COMPOSITION OF LIFELESS AND LIVING THINGS 18 



17. Oxidation is the chemical union of oxygen with some 

 other substance. It may take place slowly, as when carbon 

 is made to glow in the air ; or it may take place rapidly, as 

 when carbon bums in oxygen. But whenever oxidation takes 

 place, (1) an oxid is formed, (2) a certain amount of heat is 

 liberated, and (3) if the process is sufficiently rapid, light 

 is seen. 



III. A STUDY OF THE FOOD SUBSTANCES 



18. Introduction. The food substances needed by plants 

 and animals may be divided into five classes, namely: 

 (1) carbohydrates (i.e. starches and sugars) ; (2) fats and oils; 

 (3) proteins, 1 which are also known asjdbuminous or nitrog- 

 enous substances (e.g., white of egg, lean meat, gluten of 

 wheat) ; (4) minerals (e.g. common salt, saltpeter, phosphate 

 of lime) ; (fy^wafer. 



19. To determine the chemical composition of starch. 



Laboratory Study No. 6. Suggested as home work. 



Warm some starch in an old cooking spoon in order to 

 drive off any water that may be in it, but do not allow it 

 to burn. To determine when the starch is free from water, 

 hold the heated starch under a dry, cold tumbler, and if no 

 moisture collects upon the tumbler, the starch contains no 

 water. Now set the starch on fire, and hold a cold, dry 

 glass over the burning starch. 



1. Tell what you have done and state what is formed on the 



inside of the tumbler by the burning of the starch. 



2. What is the only chemical element that could possibly 



form water by burning (i.e. by uniting with oxygen) ? 



3. What chemical element, therefore, must have been pres- 



ent in the starch in order to have produced water when 

 dry starch is burned? 



1 The term protein is used throughout this book instead of proteid, 

 because of the unanimous recommendation in favor of the former 

 term by the American Society of Biological Chemists and the 

 American Physiological Society. See Science, April 3, 1908. 



