VEGETABLE PRODUCTS. 



145 



of a clear transparent colour, almost without 

 smell or taste, and is used where fine oils are 

 requisite. • 



Rapeseed oil is extracted from the hrassica, 

 napus, and campestris. It is less fixed, and less 

 liable to become rancid than the two former, 

 and is manufactured chiefly in Flanders. 



Oil of behen is extracted from the fruit of the 

 guilandina mohringa, common in Egypt and 

 Africa. It is apt to become rancid, but is with- 

 out odour, and is on this account much used in 

 perfumery. 



Drying oils. The principal of these are lint- 

 seed oil, nut oil, poppy oil, and hempseed oil. 

 Lintseed is obtained from flax seed, which is 

 first of all roasted, in order to dry up the muci- 

 lage contained in the seed, as also to promote 

 the freer and more copious separation of the oil. 

 This oil still contains a portion of mucilage, and 

 hence perhaps its property of quickly drying 

 and hardening depends. Long boiling converts 

 it into a sort of varnish. With the oxide of 

 lead it forms a convenient lute, much used in 

 the arts. Nut oil is extracted from the hazel or 

 walnut. The kernel is first slightly roasted, and 

 then subjected to pressure, when the oil flows 

 out. It is used for food in some parts of France, 

 and in the coarser kinds of painting. It is apt 

 to become rancid. Poppy oil is procui-ed from 

 the seeds of a poppy, (papaversomniferum) which 

 is cultivated in France for this purpose. It is 

 clear and transparent, and dries readily; and 

 when pure is without taste and odour. It is 

 used for the same purposes as the olive oil, for 

 which it is often sold. Hempseed oil is procured 

 from the hemp, has a harsh and disagreeable 

 taste, and is used only for mixing up the coarser 

 paints. 



Volatile oils. A great variety of vegetables 

 contain an oil which, being of a lighter and less 

 permanent nature than the fixed oils, has been 

 called volatile or essential oil. These oils per- 

 vade almost every part of the plant. They are 

 found in many roots, to which they impart a 

 fi'Dgrant and aromatic odour, with a somewhat 

 acrid taste. The roots of imila helenium, genista 

 canariensis, and many others, contain oils of this 

 sort. They are found also in the bark, as in the 

 cinnamon tree; or in the wood, as in the sassa- 

 fras and the fir; in the leaves of labiate plants, 

 such as mint, rosemary, marjoram; and of the 

 odorous umhellifera;, such as fennel, charvil, an- 

 gelica; and of plants with compound flowers, 

 such as worm- wood. They are found also in 

 the flower itself, as in the flowers of camomile 

 and the rose; and in the fruit, as in pepper 

 and ginger; and lastly, in the external integu- 

 ments of many seeds; but never in the cotyle- 

 don. It is probable that every plant possessing 

 a peculiar odour owes this to a peculiar oil, and 

 that this aroma is caused by the volatile particles 



of the oil being continually given off from the 

 plant. Volatile oils are obtained by expression 

 from the plant, or distillation. They are char- 

 acterised by their strong and aromatic odour, 

 and rather acrid taste. They are soluble in al- 

 cohol, but are not readily converted into soaps 

 by alkalies. They are very inflammable, and 

 are volatilized 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 con- 

 sequently sink. They are much prized, on 

 account of their agreeable taste and odour, and 

 are prepared and sold under the name of distilled 

 waters or essences. Oil of turpentine is used 

 as a varnish, and for mixing with other oils in 

 the composition of pigments. 



Wax. This substance is found exuding from 

 the upper surface of the leaves of many trees. It 

 exudes also from other parts of the plants be- 

 sides the leaf, and assumes a more stiff and con- 

 crete form, as from the catkins of the poplar, 

 the alder, and the fir, from the fruit of the 

 myrica cerifera and croton scbiferum; but par- 

 ticularly from the antherse of flowers. Bees' 

 wax, though an animal production, agrees so 

 closely in all its characters with that from plants, 

 that there can be no doubt of their being the 

 same substance. It was at one time the opinion 

 of naturalists, that the bees collected their wax 

 ready formed from the pollen of plants; but 

 Huber has shown that the pollen which the bees 

 carry to their hives is employed as tlie food of 

 their larvse; and that the wax is manufactured 

 by them from the saccharine juices of the flower. 

 It exudes from the rings in the abdomen of 

 these insects, and is employed by them in con- 

 structing the walls of their cells. Wax, as it 

 comes from the bee-hive, has a yellow colour 

 and a peculiar smell, both of which are derived 

 from the honey with which the wax cells are 

 filled. To free it from these impurities, it 

 is melted in water and cast into thin ribbons, 

 which are exposed to the light of the sun, till, 

 by the joint action of the light and moisture, 

 they are bleached white. Several fusions and 

 exposures are required, however, to render it 

 perfectly pure. 



Wax, when pure, is tasteless and inodorous, 

 insoluble in water or alcohol, but combines 

 with the fixed oils, forming with them a paste 

 or cerate. It readily combines with alkalies, 

 and assumes the consistence of soap. The acids 

 have little action on it, and on this account wax 

 forms a convenient chemical lute. Wax softens 

 with heat, and melts at the temperature of 142° 

 if unbleached, and 155° when pure; at a higher 

 temperature it boils and passes ofi' into vapour, 

 which vapour may be set on fire by the appli- 

 cation of a red heat. Hence, its utility in mak- 



