Fire and Heat 125 



The products of burning sulfur, phosphorus, iron, and whatever 

 else you preserved in the bottles used in experiments with oxygen may 

 be tested for carbon dioxid. What does the test show in each case? 

 What is the name of each of the products in which oxygen occurs? 



47. Ash. A product of combustion of many kinds of fuel 

 is the ash. Ash, as the non-combustible residue, is a mixture 

 of clay and such mineral substances as phosphorus, lime, 

 potash, and iron in different compounds. Ashes of certain 

 hard woods are sometimes used as fertilizer, or are leached with 

 water for their potassium carbonate or " lye." This is useful 

 in making soap. A very small percentage of wood is incom- 

 bustible, as experience shows. Of coal about ten per cent is 

 usually estimated to be ash. Coal ash has no fertilizing value. 



48. Incomplete combustion : smoke. The flame of the 

 candle, if the wick is properly trimmed and combustion is not 

 interrupted, gives off no smoke or gases except water vapor 

 and carbon dioxid. We know from experience, however, 

 that burning may be checked in various ways, as by holding a 

 cold object, such as a porcelain or glass dish, in the flame, and 

 smoke be produced. Part of the smoke blackens the object, or 

 leaves a deposit of soot. Imperfect combustion in a range or any 

 fuel-burning appliance causes the production of quantities of 

 smoke, part of which escapes by way of the chimney and part 

 as soot clutters up the flue. The fact that smoke is produced in 

 the candle flame only when burning is checked, suggests that 

 it may be due generally to interrupted and therefore incomplete 

 combustion. If this is true, it should then be possible to make 

 combustion complete. This possibility may be tested in the 

 following simple manner 



Exercise : Smoke and soot. Put a small quantity of powdered 

 soft coal or a few small bits of dry wood in a hard glass test tube, and 

 close the tube with a rubber stopper in which is inserted a piece of 

 small diameter glass tubing with one end drawn to a fine tip. Heat 

 to a high temperature. When smoke issues freely from the tip, 

 apply to it a lighted match. Does the smoke ignite and burn ? Heat 

 until no more smoke appears. Remove the charred substance from 



