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. Be- 

 sides these results there frequently may be noticed another, now to be 

 mentioned. 



FIG. 5. 



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



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

 mercury, a solid substance which is insoluble in water, almost taste- 

 less, 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 gradually, 

 and we might assume that it has been converted into a gas from 

 which, upon cooling, the red oxide of mercury would be re-obtained. 

 If the apparatus for heating the oxide of mercury be so constructed 

 that the escaping gases may be collected and cooled, we shall not find 

 the red oxide in our receiver, but in its place a colorless gas, whilst at 



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