FOOD AND DRINK 73 



vegetable oils. Most of the breadstuffs contain more or 

 less fat. The fats and oils are rich in carbon and hydro- 

 gen but contain little oxygen. They are more valuable 

 than the starches and sugars as sources of energy, but the 

 latter are more easily digested. 



104. Mineral Salts. Besides the food stuffs which are 

 obtained from the animal and vegetable kingdoms, our 

 bodies must have a certain amount of mineral matter. 



The principal mineral foods are water, salt, iron, lime, 

 magnesia, phosphorus, and potash, which are present both 

 in vegetable foods and in meat. Except water and common 

 salt, the mineral substances usually enter the body only in 

 combination with other food stuffs. 



Some of the salts of food play an important part in 

 directing the chemical changes that take place in the 

 tissues of the body. Others give hardness to the bones 

 and the teeth. 



Experiment 26. To test cereals for fat. Mix an even teaspoonful 

 of Indian meal, oatmeal, or rye meal with an equal volume of ben- 

 zine. As its vapor is highly inflammable, the greatest caution must 

 be exercised not to handle it near a flame or a hot stove. Stir care- 

 fully and filter the mixture after it has stood for fifteen minutes to get 

 rid of the ether odor. Evaporate some of the filtrate on a watch 

 glass. A greasy residue is left, which may be shown by rubbing it 

 on a piece of tissue or rice paper. 



Experiment 27. Evaporate a small quantity of milk to dryness in 

 an open dish. After the dry residue is obtained, continue to apply 

 heat ; observe that it chars and gives off pungent gases. Raise the 

 temperature until it is red hot, then allow the dish to cool ; a fine 

 white ash will be left behind. This represents the mineral matter 

 of the milk, which does not burn. 



The preceding experiment shows that a great part of milk is made 

 up of water. The residue is the solid substance. The loss of weight 

 is due chiefly to the loss of water. 



