78 CHEMISTRY. 



gases only, and all that would be visible is the ashes. But, as 

 it is, there pass upward in this body of vapor and gas solid 

 particles of carbon that failed to be burned, and it is these that 

 you see and call smoke. These accumulate to some extent in 

 a chimney upon its sides. The soot thus formed is not pure 

 carbon, for there are some other substances creosote, etc. 

 mingled with it. The reason that we do not have smoke and 

 soot from hard coal is that the combustion is more perfect 

 than in the case of wood. So, too, there is more of smoke, 

 and therefore soot, from green wood than there is from dry 

 wood. For this reason green or wet wood is used in smok- 

 ing meat. When a lamp smokes from having the wick too 

 high, it is because the carbon of the oil is furnished in too 

 large quantity for the oxygen that is in the air around the 

 wick. Whatever this smoke touches has soot deposited 

 upon it. When the combustion is perfect, all the carbon, 

 as it rises in the heated wick, is made by the heat to unite 

 with the oxygen of the air, and form carbonic anhydride, 

 which passes upward unseen. 



92. Lampblack. This substance, so much used in making 

 printing-ink, is a fine kind of soot 

 made from pitch or tar. In Fig. 20 

 is represented an apparatus for mak- 

 ing lampblack. In the iron pot, a, 

 some pitch or tar is heated to boil- 

 ing, and, as a little air is admitted 

 through small openings in the brick- 

 work around the pot, an imperfect 

 combustion takes place. The carbon 

 of the tar passes in a dense cloud of 

 smoke into the chamber, b c. In this 



hangs a cone of coarse cloth, the height of which may be 

 regulated, as you see, by a pulley. The lampblack or car- 

 bon is deposited in powder on the cone and on the sides of 



