52 FIRESIDE SCIENCE. 



The changes in coals and carbonaceous sub- 

 stances, which result in the production of oily 

 liquids, are effected by a process called destructive 

 distillation. If water is placed in a retort or still, 

 and heat applied, the particles are raised in the 

 form of vapor, and by condensation are resolved 

 back again into water. There is no change effected 

 in the liquid. But, if we place soft coals in an iron 

 retort, and apply heat, they are disorganized or 

 destroyed. No coal can be found in the retort, or 

 in any vessel containing the volatilized products, 

 after the operation is completed. The degree of 

 heat applied will determine whether it be resolved 

 into gaseous bodies, or into liquids and semi-solids. 

 If a cherry-red heat be kept up during the distilla- 

 tion, we have, as a chief product from the coal, 

 olefiant or illuminating gas ; if a lower, or dull red 

 heat, little gas comes over, but copious vapors, 

 which, when condensed, form a thick, black, greasy 

 fluid, of a not very inviting character. This fluid 

 is made up of a great number of substances, the 

 four most important being kerosene oil for burning, 

 oil for lubricating, paraffine, and naphtha. To 

 obtain the pure kerosene oil, the liquid is subjected 

 to several more distillations, in which strong sul- 

 phuric acid is employed to aid in the purification, 

 and the acid is afterwards removed by caustic soda. 

 Our limits are too narrow to describe the processes 



