A HARD-WORKING DIET. 337 



produce light. But it is hardly in accordance with the 

 popular use of the word to speak of an iron nail which 

 is rusting in the damp as " burning." There is this 

 more serious objection to employing the more familiar 

 word " burning " instead of " oxidation." People have 

 lately dropped into the habit of speaking of an electric 

 incandescent arc lamp as " burning " steadily or badly, 

 though this light does not depend on oxidation at " Oxidation " 



not always 



all. " Burning is then not always an equivalent for equivalent to 

 "oxidation." 



It is desirable to have a clear mutual understanding 

 about the use of this word " oxidation," as it will have 

 to be frequently used in the following pages. Oxida- 

 tion is the act of combining with Oxygen. All the 

 elements except Fluorine combine with Oxygen. The Oxygen is 

 Oxygen may come from the air of which, as mentioned, a ir and in 



., r r/vi i i , -, r combination 



it forms one-fifth by weight ; it may come from water in many 

 of which it forms eight-ninths by weight ; it may come com P ounds 

 from nitre of which it forms nearly one-half by weight 

 (for which reason it is used in making gunpowder,) ; it 

 may come from chlorate of potash of which it forms 

 two-fifths by weight, or permanganate of potash 

 (Condy's fluid) or from many other compounds. The 

 combination may be rapid as in the case of gas- 

 burning, or slow as in the case of the " tarnishing " of 

 kitchen coppers ; it may give rise to but little heat or 

 to dazzling light. In any case the combination with Oxidation, 



it seems, 

 oxygen is called oxidation, and OXIDATION, it seems, always gives 



ALWAYS GIVES RISE TO HEAT. The way in which n! 

 our life depends on this is spoken of on p. 347, &c. 



CARBON is perhaps generally felt to be more fami- Carbon. 

 liar than Oxygen as it can be seen. Fine particles 

 of it are a solace to the eyes of a weary man as 



VOL. I. H. Z 



