Book I. VEGETABLE CHEMISTRY. 221 



1411. Linseed oil is obtained from the seeds of flax, which are 1443. Popjra oil is extracted from the seeds of Papaver somuf- 



penerally roasted before they are subjected to any other proves, feruin, which is cultivated in France and Holland for this pur- 



fiir the purpose of drying up their mucilage and separating pose. It is clear and transparent, and dries readily ; snd when 



more oil. pure it is without taste or odour. It is used for the same pur- 



144.;. -Virf oi7 is extracted from the fruit of Curvlus -4vellana, poses as the olive oil, for which it is cften sold, and possesses 



or Juglans regia. The kernel is first slightly roasted, and the nothing of the narcotic properties of the poppy, 



oil then expressed. It is used in paintings of a coarser sort ; 1444. Hempseed oil is extracted from the seed of the hemp, 



and also in the reasoning of food, by many of the inhabitants of It has a harsh and disagreeable taste, and is used by painters in 



the middle departments of France ; but it is apt to become this country, and very extensively for food in Russia, 

 rancid. 



1445. Volatile oils. Volatile oils, which are known also by the name of essential oils, are of very common 

 occurrence in the vegetable kingdom, and are found in almost all the different organs of the plant. They 

 are found in many roots, to which they communicate a fragrant and aromatic odour, with a taste somewhat 

 acrid. The roots of Corvisartr'a Helknium, G'enista canadensis, and various other plants, contain essential 

 oils. They are found also in the bark of tlnnamomum vtrum, of Laurus Sassafras, and of Pinus ; and in 

 the leaves of labiate plants, such as mint, rosemary, marjoram ; of the odorous Umbellifera?, such as chervil, 

 fennel, angelica ; and of plants which compound flowers, such as wormwood. They are found also in the 

 flower itself, as in the flowers of chamomile, and the rose; in the fruit, as in that of pepper and ginger; 

 and in the external integuments of many seeds, but never in the cotyledon. They are extracted by means 

 of expression or distillation, and are extremely numerous; and perhaps every plant possessing a peculiar 

 odour possesses also a peculiar and volatile oil. The aroma of plants, therefore, or the substance from which 

 they derive their odour, and which is cognisable only to the sense of smell, is perhaps merely the more 

 volatile and evaporable part of their volatile oil, disengaging itself from its combinations. Volatile oils 

 are characterised by their strong and aromatic odour, and rather acrid taste. They are soluble in alcohol, 

 but are not readily converted into soaps by alkalies. They are very inflammable, and are volatilised by i 

 gentle heat. Like fixed oils, their specific gravity is generally less than that of water, on the surface of 

 which they will float; though in some cases it is found to be greater than that of water, in which they 

 consequently sink. They are much in request on account of their agreeable taste and odour, and are pre- 

 pared and sold by apothecaries and perfumers, under the name of distilled waters or essences ; as well as 

 employed also in the manufacture of varnishes and pigments. 



1146. Wax. On the upper surface of the leaves of many trees there may often be observed a sort of var- 

 nish, which, when separated by certain chemical processes, is found to possess all the properties of bees' 

 wax, and is consequently a vegetable wax. It exudes, however, from several other parts of the plant 

 besides the leaf, and assumes a more waxy and concrete form, as from the catkins of the poplar, the alder, 

 and the fir ; from the fruit of the .Vyrlca cerifera and Stilling/a sebifera ; but particularly from the anthera? 

 of the flowers, from which it is probable that the bees extract it unaltered. It was the opinion of Reaumur, 

 however, that the pollen undergoes a digestive process in the stomach of the bee before it is converted into 

 wax, though a late writer on the subject endeavours to prove that the wax is elaborated from the honey 

 extracted by the bee, and not from the pollen. It is found also in the interior of many seeds, from which 

 it is extracted, by means of pounding them and boiling them in water. The wax is melted and swims on 

 the top. Wax, when pure, is of a whitish colour, but without taste and without smell. The smell of 

 bees' wax is indeed somewhat aromatic, and its colour yellow : but this is evidently owning to some foreign 

 substance with which it is mixed ; because it loses its smell and colour by means of bleaching, and becomes 

 perfectly white. This is done merely by drawing it out into thin stripes, and exposing it for some time to 

 the atmosphere. Bleached wax is not affected by the air. Its specific gravity is 0"9600. It is insoluble in 

 water and in alcohol. It combines with the fixed oils, and forms with them a composition known by the 

 name of cerate. It combines also with the fixed alkalies, and forms with them a compound possessing 

 the properties of common soap. The acids have but little action on it, and for this reason it is useful as a 

 lute to confine them, or to prevent them from injuring cork. When heat is applied to wax it becomes 

 soft, and melts at the temperature of 142° if unbleached, and of 155° if bleached, into a colourless and trans- 

 parent fluid, which, as the temperature diminishes, concretes again and resumes its former appearance. 

