302 A YEAR IK SCIENCE 



added to a solution containing grape sugar and then 

 boiled, the color becomes brick red. 



Pats and oils. Under this class are included not only 

 what we ordinarily understand as fat, but also all 

 vegetable and animal oils. Like the carbohydrates, the 

 fats and oils contain only the three elements, carbon, 

 hydrogen, and oxygen, but in different proportions. 

 They have a much lower percentage of oxygen. They 

 are all lighter than water and insoluble in it. 



Test for fats and oils. The presence of fats may be 

 detected in one of two ways : 



(a) Put a small quantity of the substance to be 

 tested on a piece of paper and slowly heat it. If fat is 

 present, it will make a translucent grease spot on the 

 paper. 



(b) Fats are soluble in benzine and ether. The sub- 

 stance to be tested is soaked in benzine or ether. Then 

 it is filtered. If the solution is allowed to stand, the 

 ether will evaporate. Fat, if present, will then remain, 

 because it does not evaporate. 



Mineral salts or inorganic foods. Dissolved in ordi- 

 nary drinking water, in lean meat, and in vegetables 

 are many forms of salts. Only one, common salt, do 

 we add to our diet, All salts are unburnable. When 

 foods are burned, if ashes are left behind, we may 

 conclude that mineral matters are present. 



Water. Nearly 59% of the weight of our bodies is 

 water. Some water is taken into the body directly, 

 but much of it indirectly. A large proportion of most 



