This section is from the book "Meals Medicinal", by W. T. Fernie. Also available from Amazon: Meals Medicinal: With "Herbal Simples" Curative Foods From the Cook in Place of Drugs From the Chemist.
A Mustard poultice made with the farina of black Mustard seed, and water, (with, or without some wheaten flour added) into a paste, constitutes one of the most effectual external stimulating applications we can employ. It quickly induces a sharp burning sensation on the skin of the part, with redness, (which would presently go on to destructive inflammation of the cutaneous surface, implicating the true skin below more deeply than does the old-fashioned blister of Spanish fly); so that the sinapism, or Mustard poultice, has superseded the blister, because acting more promptly, and more energetically for the speedy relief of internal congestions. A poultice made entirely of Mustard-seed should not be kept applied longer than ten minutes at a time. The volatile oil of this Mustard-seed, when mixed with spirit of wine (twenty-four drops of the oil to each fluid ounce of spirit) makes a capital liniment for external use against the painful stiffness of chronic rheumatism, or for determining blood derivatively to the surface from deeper congested, or aching parts.
Against a headache for which prompt relief must be had, if a whole tin of Colman's Mustard is put into a large, hot bath, and the sufferer remains in the bath for ten or fifteen minutes, and lies down in the room for half an hour afterwards, the brain will then be far clearer for a while than even in ordinary health.