28 FOOD MATERIALS AND HOW TO DETECT THEM 



13. WATER 



Object. To detect the presence of water in a food. 

 Apparatus. Various substances, such as cereals, meats, etc., 

 test tubes, and a lamp or Bunsen burner. 



Method. Place the substance to be tested in a dry test 

 tube and hold it over the flame for a minute. What collects 

 on the inside of the tube ? Continue to heat the tube, turn- 

 ing it in a slanting position. 



Conclusion. The presence of water may be detected 

 by what means? 



Note. The steam which comes off at first is clear and condenses 

 into water, but the water that comes off later is stained more or less 

 by the products of destructive distillation of the substance used. 

 To prove that it is actually water that comes off, put a drop of it 

 on a little copper sulphate that has been heated until it has lost 

 its blue color and become white. The copper sulphate will return 

 to its former blue color. This test is not necessary in ordinary ex- 

 periments. 



Note. Some mineral substances are destitute of water. Such 

 substances are known as anhydrous, a word which means without 

 water. Such substances are very rare. When a substance is 

 deprived of its water, it is said to be dehydrated. Most such sub- 

 stances, if left to themselves, tend to absorb water and become 

 hydrated. This is illustrated in the behavior of lime when it be- 

 comes slaked. 



14. AMOUNT OF WATER 



Object. To find out the amount of water in different 

 articles of food. 



Apparatus. A slow oven, and any article whose water content 

 is to be determined, such as potato, radish, leaves of cabbage, etc. 



Method. Weigh *the article carefully, then chop it 

 fine and put it in an evaporating dish. Set it in a slow oven 



