PLANTS 



there is left a small residue of ash, amounting to about 5 per 

 cent, or less, of the dried substance. 



65. The ash consists chiefly of the following mineral sub- 

 stances, viz.: Potash, soda, lime, magnesia, phosphorous, 



FIG. 5. Experiment to determine the composition of vegetable tissue. A 

 simple apparatus, consisting of test-tubes, glass tubing and cork stoppers, is 

 fitted up as shown in the figure. The tube A should be of hard glass. A piece 

 of dry wood (W) is then heated over a burner, at first gently, then more vigorously, 

 until it is reduced to charcoal. At first water is driven off and condenses in the 

 cold tube CB). Then other volatile substances pass over, some of which con- 

 dense in B and others escape at C. The latter may be tested for H 2 O and CO 2 . 

 The jet escaping at C may then be ignited and the flame tested for H 2 O and 

 CO 2 . The liquid which has collected in the tube B, is wood vinegar and contains 

 water, acetic acid, wood alcohol and tar. Test with litmus paper for acid. 

 Then heat until it boils, when a blue flame may be obtained at C. This is due 

 to the volatilized alcohol. 



sulphur, silica, chlorine, and manganese, which are evidently 

 derived from the soil and must therefore have been absorbed 

 by the roots. 



66. Plants will thrive if the water supplied to the roots con- 

 tains only the above minerals and a trace of iron. But the 



