122 



CHEMISTRY. 



Chrmira) the whole genii* derived their name : for rosin it fre- 

 cmJ- denominated rc>in. 

 j j etm| mt y jjg dutinguifbcd by the following pro- 



They ire solid subitaucet, naturally brittle ; have a 

 proptrtic*. certain degree of trantparency, and a colour most com- 

 monly inclining to yellow. Their taite it more or less 

 acrid, and not like that of volatile oils ; but they have no 

 smell unless they happen to contain some foreign body. 

 Ttu-y are all heavier than water. Tluy arc all non-con. 

 ductors of electricity ; and when excited by friction, their 

 electricity is negative. 



Their specific gravity varies considerably. 



When exposed to heat, they melt 5 and if the heat be 

 increased, they take fire, and burn with a strong yellow 

 flame, emitting at ihe same time a vast quantity of smoke. 



They are all insoluble in water whether cold or hot ; 

 but when they arc melted along with water, or mixed 

 with volatile oil, and then distilled with water, they srcm 

 to unite with a portion >( that liquid ; for they become 

 opake, and lose much of their briuleness. This at least 

 is the case with common rosin. 



They are all, with a few exceptions, soluble in alcohol, 

 especially when assisted by heat. The solution is usual- 

 ly transparent ; and when the alcohol is evaporated, the 

 resin is obtained unaltered in its properties. 



Several of them are soluble in fixed oils, especially in 

 the drying oils. The greater number are soluble in the 

 volatile oili ; at least in oil of turpentine, the one com- 

 monly employed. 



Mr Hatchett first examined the action of fixed alkalies 

 on resins, and ascertained, contrary to the received opi- 

 nion of chemists, that alkaline leys dissolve them with 

 facility. He reduced a quantity of common rosin to 

 powder, and gradually added it to a boiling lixivium of 

 carbonate of potash ; a perfect solution was obtained of 

 a clear yellow colour, which continued afu-r long exposure 

 to the air. The experiment succeeded equally with car- 

 bonate of soda, and with solutions of pure potash, or so- 

 da. Every other resin was dissolved as well as rotin. 



These alkaline solutions of resins have the properties 

 of soap, and may be employed as detergents. When 

 mixed with an acid, the resin is separated in flakes, usual- 

 ly of a yellow colour, and not much altered in its nature. 



Ammonia acts but imperfectly upon resins, and does 

 not form a complete solution of any of those bodies 

 hitherto tried. 



It was the received opinion of chemists, that acids do 

 not act upon resins. Mr Hatchctt first ascertained this 

 opinion alto to be erroneous, and showed that most of 

 the acids dissolve resmt with facility, producing different 

 phenomena according to circumstances. 



When sulphuric acid is poured upon any of the resins 

 in powder, it dissolves them in a few minutes. At first 

 the solution is transparent, of a yellowish brown colour, 

 and of the consistency of a viscid oil, and the resin may 

 be precipitated nearly unaltered by the addition of water. 

 If the solution be placed on a sand bath, its colour be- 

 comes deeper, sulphurous acid gas i emitted, and it be- 

 comes very thick, and of an intense black. 



Nitric acid likewise dissolve! the resins with facility, 

 but not without changing their nature. Mr Hatchctt 

 was first led to examine the action <.( this acid on resins, 

 by observing that resins are thrown down by acids from 

 their toluttont in alkalies in the state of a curdy precipi- 

 tate ; but win n nitric acid is added in (Xcess, the whole 

 of the precipitate is re-dissolved in a boiling heat. He 

 poured nitric <icid of the specific gravity 1.38, on pow- 

 dered rosin in a tubulated retort ; and by repeated distil- 



lation formed a complete solution of a brownish yellow 

 colour. The tolution takes place much sooner in an Examiiuu 

 open matrass than in close vessels. The solution con- ""' 

 tinucs permanent, though left exposed to the air. It be- ^ ^ 

 comes turbid when water is added ; but when the mixture * "" Y ^ 

 is boiled, the whole is re-dissolved. 



When the digestion of nitric acid upon a resinous sub- 

 stance is continued long enough, and the quantity at acid 

 is sufficient, the dissolved resin is completely changed ; 

 it is not precipitated by water; and by evaporation, a 

 viscid substance of a deep yellow colour is obtained, 

 cquilly soluble in water and alcohol, and seemingly in- 

 termediate between resin and extractive. If the abstrac- 

 tion of nitric acid be repeated, this substance gradually 

 assumes the properties of artificial tannin. Thus it ap- 

 pears that nitric acid gradually alters the n ture ot re- 

 sin, producing a suite of changes which terminate in ar- 

 tificial tannin, upon which nitric acid has no action. 



Muriatic acid and acetic acid dissolve resin slowly, 

 anci it may be precipitated again from them unaltered. 



When resins arc subjected to destructive distillation, 

 we obtain carbureted hydrogen and carbonic acid gas, 

 a very small portion of acidulous water, and much em- 

 pyreumatic oil. The charcoal is light and brilliant, 

 and contains no alkali. 



II. Having now described the general properties of Rwinof 

 resinous bodies, it will be proper to take a more parti most im- 

 cular view of those of them which are of the most im pprtance, 

 portance, that we may ascertain how far each possesses vlz ' 

 the general characters of resins, and by what peculiarities 

 it is distinguished from the rest. The most distinguish- 

 ed of thi- resins art the following. 



1. Rusin This Hib-.tai.ee is obtained from different ji in 

 species -.ti fir ; as the jiinus abies, sylvesfris, larii, lialsa- 

 mea. It is well kn >wn that a resinous jiiice exudes 

 from the pinus tylvcsiris, or common Scotch fir, which 

 hardens into tears. The same exudation appears in the 

 piiiii* abies, or spruce fir. Tlu-se tears constitute the 

 substance called thus, or common frankincense. When 



a portion of bark is stripped off these trees, a liquid 

 juice flows out, which gradually hardens. This juice has 

 obtained different nan. is according to the plant from 

 which it comes. Tii" pinu.< s>,/:-ts(ri.t uelds common 

 t/i/i>fiitine ; the liiris, I'ctiice turpentine ; the tiaiumca, 

 balsam of Canada, &c. All th si juices, which are com- 

 monly distinguished by the name ot turpentine, an.- con- 

 sidered as composed of two ingredients; namely, oil of 

 turpentine and rosin. 



According to the experiments of Thciiard and Gay Compoii-, 

 Lussac, it is composed of 



Carbon .... 75-944 



Oxygen . . . 1.1. .37 



Hydrogen . . 10.719 



10U.OOO 



2. Mastich. This resin is obtained from the pistacia Mastica, 

 leniiscus ; a tree which grows in the Levant, particular- 

 ly in the island of Chios. When transverse incisions are 



made into this tree, a fluid exudes, which soan concretes 

 into yellowish semitransparent brittle grains. It softens 

 when kept in the mouth, but impann very little taste. 

 When heated, it melts and exhales a fragrant odour. 

 Its taste is slight, but not unpleasant. In Turkey, 

 great quantities of it are said sitiil to be chewid for sweet- 

 ening the breath, and strengthening the gums. It is to 

 this use of the resin as a masticatory that it i.-. supposed 

 to owe its name. Mastich docs not dissolve completely 

 in alcohol ; a soft elastic substance separates during the 

 solution. The nature of this insoluble portion was first 



