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"Brassica." The black is distinguished from the white by being nearly 
smooth. The pod too is very different, being destitute of the long 
flattened beak. 
The seeds contain three most important constituents: — a fixed oil, 
myrosin, and myronate of potassium. When the seeds are subjected to 
pressure they yield about 23 per cent, of a yellowish brown oil which does 
not easily turn rancid. Generally the oil is obtained from the dressings. 
Myrosin is a nitrogenous ferment, and performs the part in mustard that 
synaptaso does in the almond. Like albumen, myrosin is coagulatedjby 
heat. The myronate of potassium is a crystalline substance soluble in 
water. About 90 grains may be obtained from 2 lbs of seed. Now when 
myronate of potassium is mixed with the myrosin and water added, the 
essential oil of mustard is instantly developed. We can now readily 
understand the changes that take place when table-mustard or a poultice is 
prepared. The water dissolves the myrosin, sets it at liberty to act upon 
the myronate of potassium, and from its decomposition the essential oil is 
formed. Acids, alcohol, and heat retard this change, so that the popular 
notion of preparing mustard for the table or a poultice is a great mistake. 
Cold or slightly warm water and time are the true and scientific means. 
When making the French preparation with vinegar, the oil should firstbe 
developed with cold water and then the vinegar added, because when the 
oil is once formed acids do not alter its properties. 
Black mustard was formerly cultivated very extensively near Durham, 
where the manufacturers in 1720 gained great fame, in consequence of 
having found out a method of separating the dark coloured husk from the 
mterior of the seed. It is still grown in Yorkshire, Essex, and 
Cambridgeshire. The seed is sown in March and the plants gathered in 
September, In a good year an acre of land will produce between 24 and 
28 bushels of seed, the price ranging from ten to twenty sh illin gs per 
bushel. It is a very exhausting crop and requires a very rich soil. 
The white mustard (Sinapis alba Linn.) is found in the same locality 
but in greater abundance than the black. It is easily known by the 
pmnatifid leaves and differently shaped pods. The most singular 
difference however is in its chemical composition. It contains the fixed 
oil and myrosin, but no myronate of potassium, and therefore cannot in 
any way produce the essential oil and consequently the pungency which we 
like with our roast beef. The myrosin or fermentative substance is 
however much more abundant in the white, and this is the reason why a 
mixture of the white and black seeds is better for dietetic use than the 
