EXTRACTS. The older apothecaries used this term to designate the product of the evaporation of any vegetable juice, infusion, or decoction ; whether the latter two were made with water, alcohol, or ether ; whence arose the distinction of aqueous, alcoholic, and ethereous extracts. made many researches upon these preparations, and supposed that they had all a common basis, which he called the extractive principle. But Cher reul and other chemists have since proved that this pretended principle is a heterogeneous and very variable com pound. By the term extract, therefore, is now meant merely the whole of the soluble matters obtained from vegetables, reduced by careful evaporation to either a pasty or solid consistence. The wa tery extracts, which are those most com monly made, are as various as the vege tables which yield them ; some contain ing chiefly sugar or gum in great abund ance, and are therefore innocent or inert ; while others contain very energetic im pregnations. The conduct of the evapo rating heat is the capital point in the pre paration of extracts. They should be al ways prepared, if possible, from the juice of the fresh plant, by subjecting its leaves or other succulent part, to the action of a powerful screw or hydraulic press ,• and the evaporation should be effected by the warmth of a water-bath, heated not beyond or 120° F. Steam heat
may perhaps be applied advantageously in some eases, where it is not likely to decompose any of the principles of the plant. But by far the best process for making extracts is in vacuo. It is much easier to fit up a proper apparatus of this kind, than most practical men imagine. The vacuum may either be made through the agency of steam, as there pointed out, or by means of an air-pump. One Powerful air-pump may form and main tarn a good vacuum under several re ceivers, placed upon the flat-ground flanges of so many basins, each provided with a stop-cock at its side for exhaus tion. The airless basin containing the juice being set on the shelf of a water bath, and exposed to a proper tempera ture, will furnish, in a short time, a large quantity of medicinal extract, possessing the properties of the plant unimpaired.
For exceedingly delicatepurposes, the concentration may be performed in the cold, byplacing saucers filled with the expressed juice over a basin containing sulphuric acid, putting a glass receiver over them, and exhausting its air.