MIXTURES 215 



the fibrous mass spread evenly. An endless strip of 

 cloth now picks up this fibrous mass, carrying it through 

 several rollers. After passing through these, the paper 

 is strong enough to go on through several more rollers 

 without the cloth. The rollers are heated, and they 

 press the fiber so firmly together that the mass becomes 

 paper. Wood pulp is often mixed with the fibers from 

 rags ; some cheaper papers are made largely of wood 

 pulp. Since it is made from wood and cloth fibers, 

 paper also must be mostly cellulose. 



Experiment 136 . Into one crucible put a mass of cotton 

 threads, and into another some bits of paper. Cover each sub- 

 stance with a little dry sand, heat for a few minutes, and examine. 



253. Coal. Millions of years before man appeared 

 on earth plants grew upon its surface. In some places 

 large masses of trees, leaves, ferns, and other plant 

 forms were piled up as they died, and were later cov- 

 ered by layers of soil and rock. 

 These slowly decomposed, much 

 of the gaseous part of the wood 

 passing off, but the carbon remain- 

 ing. In time these masses became 

 hard, and to-day we find them in 

 the earth as coal. Thus we see FIG. 141 



that coal contains the same elements that are found in 

 wood, but the gaseous elements are much less in quantity 

 and the C largely remains. 



Anthracite contains more carbon and less of other 

 elements than soft coal. Some anthracite is over nine 

 tenths carbon ; it is the hard kind, such as is burned in 



