II. 



PRINCIPLES OF CHEMISTRY. 



RESULTS OF THE ATTRACTION BETWEEN ATOMS. 



5. CHEMICAL DIVISIBILITY. 



Decomposition by heat. The results of the action of heat upon 

 matter have been stated to be : Increased velocity of the motion 

 of molecules, increase in volume of the substance heated, and in 

 many cases a conversion of solids into liquids and of these into 

 gases. Besides these results, another effect may be frequently 

 noticed which has not yet been mentioned. 



To illustrate this action of heat, we will select the red oxide 

 of mercury, a solid substance which is insoluble in water, almost 

 tasteless, and of a brick-red color. When this oxide of mercury 

 is placed in a glass tube and heated, it will be found to disappear 



FIG. 5. 



Decomposition of mercuric oxide in A; collection of mercury in B, and of oxygen in C. 



gradually, and we might assume that it has been converted into 

 a gas from which, upon cooling it, the red oxide of mercury 

 would be re-obtaiued. If the apparatus for heating the oxide of 

 mercury is so constructed that the escaping gases may be col- 



