142 RESINS. 



exudes from certain laurels ; it is from the Laurus camphora that 

 all the camphor of commerce is extracted in the East, the extraction 

 being effected precisely by the same process as other essential oils. 

 The chips of tiie Laurus cam-phora are put into iron stills, surmount- 

 ed by earthenware capitals, in the inside of which a number of 

 ropes made of rice-straw are stretched ; the camphor rises and ia 

 condensed on the surface of these cords in the state of a gray pow 

 der ; it is refined by sublimation. 

 According to M. Dumas, camphor contains : 



Carbon ... 79.2 



Hydrogen 10.4 



Oxygen 10.4 



100.0 



OF RESIN. 



Essential oils almost always hold certain substances in solution 

 which make them viscid or sticky. The balsams which exude from 

 the bark of certain trees are nothing more than solutions of resin in 

 essential oils. When the volatile oil has been dissipated by evapo- 

 ration, the resin remains in the solid state. There is further a nat- 

 ural relation in point of constitution between essential oils and resins. 

 The greater number of essences absorb, as we have said, oxygen 

 from the atmosphere, and by this absorption they become thick, and 

 are changed into resins ; so that in one case the resin may be a 

 product of the oxidation of an essential oil, in another it may merely 

 be set at liberty by the dissipation of the essence which held it in 

 solution. 



The resins constitute friable, or soft solids. They are fusible, 

 extremely inflammable, and fixed. The resins are inodorous when 

 pure : any odor which particular resins possess is generally attrib- 

 uted to the essential oil which they still retain. The resins are in- 

 soluble, or very sparingly soluble in water ; some of them dissolve 

 readily in alcohol and in ether, and there are some also, such as 

 copal, which are only soluble in very small quantity. Some resins 

 show acid reaction ; they combine with bases, neutralizing them. 

 The greater number of resinous matters obtained from plants are 

 regarded by chemists as mixtures of several particular resins, the 

 study of which is not ye*, much advanced. Some resins are much 

 employed in the arts, such as colophony and copal, &c. Several 

 balsams are also in familiar use, particularly as medicines, such as 

 the balsam of tolu, balsam of copaiba, &c. 



Colophony, or rosin, is extracted from different kinds of the genus 

 Pinus. In the Landes, or sandy plains of Bordeaux, it is the mari- 

 time pine which yields it. When the tree is from thirty to forty 

 years of age, incisions are made in the trunk, beginning at the lower 

 part, two or three times a week, ,and these are continued to the 

 height of from 6 to 10 feet from the ground ; the last notch general.. 

 ly reaches this height about four years after the tree has been notch- 

 ed for the first time. After this a new series of notches is be^un 

 pa the opposite side, setting out from the ground as before, and in 



