Through the agency of the myrosin, another constituent of brown seed, when the two are brought in contact through the medium of water, we have vegetable albumen, a bitter principle, a little gum and sugar, and a peculiar green substance, cellulose, and mineral water, called sulphocyanide of sinapine.[8] The aqueous extract of yellow mustard seed yields with a solution of ferric chloride a deep, blood-red coloration, which is scarcely perceptible with similar extract of black mustard. The aqueous extract of white mustard acquires a powerful odor of sulphurated hydrogen in a few hours, while that of the black seed smells only of the pungent mustard oil.
White mustard seed contains from 25 per cent. to 35 per cent. of an inodorous fixed oil with a little tendency to become rancid and of little pungency, which it will not give up in water. In place of myronic acid converted into volatile oil of mustard, it contains a non-volatile, bitter and acrid salt termed sulphocyanide of sinapine (C_{ 17}H_{ 24}N_{ 2}SO_{ 5} or C_{ 16}H_{ 23}NO_{ 5}CNHS), myrosin gum cellulose and mineral matter. Now, as it is on the volatile oil and the acrid and somewhat bitter salt that the pungency and acridity of mustard depend, we can see a strong reason why in the mustard of commerce the farina of the two species, black and white seed, should be blended together, in the proportion of two parts of white to one of black. The black seed does contain some of the acrid principle as well as the volatile oil, as has been verified by the action of nitric acid, caustic potash, and ferric chloride, on the alcoholic extract. It is, therefore, the most valuable of the two seeds on account of the little volatile oil in the yellow seed. The acrid principle of white mustard appears to possess but little stability, although it has been said to bear a temperature of 130 degrees C. We find that it is readily affected by heat and that it is not safe to evaporate the alcoholic solution containing it at a higher temperature than about 30 degrees C., for, if subjected to a much higher temperature, it quickly loses its acridity and acquires a bitter, caramel-like taste.
The oil extracted by ether from the brown seed is of a bright and beautiful emerald-green color, owing to the peculiar green principle described as one of its constituents. So deep and remarkable is the color of the oil that it would be easy by means of a graduated scale of tints to determine with very tolerable certainty the percentage of brown mustard contained in any sample of mixed mustard. Specific gravity, 1.017; boils at 148 degrees.