This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Pearl barley consists of the grains of common barley, or fruit of Hordeum vulgare and H. distichon, deprived of their exterior coating, and smoothed and polished in a mill. They are small oval bodies about a line in length, with a longitudinal mark on one side, smooth, and white. Pearl barley contains a large proportion of starch, with a little gum and sugar, which it yields to boiling water.
The decoction of barley, or barley-water, as it is commonly called, is very much used, as a bland, demulcent, and sufficiently nutritive drink, in febrile and inflammatory diseases, and fully deserves its reputation. Some care is requisite, in its preparation, to guard against mustiness, or other source of unpleasant taste, or irritant effect; as its chief merit depends upon its being acceptable to the palate and stomach.
The officinal Decoction (Decoctum Hordei, U. S., Br.) is prepared by taking two troyounces of pearl barley, washing it well with cold water, which is to be thrown away, then boiling it for a little while with half a pint of water, which also is to be thrown away; and lastly boiling the grains thus purified with four pints of water down to two. Every physician should be familiar with this process, so as to be able to give proper instruction to nurses. it may be flavoured with sugar, etc., if desired.
A Compound Decoction (Decoctum Hordei Compositum, Lond.; Mistura Hordei, Ed.) was formerly prepared by adding to the two pints of simple decoction prepared as above, two ounces of figs, half an ounce of bruised liquorice root, two ounces of stoned raisins, and a pint of water, then boiling to two pints, and straining. The decoction was thus rendered more nutritive, more demulcent, and more agreeable to the taste; but could not be given so freely in a very delicate condition of the stomach. it is not at present officinal.