DRAGON'S BLOOD DRAINING. 



719 



DRAGON'S BLOOD ; a resinous juice obtained 

 by incision from several different plants, found be- 

 tween the tropics ; from the trunk of the ptero- 

 earpus draco, a tree of the natural order leguminosae, 

 growing in the East Indies, which yields Oriental 

 dragon's blood ; from the pterocarpus santalinus, 

 inhabiting tropical America, which affords it in less 

 quantity and more impure ; from the calamus draco, 

 a palm of the East Indies, from which it is obtained, 

 according to Kampfer, by boiling the fruit ; from a 

 dalbergia in Guiana, and a croton in South America ; 

 from the dracana draco, the native country of which 

 is not known with certainty, but is supposed to be 

 Africa. A single tree of this last species, which 

 was introduced into the Canaries at the time of the 

 conquest, acquired enormous dimensions, and has 

 been visited and celebrated by every traveller, but 

 was destroyed by a storm, in 1822. 



Dragon's blood is obtained, in commerce, in three 

 principal forms in that of oval masses, of the size of 

 a pigeon's egg, enveloped with leaves of the pan- 

 danus ; in cylinders, covered with palm leaves ; and 

 in irregular masses, marked with impressions of 

 leaves : that in oval masses is the most esteemed. 

 It is cften very much adulterated, and other sub- 

 stances are substituted ; particularly gum Arabic 

 and gum Senegal, coloured with logwood, &c. Sev- 

 eral of these substances may be Detected by their 

 dissolving in water, while dragon's blood is nearly 

 insoluble; others require to be submitted to some 

 chemical tests. Madagascar furnishes this resin of 

 a good quality, but so much mixed with foreign sub- 

 stances, that it is little used. 



Dragon's blood is opaque, of a deep, reddish-brown 

 colour, brittle, and has a smooth and shining con- 

 choidal fracture ; when in thin laminae, it is sometimes 

 transparent ; when burnt, it gives out an odour some- 

 what analogous to benzoin ; its taste is a little astrin- 

 gent ; it is soluble in alcohol, and the solution will 

 permanently stain heated marble, for which purpose 

 it is often used, as well as for staining leather and 

 wood. It is also soluble in oil, and enters into the 

 composition of a very brilliant varnish, which is much 

 esteemed by artists. Its quality may be proved by 

 making marks on paper : the best leaves a fine red 

 trace, and commands a pretty high price. It was 

 formerly in high repute as a medicine, but at the 

 present time is very little used. An astringent resin, 

 obtained from the eucalyptus resinifera of New Hol- 

 land, bears the name of dragon's blood in the settle- 

 ments in that country. . 



DRAGON-SHELL, in natural history, a name 

 given to a species of concamerated patella or limpet. 

 It has a top very much bent, and is of an ash-colour 

 on the outside, but of an elegant and bright flesh 

 colour within. It has been found sticking to the 

 back of a tortoise, as the common limpets do to the 

 sides of rocks, and some have been affixed to large 

 shells of the pinna marina. 



DRAGOON ; a kind of light-horseman, of French 

 origin, trained to fight either in or out of the line, 

 in a body or singly, chiefly on horseback, but, if ne- 

 cessary, on foot also. The dragoons were mounted, 

 armed, and exercised as these objects require. They 

 probably took the name of dragoons from the Roman 

 draconarii, whose lances were adorned with figures 

 Of dragons. Experience proving that they did not 

 answer the end designed, they were hardly ever used 

 in infantry service, and now form a useful kind of 

 cavalry, mounted on horses too heavy for the hussars, 

 and i; light for the cuirassiers. 



DRAINING, in agriculture ; a method of improv- 

 ing the soil by withdrawing the water from it. 

 Though practised by the Romans, it was not till 

 after the middle of the last century that the impor- 



tance of draining began to be fully understood in 

 Britain. The public attention is said to have been 

 first excited by the practice of Elkington, a farmer 

 and self-taught professor of the art of draining in 

 Warwickshire and the adjoining counties. On the 

 practice of this artist most of the future improve- 

 ments are founded ; and they have been ably em- 

 bodied in the account of his practice by Johnston. 

 (Edinburgh, 1797, 4to, subsequent editions in 8vo.) 



The successful practice of draining in a great mea- 

 sure depends on a proper knowledge of the various 

 strata of which the earth is composed, as well as of 

 their relative degrees of porosity, or capability of 

 admitting or rejecting the passage of water through 

 them, and likewise of the modes in which water is 

 formed, and conducted from the high or hilly situa- 

 tions to the low or level grounds. In whatever way 

 the hills or elevations that present themselves on the 

 surface of the globe were originally formed, it has 

 been clearly shown, by sinking large pits, and dig- 

 ging into them, that they are mostly composed of ma- 

 terials lying in a stratified order, and in oblique or 

 slanting directions downwards. Some of these strata, 

 from their nature and properties, are capable of ad- 

 mitting water to percolate or pass through them ; 

 while others do not allow it any passage, but force it 

 to run or filtrate along their surfaces without pene- 

 trating them in any degree, and in that way conduct 

 it to the more level grounds below. There it be- 

 comes obstructed, or dammed up by meeting with 

 impervious materials of some kind or other, by 

 which it is .readily forced up into the superincum- 

 bent layers, where they happen to be open and porous, 

 soon rendering them too wet for the purposes of agri- 

 culture ; but where they are of a more tenacious and 

 impenetrable quality, they only become gradually 

 softened by the stagnant water below them; by 

 which the surface of the ground is, however, ren- 

 dered equally moist and swampy, though somewhat 

 more slowly than in the former case. It may also 

 be observed, that some of the strata which constitute 

 such hilly or mountainous tracts are found to be con- 

 tinued with much greater regularity than others ; 

 those which are placed nearest to the surface, at the 

 inferior parts of such hills or elevations, being- mostly 

 broken or interrupted before they reach the tops 

 or higher parts of them ; wliile those which lie deeper, 

 or below them at the bottom, show themselves in 

 these elevated situations. Thus, that stratum which 

 may lie the third or fourth, or still deeper, at the 

 commencement of the valley, may form the upper- 

 most layer on the summits of hills or mountainous 

 elevations. 



Where grounds are in a great measure flat, and 

 without such degrees of elevation as may be sufficient 

 to permit those over-proportions of moisture that may 

 have come upon them, from the higher and more ele- 

 vated grounds, to pass readily away and be carried 

 off. and where the soils of the land are composed or 

 constituted of such materials as are liable to admit 

 and retain the excesses of moisture ; they are exposed 

 to much injury and inconvenience from the retention 

 and stagnation of water. Such lands consequently 

 require artificial means to drain and render them 

 capable of affording good crops, whether of grain 

 or grass. 



To perform properly the business of draining, at- 

 tention should not only be paid to the discrimination 

 of the differences in regard to the situation of the 

 lands, or what is commonly denominated drainage 

 level ; but also to the nature, distribution, and 

 depth of the* materials that constitute the soils, 

 or more superficial parts of them ; as upon each of 

 these some variety, in respect to the effects arising 

 from water retained in them, may depend. The 



