CHEMICAL PHILOSOPHY (CONTINUED). 45 



affinity for oxygen that phosphorus has, the abundance of 

 this substance in the earth would occasion wide-spread con- 

 flagrations. Examples illustrating the same truth could be 

 cited to any extent, but these will suffice. 



40. Modifiers of Chemical Attraction. The force of chem- 

 ical attraction varies not only with respect to the different 

 substances between which it is exerted, but it is greatly 

 influenced by certain circumstances independent of the sub- 

 stances themselves. Solution has so much influence upon 

 affinity, or the disposition of substances to act chemically 

 upon each other, that it has given rise to a maxim set 

 down by the older chemists, " Coipora non agunt nisi sint 

 soluta" substances do not act unless dissolved. A famil- 

 iar illustration of this we have in the mixture of common 

 soda powders. If the powders of tartaric acid and sodium 

 carbonate be mingled dry, there will be no action ; but if 

 each be dissolved before they are mixed, the action will be 

 immediate, producing a brisk effervescence. There are two 

 reasons for this : First, the particles are brought nearer to- 

 gether in solution than they can be mixed in powder, how- 

 ever finely they may be pulverized ; and, secondly, they 

 are free to move about among each other. Water, aside 

 from the chemical actions which itself produces, exerts a 

 very great agency as a solvent in the chemical changes 

 ever going on in all parts of the earth ; and not only so, 

 but it acts as a distributor, often bringing substances to- 

 gether which otherwise could never have come within the 

 range of each other's chemical action. 



41. Influence of Heat. Alteration of temperature is an- 

 other of the causes which modify the attractive force ex- 

 erted between atoms. Both composition and decomposi- 

 tion are effected by the influence of heat. How this can 

 be we will explain. Heat expands all bodies, or, in other 

 words, spreads the molecules farther apart; but, as you 



