PRELIMINARY EXPERIMENTS XV 11 



wood decays, the carbon in it oxidizes (unites with oxygen) 

 and carbon dioxid gas is formed. When wood burns, the 

 oxidation is more rapid. When iron oxidizes, iron rust is 

 formed. When hydrogen is oxidized, water is formed, i 

 Kerosene oil contains hydrogen, and water is formed when 

 it is burned. Almost every one has noticed the cloud of 

 moisture which collects on the chimney when the lamp is 

 first lighted. By using a chimney which has been kept 

 in a cold place, the moisture becomes apparent; soon 

 the chimney becomes hot and the water no longer collects, 

 but it continues to pass into the room as long as the lamp 

 burns. Fats also contain hydrogen. Hold a piece of cold 

 glass or an inverted tumbler above the flame of a tallow 

 candle. Does water collect on it ? 



Oxidation may be said to be the basis of all life processes 

 for this reason : oxidation gives rise to heat and sets free 

 energy, and all living things need heat and energy in order 

 to grow and live. The heat of animals is very noticeable. 

 The oxidation in plants also forms a slight amount of heat. 

 In both animals and plants oxidation is much slower than 

 in ordinary fires. That heat is formed even in slow oxida- j 

 tion is shown by fires which arise spontaneously in masses 

 of decaying material. The rotting of wood is not only 

 accompanied by heat but sometimes by light, as when 

 " fox fire " is emitted. Rub the end of a match on your 

 finger in the dark. Explain the result. Strike a match 

 and notice the white fumes which rise for an instant. 

 These fumes are not ordinary smoke (particles of carbon), 

 but they are oxid of phosphorus. Why wilL water (oxid 

 of hydrogen) not burn ? Sand is oxid of silicon. Explain 

 how throwing sand on a fire puts it out. [See also experi- 

 ments with candle and breath, in Introduction to Human 

 Biology.] 



