PHYSICIST'S AND CHEMIST'S VIEW 



9 



hydrogen to one part of oxygen, is expressed by the formula H2O 

 by the chemist and is called a chemical compound. 



Both oxygen and hydrogen are colorless, tasteless, and odorless, 

 but hydrogen differs from oxygen by igniting with a slight explosion 

 when it is mixed with a little air and a burning match or splinter 

 is introduced in it. As it burns, drops of water are formed, show- 

 ing that the hydrogen is uniting again with oxygen to form water. 

 Hydrogen has a great chemical affinity for other elements ; hence 

 it is usually found in nature 

 combined with other ele- 

 ments, as, for example, with 

 oxygen in water. 



The Place of Water in the 

 Environment. — Water, in 

 the form of rain, snow, or 

 ice, or in river, lake, or sea, 

 forms a very important part 

 of our environment. It car- 

 ries soil or mineral sub- 

 stances, sometimes as sedi- 

 ment, sometimes in solution. 

 The water of the ocean holds 

 salts in solution. If sea water is boiled until it is all evaporated, 

 the salts will remain. If water is poured over them, they will 

 dissolve or become solutes (s6-lutsO . In other words, the salts 

 become divided into very minute particles which distribute them- 

 selves through the liquid. But there are great differences in the 

 solubility of substances. Some, like common salt or sugar, are 

 very soluble ; others, such as lime and iron, very insoluble. Pure 

 water containing no solutes is rarely found in nature. 



Oxidation. — Oxygen has the very important property of unit- 

 ing with many other substances. The chemical union of oxygen 

 with another substance is called oxida'tion. Rapid oxidation pro- 

 duces a flame or light. Oxidation, either rapid or slow, may take 

 place wherever there is uncombined oxygen. This fact has great 

 significance in the understanding of important problems of biol- 

 ogy. An example of slow oxidation is seen in the rusting of an 

 iron nail. If the rust and nail are weighed, the total weight 



Apparatus for separating water into hydro- 

 gen H and oxygen O: c, copper wire, p, plati- 

 num wire soldered to the copper, with insula- 

 tion so that no copper is exposed in this tube. 

 A few drops of sulphuric acid should be added 

 to the water, to facilitate the action of the 

 electric current. 



