COMMON COMPOUNDS OF OTHER ELEMENTS 275 



combined with the different substances sodium, potas- 

 sium, ammonium, and calcium to form the base. The 

 name alkalies is commonly applied to the first two bases 

 mentioned above. Alkalies are simply the more soluble 

 members of the class of substances called bases. Any 

 basic reaction may be called an alkaline reaction. Strong 

 alkaline solutions are " soapy " to the touch. Because 

 of their action on grease and fats, alkalies are used in 

 the manufacture of soaps, for cleaning, and for flushing 

 partially clogged waste pipes leading from sinks. 



Salts. When an acid and a base are brought together 

 in the right proportions, the characteristic properties of 

 each disappear. The hydrogen and the oxygen of the base 

 unite with the hydrogen of the acid to form water, while 

 the residues of both unite to form a salt. For example : 



Sodium hydroxide, a compound of sodium, hydrogen, and oxygen, 



reacts with 

 hydrochloric acid, a compound of hydrogen and chlorine, 



to give 

 water and common salt (sodium chloride). 



Experiment 71. Add some hydrochloric acid to a water solu- 

 tion of litmus. Now add sodium hydroxide solution drop by drop 

 until the red color disappears, leaving the solution white. The 

 acid and the hydroxide have neutralized each other. Evaporate 

 the solution to dryness and there will be a residue of white crystals, 

 the properties of which show it to be common salt. 



Uses of Salts. - - There are so many different salts that 

 a thorough discussion of their uses would involve the 

 whole subject of chemistry. However, a few common 

 salts and their uses may be mentioned with profit. 



Copper sulphate, " blue vitriol," is a blue salt having 

 a number of uses. It is used in the gravity batteries of 

 the telegraph systems. The farmer has also discovered 



