COAL, SOFT AND HARD 193 



short time, lignite was formed. After a longer time bitu- 

 minous coal resulted, while anthracite coal is the result of 

 complete change. 



In peat bogs we have a form of very impure carbon, yet 

 peat may be dried and burned. There are factories, also, 

 where peat is ground up, mixed with petroleum, and then 

 compressed into blocks. This produces an economical fuel. 



Anthracite coal is almost pure carbon, and, if heated, gives 

 off but very little gas. Therefore this coal burns almost 

 without flame. See Section 10, Flames. Since the process 

 of natural destructive distillation has not gone as far in 

 the case of bituminous as of anthracite coal, the former sets 

 free a large amount of gas when heated, and burns with a 

 smoky flame. Bituminous coal is used to manufacture coal 

 gas. See Section 28, Destructive Distillation. 



Coal is not affected by acids, but is attacked quite vigor- 

 ously by the oxygen of the air. This is especially true of 

 bituminous coal, and spontaneous combustion often takes 

 place in piles of coal where the ventilation is poor. 



References : 



1. 1205:352-354. How Coal was Made. 



2. 1407:341-342. Coal. 



3. 1702:48. Coal. 



4. 1710:28-29. Coal, 

 a. 1203:226-230. Coal. 



6. 1204 : 38-45. The Coal-making Time in North America, 



c. 1206 : 460-463. How Coal was Made. 



d. 1210 : 301-311. Origin of Coal and its Varieties. 



e. 1701:199. Coal. 

 /. 1704:168-169. Coal, 

 flf. 1705:186-187. Coal. 

 h. 1706:184-187. Coal. 

 i. 1707:183-184. Coal. 



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