CHAPTER VI 



WATER 



WATER is not an element like oxygen, nor is it a mixture 

 such as we have found air to be, but a compound of two 

 elements, hydrogen and oxygen. Water as it occurs 

 in nature usually has a number of other substances, such 

 as limestone, different salts, and carbon dioxide, dissolved 

 in it ; but pure water is composed of only 

 the two substances named above. 



It is quite easy to separate water into 

 the elements which compose it by elec- 

 trolysis, which means " breaking apart " 

 or analysis by the aid of electricity. 



Electrolysis of Water. - - The commer- 

 cial piece of apparatus sold for this ex- 

 periment is called a Hoffmann apparatus 

 (Figure 90). However, if such an appa- 

 ratus is not available, the experiment 

 may be performed very well by such an 

 apparatus as shown in Figure 91. The 

 water used should be slightly acidulated 

 with sulphuric acid, and the wires leading from the bat- 

 tery should terminate in platinum foil. The ends of the 

 wires are called poles or electrodes. The test tubes are 

 filled with water and suspended over the electrodes so 

 that the mouths of the test tubes shall be below the level 

 of the water in the pan. The amount of electricity needed 



FIG. 90. Hoffmann 

 Apparatus. 



