i88 GLUCOSIDES 



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

 residue is dried at ioo° 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. 

 C,oH,gO,oNKS2 = C6Hi.,06 + KHSO4 + CH^: CHCHjNCS 



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. In brief, 

 most reagents used in the demonstration of the lignification of 

 cell walls (p. 145) give similar reactions both with coniferin and 

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

 substances occur in such thickened walls. The use of these 

 reagents tends to show that coniferin is more abundant in young 

 wood cells, whilst vanillin, which is coloured yellow by thallin, 

 occurs more extensively in the older elements. All such colour 

 reactions, however, must be used with caution since many of 

 them depend on the presence of certain complexes, e.g. alde- 

 hyde, which may occur in the molecules of widely different 

 substances. 



Coniferin crystallizes in needle-shaped crystals, m.p. 185°, 

 and is soluble in warm water and warm alcohol. On hydrolysis 

 by mineral acids or by emulsin it gives glucose and coniferyl 

 alcohol : — 



CieHoA + H,0 = C^HiaOc + CjoHj^O, 



Coniferin Coniferyi 



alcohol 



The latter is a crystalline substance melting at 73°. 



Both coniferin and coniferyl alcohol when oxidized with 