 At a higher temperature it boils and evaporates, and the vapour may be set on fire by the application of red 

 heat ; hence its utility in making candles, and hence an explication of the singular phenomenon ob- 

 servable in the TJictamnus Fraxintlla. This plant is fragrant, and the odour which it diffuses around forms 

 a partial and temporary atmosphere, which is inflammable ; for if a lighted candle or other ignited body 

 is brought near to the plant, especially in the time of drought, its atmosphere immediately takes fire. 

 This phenomenon was first observed by the daughter of the celebrated Linnauis, and is explained by sup- 

 posing the partial and temporary atmosphere to contain a proportion of wax exuded from the plant, and 

 afterwards reduced to vapour by the action of the sun. The result of its combustion in oxygen gas was, 

 according to Lavoisier, carbonic acid and water, in such proportion as to lead him to conclude that 1(H) 

 parts of wax are composed of S2'28 of carbon and 1772 of hydrogen ; but, owing to the little action of 

 acids upon it, there seems reason to believe that it contains also oxygen as an ingredient. 



1447. Wax possesses all the essential properties of a fixed oil ; and fixed oils have the property of becom- 

 ing concrete, and of assuming a waxy appearance when long exposed to the air, in consequence, as it seems, 

 of the absorption of oxygen. Wax therefore may be considered as a fixed oil rendered concrete, perhaps 

 by the absorption of oxygen during the progress of vegetation. But if this theory is just, the wax may be 

 expected to occur in a considerable variety of states according to its degrees of oxygenation ; and this is 

 accordingly the case. Sometimes it has the consistency of butter, and is denominated butter of wax, as 

 butter of cocoa, butter of galam. Sometimes its consistency is greater, and then it is denominated tallow, 

 as tallow of croton ; and when it has assumed its last degree of consistency, it then takes the appellation 

 of wax. The following are its principal species : butter of cacao, butter of cocoa, butter of nutmeg, tallow 

 of croton, and wax of myrtle. 



14 18. The butter of cacao is extracted from the seeds of the 1430. Butter of nutmeg is obtained from the seeds of the 



Theobrinna Cacao or chocolate plant, either by boiling them in 1VI yristica officinalis, or nutmeg tree. 



water, or by subjecting them to the action of the press after 1451. Tallow of croton is obtained from the fruit of the 



h ivinc exposed them to the vapour of boiling water. Stilling/a sebifera. 



144L1. Bidter of cocoa is found in the fruit of Cocos nueffera or 1452. The max of myrtle is obtained from the berry of the 



cocoa-nut tree. It is expressed from the pulp of the nut, and is Jl/yrica cerifera. 

 even said to separate from it when in a fluid state, as cream 

 separates from milk. 



1433. Resins. Resins are volatile oils rendered concrete by means of the absorption of oxygen, or 

 rather perhaps by the abstraction of part of their hydrogen. They have a slight degree of transparency, 

 and their colour is generally yellowish. Their taste is somewhat acrid ; but they are without smell when 

 pure. Their specific gravity varies from 10180 to 12289. They are non-conductors of electricity, and 

 when excited by friction their electricity is negative. The species of resins are numerous. 



1154. Rosin is a species of resin, of which there are several is mixed with it while yet fluid, and incorporated by violent 



varieties. From different species of the pine, larch, and fir agitation, the residuum* is yellow rosin. The yellow n-sin is 



tree, there exudes a juice wh ch concretes in the form of tears. the most ductile, and the most generally used in the nits. 

 Its extrication is generally aided by means of incisions, and it 1455. Pitch and tar are manufactured from the resii.ous juices 



receives different appellations, according to the species from of the fir. The trunk is cut or cleft into pieces of a conve- 



which it is obtained. If it is obtained from the Pinus syl- nient size, which are piled together in heaps, and covered 



vestris, it is denominated common turpentine; from /.arix with turf. They are then set on fire, and the resinous* juice 



eurpp32*'a Ve nice turpentine : from .4mtris toxitera, fitf/sam ofCa- which is thus extricated, being prevented from escaping in a 



nadj. This juice consists of two ingredients, oil of turpentine volatile state by means of the turf, is precipitated rind collected 



and rosin. The oil is extricat.-d by distillation, and the rosin in a vessel beneath. It is partly converted into an empyreu- 



remains behind. If the distillation is continued to dryness, matic oil, and is now tar, which, by being further inspissated* 



the residuum is common rosin or colophonium ; but if water is converted into pitch. 



