STUDY OF NUTRIENTS 



Phosphorus, sulphur, carbon, iron, oxygen, nitrogen, and 

 hydrogen are a few of the chemical elements to be found in 

 plant and animal bodies. These elements occur, however, 

 not as elements, but in combinations, or compounds. There 

 are many of these combinations, but they may be grouped 

 together under a few class names. These classes of com- 

 pounds show certain definite qualities by means of which 

 their presence may be detected. The classes are called "proxi- 

 mate principles J or nutrients. The most important are: 



Proteids, or nitrogenous compounds. 



Carbohydrates, or starches and sugars. 



Fats and oils. 



Mineral salts. 



Water. 



XIII. — ^Proteids. 



Apparatus. — Raw white of egg, olive oil, salt, nitric acid, ammonia, 

 Millon's reagent,^ caustic soda, sulphate of copper (blue vitriol), test 

 tubes. 



Directions. — A. Put a little white of egg (a good example 

 of proteid) in a test tube, cover with two inches of water, 

 and shake. Does the white of egg dissolve? Heat the 



^ To make Millon's reagent, mix one part of mercury by weight with two 

 parts of nitric acid (concentrated commercial) ; when the mercury is all dis- 

 solved, dilute with twice the volume of water. 



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