CHAPTER IV 

 THE MANUFACTURE OF FOODS AND FUELS 



The Annual Value of Food. — Since food is indis- 

 pensable, its value cannot be adequately represented in 

 definite terms. It constitutes the largest item in com- 

 merce. The food produced in California alone in 1919 

 was worth, in round numbers, $500,000,000; that pro- 

 duced in the United States, $15,000,000,000; and in the 

 whole world an inconceivably large sum. 



Annual Production of Food Necessary. — There is 

 no store of food in nature as there is of water; there is 

 no fixed amount, for it is annually manufactured from the 

 raw materials, in green plants. The quantity varies, 

 both in the wild state and under cultivation, from year 

 to year. There is rarely any considerable excess; there 

 is frequently shortage; there is generally enough. Man 

 and a few other animals harvest and store food for future 

 use, but the surplus of supply over demand is generally 

 very slight, and locally may not exist at all. The result 

 of shortage is at times disastrous. 



The Food Materials. — The food materials, some- 

 times erroneously spoken of as plant food, are carbon 

 dioxid (CO2), a gas, water (H2O), a liquid, and mineral 

 salts, solids. Carbon dioxid occurs in the air in very 

 dilute proportions, two hundredths of one per cent 

 (0.02%) on the average. In spite of its extraordinary 

 dilution the total amount in the earth's atmosphere is 

 enormous. Because of the constant contributions to 

 the atmosphere from a variety of sources, of which 

 perhaps ordinary combustion is the most easily under- 

 stood, this amount and proportion are maintained. 



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