152 



SCIENCE OF GARDENING. 



Paht II. 



677. 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 aU the different organs of the plant. They 

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

 acrid. The roots of inula helenium, genista canariensis, and a variety of other plants, contain essential 

 oils. They are found also in the bark of laurus cinnamomum, of laurus sassafras, and pinus ; in the leaves 

 of labiate plants, such as mint, rosemary, marjoram ; and of the odorous umbelliferae, such as chervil, 

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

 flower itself, as in the flowers of chamomile, and the rose ; and 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 

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

 they derive their odor, and which is cognisable only by 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 odor, 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 a 

 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 odor, 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. 



678. 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 myrica cerifera and croton sebiferum ; 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 color, but without taste and without smelL The smell of 

 bees' wax is indeed somewhat aromatic, and its color yellow. But this is evidently owing to some foreign 

 substance with which it is mixed, because it loses its smell and color 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 09600. 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 colorless 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 vapor 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 dictamnus fraxinella. This plant is fragrant, and the odor 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 Linnaeus, 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 vapor by the action of the sun. The result of its combustion in oxygene gas was, 

 according to Lavoisier, carbonic acid and water, in such proportion as to lead him to conclude that 100 

 parts of wax are composed of 82-28 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. 



679. Wax possesses all the essential properties of a fixed oil. But 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 degree of oxygenation ; and this is ac- 

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

 butter of coco, 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 coco, butter of nutmeg, tallow of 

 croton, and wax of myrtle. 



. * 680 ; ?!" ^ ler "fS a f ao is extracted from the seeds of the theobroma cacao or chocolate plant 

 Ifa; 55.), either by boiling them in water, or by subjecting them to the action of the press after 

 having exposed them to the vapor of boiling water. 



Butter of coco is found in the fruit of the cocos nucifera or coco-nut-tree. It is expressed 

 from the pulp of the nut, and is even said to separate from it when in a fluid state, as cream sepa- 

 rates from milk. r 



Butter of nutmeg is obtained from the seeds of the myristica officinalis, or nutmeg-tree. 



Tallow of croton is obtained from the fruit of the croton sebiferum. 



The wax of myrtle is obtained from the berry of the myrica cerifera. 



681. 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 color is 

 generally yellowish. Their taste is somewhat acrid ; but they are without 

 smell when pure. Their specific gravity varies from 1-0180 to 12289. They 

 are non-conductors of electricity, and when excited by friction their electri- 

 city is negative. The species of resins are numerous. 



&it. Rosin is a species of resin, of which there are several varie- 

 ties From different species of the pine, larch, and fir-tree, 

 there exudes a juice which concretes in the form of tears. Its 

 extrication is generally aided by means of incisions, and it re- 

 ceives different appellations, according to the species from 

 which it is obtained. If it is obtained from the pinus syl- 

 vestris, it is denominated common turpentine ; from pinus larix, 

 Veince turpentine ; from amyris balsamea, balsam of Canada. It 

 consists of two ingredients, oil of turpentine and rosin. The 

 >* extricated by distillation, and the rosin remains behind. 

 It the distillation is continued to dryness, the residuum is 

 common rosin or colophonium ; but if water is mixed with it 

 while yet Hind, and incorporated by violent agitation, the resi- 

 tluum is yellow romn. The yellow rosin is the most ductile, 

 and the most generally used in the arts. 



t>H3. Pitch and tar are manufactured from the resinous juices 

 t the fir. 1 he trunk is cut or cleft into pieces of a convenient 



size, which are piled to- 

 gether in heaps, and co- 

 vered with turf. They are 

 then set on fire, and the 

 resinous juice which is thus 

 extricated, being prevented 



,^j??l" g j n u volatile state ^ means of tJ * *irf, i* 

 precipitated and collected in a vessel beneath. It is partly con 

 verted mto an empyreumatic oil, and is now tar, which, bv 

 being further inspissated, is converted into pitch. ' 



Mastich is extracted from the pistacia lentiscus. 

 Une^urexudation 131 " 611 fr m the ^^^ *. by spon- 



Elemi is extracted from the amyris elemifera- 

 ba^amSeTa'. ^ Mroduce of the & *andra and V opulus 



Labdanum is obtained from the cistus creticus. . 



