds of the black mustard is ground to a 

 fine powder, and then extracted with one and a half litres of 

 82 per cent alcohol. The mixture is heated on a water bath 

 until the volume of the alcohol is reduced by about one-sixth, 

 the alcoholic extract is then filtered off, and the residue pressed 

 while it is still hot. The operation is then repeated ; the 

 residue is dried at 1 00 C, and digested for twelve hours with 

 eight times its volume of cold water. A small quantity of 

 barium carbonate is added to this aqueous extract, which is 

 then evaporated to a syrup. The sinigrin is contained in this 

 syrup, and is extracted by boiling with 82 per cent alcohol. 

 Finally, the alcoholic extract is evaporated down, when the 

 glucoside crystallizes out in rhombic prisms, which are freely 

 soluble in water and warm alcohol, but much less soluble in 

 cold. 



Sinigrin is split by the enzyme myrosin into glucose, 

 potassium hydrogen sulphate and allyl isothiocyanate, or 



mustard oil, which may be recognized by its distinctive smell. 



" 



4 



KHSO 4 + CH 2 : CHCH 2 NCS 



CONIFERIN. 



This glucoside occurs in various coniferous trees, especially 

 in young parenchyma, and also in asparagus. With concen- 

 trated sulphuric acid coniferin gives a violet coloration, while 

 hydrochloric acid and phenol give a blue coloration. Most 

 reagents used in the demonstration of the lignification of cell 

 walls (p. 164) give similar reactions both with coniferin and 

 vanillin, and for this reason it is supposed that both these 

 substances occur in such thickened walls. By using a mixture 

 of thallin sulphate (which stains vanillin yellow) with thymol 

 (which with coniferin and concentrated hydrochloric acid gives 

 a blue colour), it has been shown that coniferin is more 

 abundant in young wood cells, whilst vanillin occurs more 

 extensively in the older elements. 



Such colour reactions must, however, be used with caution 

 since they mostly depend on the presence of some complex 



