MANUAL OF GENEEAL AGEICULTUEE. 33 



PART III CHEMISTRY OF PLANTS. 



31. MOISTURE IN THE PLANT. 

 Materials: A small pan with a capacity of 100 to 

 150 c.c., a balance sensitive to 10 milligrams, drying oven, 

 thermometer. 



Dry the pan and weigh it carefully. Nearly fill it 

 with finely cut stems and leaves of a fresh plant that is 

 growing vigorously. Weigh again. Kecord all weights. 

 Get the weight of the plant material by the difference. 

 Place the pan in the oven and keep the temperature at 100 

 to 105 degrees C. for five or six hours. Cool and weigh. 

 Heat in the oven again for an hour and cool and weigh. 

 If the weight is constant, the material is dry. If there is 

 an appreciable difference shown by the two weighings, 

 repeat the heating, cooling, and weighing till a constant 

 weight is shown. The total loss in weight represents the 

 amount of water held mechanically in the plant. Calcu- 

 late the amount in per cent of the original weight of the 

 plant material. Our ordinary growing plants hold 75 to 

 95% of water in % this way. Save the dry material for 

 Exercises 32 and 34. 



32. COMPOSITION OF DRY MATTER OF PLANTS. 



Materials: Porcelain crucible, 250 c.c. flask, wire 

 triangle, iron tripod or ring stand. 



Nearly fill the crucible with dried plant material and 

 heat it over the burner till the substance begins to blaze. 

 Remove the burner and quickly hold over the blazing ma- 

 terial a flask, nearly full of cold water and clean and dry 

 on the outside. Note the condensation of water on the 

 cold surface of the flask. As the material used was dry, 

 this water must have been produced by the breaking up 

 of the plant tissues. It consists of oxygen and hydrogen, 

 two elements of plant composition. This, as well as the 

 mechanically held water, was derived from the soil water, 

 having risen through the roots. Remove the flask and ob- 

 serve the charred mass remaining in the crucible. It is 

 principally carbon derived from the air. Continue to heat 



