SCIENCE IN THE INDUSTRIAL WORLD 



surrounded completely except for a small vent for the 

 escape of the gases in the subsequent heating-process. 

 A very fine black pigment is made in practically the 

 same manner from the remains of the pressed grapes. 



A form of charcoal made by the dry distillation of 

 bones is known as bone black, or, in its finer qualities, 

 ivory black. To make this pigment the bones are re- 

 duced to small particles which are placed in closed 

 crucibles and heated. As a result of this heating the 

 inorganic portion of the bones is reduced to bone ash, 

 while the organic portion is reduced to pure carbon and 

 deposited on the inorganic particles. Thus the calcined 

 substance contains only about twelve per cent, of carbon ; 

 but this is sufficient for making a very good black pig- 

 ment when the mass is ground to a fine powder. If a 

 very pure article, such as that used by painters and 

 black-and-white artists, is wanted, the bone ash may 

 be removed simply by treating the ordinary bone black 

 with hydrochloric acid, which dissolves the bone ash, 

 thus liberating the particles of a very pure and very 

 finely powdered carbon. 



It is rather curious that the soot from hard wood does 

 not make good pigment, just as the charcoal from such 

 wood does not. With this restriction, however, it may 

 be said that good pigment may be made from any 

 easily combustible substance that is rich in carbon, 

 such as pine wood, resin, and the various animal and 

 mineral oils. 



From the fact that all black printing-inks, and most 

 of the best black paints and lacquers, are made from 

 soot black, it may be correctly inferred that the manu- 



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