BLACK MUSTARD 147 



sufficient myrosin to decompose the whole of the sinigrin has been 

 shown to be incorrect. 



Sinigrin (also called potassium^ myronate), C 10 H 18 NS 2 O 10 K, may 

 be crystallised from either alcohol or water. It may be extracted 

 by first boiling the powdered seeds (not previously defatted) for a 

 short time with 80 per cent, alcohol, by which the activity of the 

 myrosin is destroyed ; from the pressed and dried seeds cold water 

 then extracts the sinigrin, which may be obtained by evaporating the 

 aqueous solution in the presence of barium carbonate, extracting with 

 alcohol, concentrating and crystallising (yield about 0-6 per cent.). 



Sinigrin, when submitted to the action of myrosin in aqueous 

 solution, decomposes into alryl isothiocyanate, acid potassium sulphate, 

 and dextrose : 



C JS^NSAoK = C 3 H 5 NCS + KHS0 4 + C 6 H 12 6 . 



Sinigrin Allyl isothiocyanate Acid pot. Dextrose 



sulph. 



This reaction, however, does not take place in the seed, as the 

 myrosin and sinigrin are stored up in separate cells. 



Allyl isothiocyanate, or volatile oil of mustard, is a mobile volatile 

 liquid with an extremely pungent taste and odour, and is the body 

 to which the pungent taste and odour of black mustard seeds (after 

 crushing and moistening with water) are due. The power of the 

 myrosin to effect this decomposition is destroyed by boiling water, 

 and therefore the seeds that have been subjected to such treatment 

 do not develop allyl isothiocyanate when treated with cold water. 



The cake that is left after the fixed oil has been expressed from 

 the seed contains both the sinigrin and the myrosin. From this cake 

 volatile oil of mustard may be prepared by crushing, macerating in 

 water for several hours, and distilling ; a mobile liquid collects at the 

 bottom of the distillate, and this, after redistillation, constitutes vola- 

 tile oil of mustard. It consists of allyl isothiocyanate, associated with 

 small quantities of other bodies such as allyl cyanide, C 3 H 5 CN, &c. 



Allyl isothiocyanate can also be produced artificially by decom- 

 posing allyl iodide with potassium thiocyanate ; allyl thiocyanate 

 (C 3 H 5 S.C:N) is formed, which on distillation is converted into the 

 isomeric, pungent allyl isothiocyanate, C 3 H 5 N:C:S (allyl thiocarbimide) 



I = II 



S C 3 H 5 N C 3 H 5 . 



The seeds yield about 0-7 to 1-3 per cent, of volatile oil, Dutch seeds 

 being the best. Official volatile oil of mustard (s.g., 1-014 to 1-025, 

 distils at 148-156) contains at least 92 per cent, of allyl isothio- 

 cyanate. 



Many Cruciferous plants, and some belonging to other natural 

 orders, yield under similar conditions a pungent volatile oil, thus 



