8 



CHEMISTRY OF FARM PRACTICE 



may be further oxidized by adding to itself another atom 

 of chlorine, forming mercuric chloride or corrosive sub- 

 limate. 



9. Combustion. Oxidation produces heat as a result 

 of the chemical action taking place. Should oxidation be 

 sufficiently rapid to produce enough heat so that light is 

 evolved, the process is termed combustion. When the 

 materials entering into combustion are gases, a flame is 

 produced. Burning wood is undergoing combustion, this 

 process of oxidation being supported by the oxygen drawn 

 from the atmosphere entering into rapid union with the 

 hydro-carbon gases produced from the heated wood. The 

 three conditions necessary for combus- 

 tion are first, a combustible substance; 

 second, a supporter of combustion; 

 third, a kindling temperature. Usually 

 carbon or hydrogen or some of their 

 numerous compounds or the metals that 

 are easily oxidized are regarded as the 

 combustibles, while oxygen or some of 

 the elements that act chemically like 

 oxygen are considered the supporters of 

 combustion. The material entering into 

 chemical reaction which is the more 

 abundant is likely to be considered the 

 supporter of combustion, and thus the 

 Gas combustible and the supporter of com- 

 bustion may exchange places. 



This is seen in the reversal of flames 

 FIG. 2. Apparatus effected by the apparatus in Fig. 2. The 



lamp chimney is fitted with corks and tubes 

 versal of names. . t < 



as in the figure. The straight glass tubes 



at A and C are at least -^ of an inch in internal diameter. 

 The glass elbow D is connected with the illuminating gas 

 supply. While the finger is placed at C, closing the tube, 

 the gas is turned on and allowed to flow till the chimney 



