THE MORE COMMON ELEMENTS AND COMPOUNDS 23 



(HC1); but these acids also react with bases (metals, metallic 

 oxids, or metallic hydroxids), as shown above for the oxygen acids, 

 thus: 



Fe + 2 HC1 = FeCl 2 + H 2 . 



CaO + 2 HC1 = CaCl 2 + H 2 O. 



NaOH + HC1 = NaCl 2 + H 2 O. 



In these reactions the salts formed are chlorids. The last equa- 

 tion shows the reaction between sodium hydroxid, which is ordi- 

 nary concentrated lye, a poisonous substance, and hydrochloric 

 acid, which is also a poisonous substance; and the salt formed is 

 sodium chlorid (NaCl), the common table salt, and the most 

 abundant salt of the ocean. 



Hydrosulfuric acid (H 2 S) also forms many salts, called sulfids, 

 as iron sulfid (FeS), calcium sulfid (CaS), etc. 



In all of these reactions the number of pounds of any base re- 

 quired to react with a given amount of any acid is easily and accu- 

 rately computed, and the amount of the salt to be formed and of 

 the water or hydrogen to be liberated can also be told in advance, 

 if one knows the atomic weights and the equation for the reaction. 

 Thus, 40 pounds of sodium hydroxid will react with 36.5 pounds 

 of hydrochloric acid, and form 58.5 pounds of common salt and 

 1 8 pounds of water. It will be seen that 76.5 pounds of materials 

 are used, and that 76.5 pounds of products are formed. In like 

 manner, all such equations must balance. In other words, the num- 

 ber and kind of atoms and the total quantity of materials put into 

 the reaction on one side of the equation must be exactly the same 

 as appear in the products on the other side of the equation. 



Acid salts are salts which still contain some of the hydrogen of 

 the acid from which they were made. Thus, if we supply only one 

 half as much potassium as would be required to react with a cer- 

 tain amount of sulfuric acid, if an acid salt is possible, it will be 

 formed : 



KOH + H 2 SO 4 = KHSO 4 + H 2 O. 



The sulfuric acid molecule has two hydrogen atoms, and, to 

 make neutral potassium sulfate, both hydrogen atoms must be 

 replaced with potassium atoms; but in the equation here shown, 

 only one potassium atom is provided. Consequently, only one 



