10 



STUDIES IN PHYSIOLOGY 



strated by holding a dry tumbler over a flame of burning 

 hydrogen. 1 The gas combines with oxygen, and drops of 

 moisture collect on the inside, as we noticed when the match 

 wood was burned. Water, therefore, may be called an oxid 

 of hydrogen. 



Oxidation. Since oxygen is always necessary for the 

 ordinary processes of burning, to this chemical action is 

 given the general name, ox-i-da'tion. It may take place 

 slowly, as is the case when we rub a match tip over our 

 fingers, 2 or rapidly, as when we scratch a match on sand- 

 paper. In any case oxidation means the chemical union of 

 oxygen with some other substance. It is always accompanied 

 by a certain amount of heat, and often, as in the burning of 

 a match or a candle, by light. 



Air, as we shall soon learn (p. 13), is not a chemical com- 

 pound, but a mixture of two gases ; for these gases do not 

 form a chemical union. 



Most of the facts in the preceding paragraphs may be 

 summarized in the following outline : 



THE BURNING OF A MATCH 



Materials in a Match + Oxygen in Air 



1. Phosphorus on the tip -f Oxygen 

 (yellow, waxy, solid) 



2. Sulphur on the tip 

 (yellow powder) 



+ Oxygen = 



+ Oxygen = 



3. Hydrogen in wood 



(colorless, odorless, 

 tasteless gas) 



4. Carbon in wood -f- Oxygen 



(black, brittle, solid) 



5. Mineral matter in wood 



(white or gray powder) 



= Compounds Formed 



Oxid of phosphorus 

 (white fumes of peculiar 

 odor) 



Oxid of sulphur 



(invisible gas of suffocat- 

 ing odor) 



Oxid of hydrogen (water) 

 (colorless, odorless, taste- 

 less liquid) 



Oxid of carbon (carbon di- 

 oxid) (colorless, odor- 

 less, tasteless gas) 

 Ash left after burning 

 (white or gray powder) 



1 See " Laboratory Exercises," No. 5. 



2 Rusting of iron is a good example of slow oxidation. 



