LECTUKE. 



OXYGEN AND ITS COMBINATIONS 



BY PROF. GEO. J. CHACE, 



OF BROWN UNIVERSITY. 



Combustion or the rapid union of bodies witb oxj^gen^ attended witii 

 the free evolution of light and heat, takes place only at temperatures 

 more or less elevated. Phosphorus, the substance most readily ig- 

 nited, does not kindle till it has been raised to 120° Fahrenheit. Sul- 

 phur, the next most inflammable body, must be raised to the tempera- 

 ture of 300° before it will begin to burn. Charcoal kindles only at 

 the full red heat. Anthracite coal requires a temperature somewhat 

 higher ; while iron and most of the other metals must be brought to 

 the glowing white heat before they will enter into combustion. 



As tliis rapid union of bodies with oxygen takes place only where 

 their affinities have been energized by rise of temperature, it rarely 

 occurs in nature ; never, in fact, except where the lightning falls 

 upon the forest or the prairie, or the volcano sends forth its burning 

 streams of lava. As ordinarily witnessed, it is brought about by 

 artificial means for the attainment of economical and industrial ends. 



In order that oxygen may unite with bodies at ordinary tempera- 

 tures, it must be presented to them in connexion with water. Dry 

 oxygen, whether pure or mingled with nitrogen, as in the atmospheric 

 air, has no action upon them. With the single exception of potassium, 

 all the metals may be exposed to it for an indefinite length of time 

 without alteration . The most porishable organic substances in like 

 manner remain unchanged in it. Neither do these bodies suffer 

 change in water from which the air has been removed ; but, exposed 

 to the combined action of air and water, or rather to the action of air 

 dissolved in water, all organic substances and nearly all the metals 

 pass more or less rapidly into the state of oxides. It is in this way 

 that oxidation in nature is universally effected. 



The solvent powers of water are scarcely greater for solids than for 

 gases. Of some of these it absorbs several hundred times its volume. 

 For oxygen and nitrogen, however, the two principal constituents of 

 the atmosphere, its affinity is less energetic. Of the former, it ab- 

 sorbs but 4^ per cent. ; and of the latter, only 2^ per cent, of its vol- 

 urne. On account of the greater solubility of the oxygen, the air ob- 

 tained from water is richer in this element than ordinary atmospheric 

 air._ This contains only about 20 per cent, of its volume of oxygen ; 

 while the air extracted from water contains more than 30 per cent, of 

 its volume of oxygen. 



