VEGETABLE PRODUCTS. 



147 



water, most of them are souble in alcohol, and 

 some of them in the fixed oils. When exposed 

 to heat they melt and afterwards take fire, burn- 

 ing with a strong yellow flame, and evolving a 

 great deal of smoke. Their elementary consti- 

 tution consists of carbon, hydrogen, and oxygen. 



Resin, or Rosin. Tliis substance exudes in i 

 the form of drops or tears, from the various 

 species of pines. Its flow is generally aided by 

 means of incisions into the bark and wood, 

 and it receives different appellations according 

 to the species from which it is obtained. If it is 

 obtained from the pinus si/lvestris, it is denom- 

 inated common turpentine; from pimis larix 

 Venice turpentine; or from amyris balsamea, 

 Canada balsam. It originally consists of two 

 ingredients, oil of turpentine and rosin. The 

 oil is extracted by distillation, and the resin re- 

 mains behind. If the distillation is continued 

 to dryness, the residuum is common rosin, or 

 colophonium; but if water is mixed with it while 

 yet fluid and incorporated by violent agitation, 

 the residuum is yellow rosin. The yellow rosin 

 is the most ductile, and the most generally used 

 in the arts. Oil of turpentine begins to boil at 

 313° of the thermometer; but if the ebullition 

 be still farther continued, the temperature rises 

 to 350°, or even higher, showing the presence of 

 more than one volatile oil. 



From the resinous juices of the fir, the sub- 

 stances known by the name of pitch and tar 

 are also manufactured. The trunk is cut or cleft 

 into pieces of a convenient size, which are pUed 

 together in heaps, and covered with turf. They 

 are then set on fire, and the resinous juice which 

 is thus extricated, being prevented from escaping 

 in a volatile state by means of the turf, is pre- 

 cipitated and collected in a vessel beneath. It 

 is partly converted into an empyreumatic oil, 

 and is now tar, which by being farther inspis- 

 sated, is turned into pitch. 



Mastic. This resin is extracted from the pis- 

 tacea kntiscus, a tree which grows plentifully in 

 the island of Chios. It exudes in a fluid state 

 from incisions made in the stem, and concretes 

 into brittle grains, somewhat yellowish and 

 semi-transparent. In this state it is sold under 

 the name of mastic. It has scarcely any taste; 

 out when heated it melts and exhales a fragrant 

 odour. It is sometimes employed as a varnish. 



Sandarac. This resin is obtained from the 

 juniperus communis, or common juniper, by 

 spontaneous exudations. It concretes in the 

 form of small round tears, somewhat brownish 

 and semi-transparent, resembling mastic. It is 

 also employed as a varnish. 



Elemi. Tliis resin is extracted from the 

 amyris elemifera, a tree which grows in North 

 America. It exudes from incisions made in the 

 bark during dry weather, and is left to harden 

 in the sun. It is of a pale yellow colour, and 



strong smell, and is somewhat semi-transpar- 

 ent. 



T<icambae. This resin is the produce of the 

 fafiara octandra, and populvs balsamifera. It 

 is brought from America in large oblong masses, 

 wrapped in flag leaves. Its colour is light brown. 

 It is brittle but easily melted by heat, and it 

 has been found to be soluble in alkalies and nitric 

 acids. 



Labdanum. This resin is obtained from the 

 cistus creticus, a shrub which grows in Candia 

 and other Grecian islands. The surface of the 

 leaves is covered with a viscid juice, which is 

 collected by a sort of rake furnished with thongs 

 of leather, to which the juice adheres. It is 

 afterwards scraped from the thongs with a knife. 

 It is very soft, and always mixed with sand and 

 dust. Its colour is blackish, its odour fragrant, 

 and its taste bitter. When dissolved in alcohol, 

 it leaves behind it a little gum. It is employed 

 in medicine as an astringent. 



Opobalsamum, or balm of Gilead. This resin, 

 which has obtained a sort of notoriety for its 

 fancied medical virtues, is the produce of 

 the amyris Gileadensis, a shrub which gi'ows in 

 Judea and Arabia; but it is so much valued by 

 the Turks, that its importation is prohibited. 

 This is the balm of Gilead so much celebrated 

 in Scripture. Pliny says it was first brought to 

 Rome by the generals of Vespasian. It is ob- 

 tained in a liquid state from incisions in the 

 bark, and is somewhat bitter to. the taste. 



Copaiva balsam. This resin is obtained from 

 the copaifera officinalis, a tree which grows in 

 South America. It exudes from artificial in- 

 cisions, having at first the consistence of oil, but 

 gradually assuming the consistence of honey. 

 It is transparent, and of a yellow colour, witli 

 an agreeable smell, but pungent nauseous taste. 

 It is a combination of resin and volatile oil, 

 which may be separated by distillation with 

 water. It is insoluble in water, but abundantly 

 ; soluble in alcohol. It is used only as a medicine. 

 Dragon's blood. This resin is obtained from 

 the draccena draco, pterocarpiis draco, and cal- 

 amiis rotang, plants that grow in the East Indies, 

 and in Spanish America. Its colour is a dai'k 

 ! red. It is tasteless and almost inodorous. Its 

 fracture is glossy, and its powder of a deep 

 crimson hue. It is brought to this country in 

 small masses, wrapped in leaves, and is used 

 I chiefly as a tooth powder. 

 I Guiac. This resin is the produce of the 

 I guiacum officinale, a tree which grows in the 

 West Indies. It exudes spontaneously, or is 

 i driven out in a melted state by means of the 

 ' action of heat. Its colour is green with some 

 \ transparency, its consistence brittle, its fracture 

 vitreous. It has scarcely any taste, and no smell ; 

 • but when thrown on burning coals it exhales a 

 ; fragrant odour. It is used in medicine. 



