SOME CHEMISTRY OF EVERYDAY LIFE 181 



taste, even as there are bases without the characteristic 

 effects of ammonia and lime water on litmus paper. The 

 chemist resorts to other means of classification than taste, 

 or effect on litmus, to establish the distinctions between 

 these important classes of chemical compounds. 



To aid in making somewhat clear the distinctions that 

 are fundamental in this classification, let us make use of the 

 formula employed by chemists to express what is known of 

 the chemical composition of some of the substances listed 

 as acids, bases, and salts. Only a few of these can be given 

 here. Through the use of formulae the chemist employs 

 a short-hand expression of his knowledge of the composition 

 of substances, naming the chemical elements that enter into 

 their composition. He likewise reads into a chemical formula 

 the weight proportions of the elements, and many other 

 facts that are not apparent to one who has not studied Chem- 

 istry. It is possible to tell from the formula whether a 

 substance is an acid, a base, or a salt. 



In the formulae of the chemical compounds given below, 

 note what is common in those (a) of the acids; (6) of the 

 bases; (c) of the salts 1 . 



Acids Bases Salts 



hydrochloric, HC1 sodium hydroxide, NaOH sodium chloride, NaCl 



nitric, HNO 3 potassium hydroxide, KOH potassium nitrate, KNO 3 



sulphuric, H 2 SO4 calcium hydroxide, Ca(OH) 2 calcium sulphate, CaSO4 



hydrosulphuric, H^S copper hydroxide, Cu(OH) 2 copper sulphide, CuS 



The chemist makes large use of the theory that when any 

 one of these substances is put into water some of its mole- 

 cules break up. This dissociation fo molecules always 

 yields two parts, and each consists of an atom or a group of atoms 

 that is electrified. One of these electrified parts of a mole- 

 cule (an ion) has electricity of one kind (positive), and the 



1 It is to be remembered that all these are used as illustrations only, and 

 that any complete discussion of this topic belongs in Chemistry. 



