EXTRACTS 323 



each, placed in a row without intervals, it was found that the detonation extended to 

 3 feet in about one five-thousandth part of a second.' 



EXPRESSED OILS. See OILS. 



EXTRACT OP XiEAD. A common name for the solution of acetate of lead, 

 also called Goulard's Lotion. 



EXTRACTS. (Extraits, Fr. ; Extracten, Ger.) The older apothecaries used this 

 term to designate the product of the evaporation of any vegetable juice, or infusion, 

 or decoction ; whether the latter two were made with water, alcohol, or ether ; whence 

 arose the distinction of aqueous, alcoholic, and etherous extracts. 



Fourcroy made many researches upon these preparations, and supposed that they 

 had all a common basis, which he called the extractive principle. But Chevreul and 

 other chemists have since proved that this pretended principle is a heterogeneous and 

 very variable compound. 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 watery extracts, which are those most com- 

 monly made, are as various as the vegetables which yield them ; some containing 

 chiefly sugar or gum in great abundance, and are therefore innocent or inert ; while 

 others contain very energetic impregnations. The conduct of the evaporating heat is 

 the capital point in the preparation of extracts. They should be always 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 100 or 120 Fahr. 

 Steam heat is now applied advantageously in some cases, where it is not likely to de- 

 compose any of the principles of the plant. But by far the best process for making 

 extracts is in vacuo, upon the principles explained in the article EVAPORATION. 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 maintain a good 

 vacuum under several receivers, placed upon the flat ground flanges of so many basins, 

 each provided with a stop-cock at its side for exhaustion. The airless basin contain- 

 ing 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 delicate purposes, the concentration may be performed in the cold, 

 by placing saucers filled with the expressed juice over a basin containing sulphuric 

 acid, putting a glass receiver over them, and exhausting its air. 



The use of the air-pump for evaporating such chemical substances as are readily 

 injured by heat, has been very common since Professor Leslie's discovery of the efficacy 

 of the combined influence of rarefied air and an absorbing surface of sulphuric acid in 

 evaporating water at low temperatures. It has been supposed that the virtues of 

 narcotic plants in particular might be better obtained and preserved by evaporation 

 in vacuo than otherwise, as the decomposing agency of heat and atmospheric oxygen 

 would be thereby excluded. There is no doubt that extracts thus made from the 

 expressed juices of fresh vegetables possess, for some time at least, the green aspect 

 and odour of the plants in far greater perfection than those usually made in the air, 

 with the aid of artificial heat. Dr. Meurer has endeavoured to show that the colour 

 and odour are of no use in determining the value of extracts of narcotics', that the 

 albumen left unchanged in the extracts made in vacuo, tends to cause their spontaneous 

 decomposition, and that the extracts made with the aid of alcohol, as is the practice in 

 Germany, are more efficacious at first, and much less apt to be injured by keeping. 

 M. Baldenius has detailed experiments to prove that the juices of recent plants mixed 

 with alcohol, in the homeopathic fashion, are very liable to spontaneous decomposition. 

 To the above expressed juice, the Germans add the alcoholic tincture of the residuary 

 vegetable matter, and evaporating both together, prepare very powerful extracts. 



Extracts of bark and other vegetable substances to be used in tanning or dyeing are 

 made in the countries in which the plants grow. The operation is very roughly per- 

 formed, and the imported extracts are usually very full of impurities. 



In 1872 we imported of Extracts unenumerated as follows, the values only being 

 given : 



Value 



From Belgium 5,265 



France 4,043 



United States of America . . . . 6,853 

 British North America .... 4,400 

 Other Countries . . . . . 1,253 



21,814 



Y2 



