34 CHEMISTRY OF FARM PRACTICE 



Preparation. Although oxygen exists at hand in enor- 

 mous quantities in a free condition in the air, yet it is 

 easier to obtain it by decomposing some of its compounds 

 than to try to separate it from the nitrogen with which 

 it is mixed in the atmosphere. In the chemical laboratory 

 it may be produced by heating in a test-tube a little of the 

 white salt, potassium chlorate (KQOs). This melts at 

 a comparatively low temperature (360 C.) and soon begins 

 to boil, yielding an abundant supply of oxygen. This 

 decomposition takes place at a still lower temperature 

 (200 C.) when the black mineral, pyrolusite (manganese 

 dioxide) is mixed with the potassium chlorate in the pro- 

 portion of three parts of the chlorate to one part of the 

 pyrolusite. The method of producing and of collecting 

 the gas is shown in Fig. 6. 



30. Hydrogen. The element hydrogen is a colorless 

 gas. Very little is found in a free condition, although a 

 small amount, estimated as one part in thirty thousand, 

 exists hi the ah 1 . It is not so active chemically as oxygen, 

 forming compounds with comparatively few of the other 

 elements. 



Occurrence. Some of the compounds of hydrogen are 

 of great importance. The principal source of hydrogen is 

 water, of which it constitutes about 11 per cent. It is an 

 essential ingredient of animal and plant structure. Organic 

 substances, such as starch, sugar, albumen, and fat; bodies 

 formed from organic matter, such as petroleum oil, bitu- 

 minous coal, and coal tar, and the vast number of hydro- 

 carbons, such as marsh gas, and acetylene, and the alcohols, 

 all are made in part of hydrogen. All acids and all bases 

 contain hydrogen as an essential ingredient. Ammonia 

 and its compounds, which form an important food for 

 plants, contain hydrogen. 



Preparation. Hydrogen, as well as oxygen, may be 

 obtained by the electrolysis resulting when an electric 

 current is passed through water. In order that the elec- 



