COHESION OF LIQUIDS. 151 



temperatures, like oxygen, nitrogen, hydrogen, 

 and their combinations. Considering the large 

 amount of caloric which it contains, there is some- 

 thing very mysterious about the fixedness of char- 

 coal at high temperatures. 



The whole theory of distillation and sublima- 

 tion is founded on the different degrees of vola- 

 tility in the various ingredients of solid and liquid 

 bodies, from the rectification of the aethers, al- 

 cohol, and the volatile oils, to the distillation of 

 coal, by which its carbon, hydrogen, and oxygen 

 are volatilized in a state of carburetted hydrogen, 

 olefiant gas, carbonic oxide, &c. as in coal gas. 



That the proximate atoms of the fixed oils, (such 

 as olive oil, castor oil, spermaceti, lard, tallow, 

 and other bodies which are difficult to volatilize, 

 as tar, resin, beeswax,- petroleum, &c.) are larger 

 than those of the volatile oils, would appear from 

 a variety of considerations. 



1. They are generally opaque, and many of 

 them obtained by expression from the seeds of 

 plants from which it is probable that they con- 

 tain a mixture of gross particles, united with more 

 volatile particles and that they differ from es- 

 sential oils in a manner somewhat analogous to 

 the difference between smoke, which is composed 

 of gross vapours, and the pure gases, which are 

 transparent and invisible. 



2. In its ordinary state of impurity, oil of tur- 

 pentine volatilizes slowly at 300 F., when a limpid 



