OILS AND RESINS. 



421 



ESSENTIAL OILS. 



Oil of anise. 

 Oil of bergamot. 

 Oil of carraway. 

 Oil of cassia. 

 Oil of cedar. 

 Oil of cloves. 

 Oil of lavender. 



Oil of lemon. 

 Oil of mint. 

 Oil of myrrh. 

 Oil of nutmeg. 

 Oil of peppermint. 

 Oil of rose. 

 Oil of turpentine. 



Vegetable oils are obtained by crushing seeds ; animal oils come from 

 the whale and seal tribe. Paraffin oil comes from coal. Linseed is a very 

 drying oil, and on it depends the drying power of paint. We know olive 

 oil will not dry on exposure to the air. Oiled silk is made with linseed oil. 

 When oil is drying in the air considerable heat is evolved, and if oiled 

 substances be left near others likely to catch fire, spontaneous combustion 

 may ensue. Oil of turpentine is found in the pine 

 and fir trees, and many of the oils above mentioned 

 are used by perfumers, etc., the rose oil, or attar 

 of roses, being an Eastern compound. 



Allied to the volatile oils are the RESINS, 

 which are non-conductors of electricity. They 

 are vegetable products. They are soluble in 

 alcohol, in the volatile oils, or in ether, and these 

 solutions are called varnisJies ; the solvent eva- 

 porates and leaves the coating. Turpentine, copal, 

 mastic, shellac, caoutchouc, and gutta-percha are 

 all resinous bodies. Amber is a mineral resin, 

 which was by the ancients supposed to be the 

 " tears of birds" dropped upon the seashore. 

 Moore refers to this in his poetic "Farewell to 

 Araby's Daughter" 



" Around thee shall glisten the loveliest amber 

 That ever the sorrowing sea-bird has wept." 



Amber is not soluble either in water or alcohol ; it is, however, soluble 

 in sulphuric acid. It takes a good polish, and when rubbed is very elec- 

 trical. It is composed of water, an acid, some oil, and an inflammable gas, 

 which goes off when the amber is distilled. 



The well-known camphor is got from a tree called the "Laurus Cam- 

 phora"; it is a white, waxy substance, and can be obtained by oxidizing 

 certain volatile oils. It is generally produced from the Laurus Camphora in a 

 " still." The behaviour of a piece of camphor in pure water is curious, but 

 its motions can be at once arrested by touching the water or dropping oil on 

 the surface. This phenomenon is due to the surface tension of the liquid, 

 which diminishes when it is in contact with the vapour of the substance. 



Fig. 433. Crushing mill. 



