1 82 GENERAL SCIENCE 



other part has the opposite kind of charge (negative). When 

 these ions reunite, this electrification disappears, the one 

 kind neutralizing the other. A substance which thus breaks 

 up into ions is called an electrolyte. 



He explains that the acid' effect of liquids on litmus paper 

 is due to the existence of free hydrogen (H) ions, and the 

 basic effect is due to free hydroxyl (OH) ions. The neutrali- 

 zation of an acid by a base then becomes simply a chemical 

 union of these ions to form H 2 O (water), and the withdrawal 

 from solution of both acid and basic ions. 



Such conceptions as these make possible an understanding 

 of chemical changes otherwise unsatisfactorily explained. 



It must be noted, too, that the salt whose formula is given 

 in every one of the cases exhibits in its formula a relation- 

 ship to both the acid and the base. A salt in chemistry is 

 defined as a compound considered as having been formed in 

 the reaction between an acid and a base. These changes 

 as they are supposed to occur may be expressed in the form 

 of equations. The formulae before the sign of equality rep- 

 resent the substances that as factors enter into the chemical 

 change; those after it represent the substances that are 

 products of the change. While these equations are often 

 employed to express what we think may happen, it is to be 

 remembered that their use by the chemist is supposed to 

 express what is known to have happened. 



It will be noted in the formulas of all salts that the hydro- 

 gen of the acid has been replaced by atoms of the metallic 

 element of the base. This illustrates one of the best of defini- 

 tions of acids, i.e., a substance whose molecules contain 

 hydrogen atoms that are replaceable by a metal. A base 

 appears to be a substance whose molecules consist of metallic 

 atoms combined with the hydroxyl group (hydroxyl radical). 

 These definitions will come to have a much greater sig- 

 nificance with a better knowledge of Chemistry. The term 



