DRY DISTILLATION. 711 



the benzin of Mitscherlich and bicarburet of hydrogen of 

 Faraday. The neutral benzoate of lime gives with other pro- 

 ducts the liquid benzone, C 13 H 5 O. Distilled from lime stearic, 

 margaric and oleic acids lose the elements of carbonic acid, and 

 form neutral volatile products, stearone, margarone and oleone. 

 The names of such pyrogen bodies terminate in one as contain 

 one atom of oxygen and are neutral. Margarone carried in its 

 turn over lime at a red heat, loses its oxygen, in the form of 

 carbonic acid, and paraffin is produced, which is a binary com- 

 pound of carbon and hydrogen. Thus the alkali determines 

 throughout the formation of a highly oxidised acid body, with 

 which it unites and the other products are consequently partially 

 or completely deoxidised. 



Dry distillation. Many organic substances are volatile and 

 may be distilled at a moderate heat without alteration, such as 

 alcohol and most essential oils ; but a larger number are fixed. 

 The latter when submitted alone to distillation usually abandon 

 carbon, and form new and more simple volatile products. 

 Three periods are distinguished by Liebig in the dry distillation 

 of the fixed organic acids, from the different compounds formed 

 according to the temperature. In the first, organic acids of 

 less atomic weight are produced, with carbonic acid, water and 

 inflammable liquids soluble in water. The bibasic and tribasic 

 organic acids, by losing the elements of water and carbonic acid, 

 are converted into their volatile pyr-acids, which are less basic, 

 generally monobasic ; thus tartaric acid C 8 H 4 O 10 is converted 

 into pyrotartaric acid C 5 H 3 O 3 , by losing three atoms of car- 

 bonic acid C 3 O 6 and one atom of water HO ; but these pyr-acids 

 can rarely be distilled again by themselves, without partial de- 

 composition. In the second period of the distillation, bodies 

 are obtained which result from the destruction of the preceding 

 compounds ; thus the oxygen of the acids, uniting with the 

 carbon and hydrogen of the combustible bodies, gives rise to 

 more simple bodies, such as carbonic oxide, carbonic acid and 

 water ; some charcoal is generally set at liberty, while another 

 portion of it enters into combination with the excess of hydro- 

 gen, and produces liquid or solid volatile hydrocarbons. In 

 the last period, nothing is obtained but charcoal and a gaseous 

 mixture, principally composed of carbonic acid, carbonic oxide, 

 olefiant gas and light carburetted hydrogen. Substances con- 



