304 REPORT OB' NATIONAL MUSEUM, 1899. 



The chief commercial use of the material is based upon its highl}^ 

 refractor}^ or noncombustible nature. The popular impression that it 

 is a nonconductor of heat is, according to Professor Donald, erroneous, 

 the nonconducting character of the prepared material being due rather 

 to its porous nature than to the physical properties of the mineral 

 itself.^ Owing to the comparative high price of asbestos, it is, in the 

 manufacture of the so-called nonconducting materials, largely admixed 

 with plaster of paris, powdered limestone, dolomite, magnesite. diato- 

 maceous earth, or carbonaceous matter, as hair, paper, sawdust, etc. 

 With the possible exception of the magnesite (carbonate of magnesia) 

 these are all less effective than the asbestos, and deteriorate as well as 

 cheapen the manufactured article. The following table will serve to 

 convey some idea of the relative portions of the various materials used 

 as nonconducting pipe coverings, etc. : 



Asbestos sponge, molded: 



Plaster of paris on 



Fibrous asbestos "*• "0 



100. 00 



Fire felt sectional covering: 



Asbestos , 82. 00 



Carbonaceous matter ( hair, paper, sawdust, etc. ) 18. 00 



100. 00 



Magnesia sectional covering: 



Carbonate of magnesia 92.-0 



Fibrous asbestos 7. 80 



100. 00 



Magnesia plastic: 



Carbonate of magnesia 91.. 20 



Fibrous asbestos 7- ^^ 



100. 00 



Asbestos cement felting: 



Powdered limestone 64. 50 



Plaster of paris ^-^^ 



Asbestos ^^-QQ 



100. 00 



Asbestos sponge cement felting: 



Powdered limestone 59. 00 



Plaster of paris 10. 00 



Asbestos '^l- 00 



100. 00 



Fossil meal: 



Insoluble silicate 75. 00 



Carbonaceous matter ( hair, paper, sawdust, etc. ) 11. 00 



Soluble mineral matter 8. 00 



Moisture 6. 00 



100. 00 



iThe Mineral Industry, II, 1893, p. 4. 



