22 BOTANY 



Proteids. — Nitrogenous foods, or proteids, contain the element 

 nitrogen in addition to carbon, h3'drogen, and oxygen of the car- 

 bohydrates and hydrocarbons. They include some of the most com- 

 plex substances known to the chemist, and as we shall see, have a 

 chemical composition very near to that of living matter. Proteids 

 occur in several different forms, but the following tests will cover 

 most cases commonly met. White of egg, lean meat, beans, and peas 

 are examples of substances composed in a large part of proteid. 



Place in a test tube the substance to be tested; for example, a bit of hard- 

 boiled egg. Pour over it a little strong (80 per cent) nitric acid. Note the 

 color that appears — a lemon yellow. Now wash the egg in water and add a 

 little ammonium hydrate. The color now changes to a deep orange, show- 

 ing that a proteid is present. 



If the proteid is in a liquid state, its presence may be proved by heating ; if 

 it coagulates or thickens, as does the white of an egg, when boiled, then 

 proteid in the form of an albumen is present. 



Another characteristic proteid test easily made at home is by burning 

 the substance. If it burns with the odor of burning feathers or leather, 

 then proteid forms part of its composition. 



Books for Reference 

 for the pupil 



Avery-Sinnott, First Lessons in Physical Science. American Book Company. 

 Eddy, Experimental Physiology and Anatomy. American Book Company. 

 Hunter and Valentine, Laboratory Manual of Biology. Henry Holt and Company. 

 Peabody, Laboratory Exercises in Anatomy and Physiology. Henry Holt and Com- 

 pany. 



FOR THE TEACHER 



Foster, A Text-hook of Physiology. The Macmillan Company. 



Green, Vegetable Physiology. J. and A. Churchill. 



Sedgwick and Wilson, General Biology. Henry Holt and Company. 



