34 THE FOOD OF PLANTS CHAP. 



The Ash contains many mineral Substances, 

 among -which Potash and Phosphoric Acid 

 are of Special Importance 



The ash of the plant contains some substances 

 necessary to the life of the plant and some that are 

 not necessary, as has been proved by experiments, in 

 which plants have been grown in water, in which 

 the various substances found in the ash, have been 

 dissolved. 



You cannot hope to understand the nature and 

 properties of all these different substances until you 

 are able to study a more advanced book than this. 



Let us, however, look at two of these substances, 

 and learn how we can recognise them, namely, Potash 

 and Phosphoric Acid. 



(1) The Potash, or " Pearl Ashes" as it is some- 

 times called, can be easily recognised by the following 

 experiment : 



Experiment 22 



Dip a fine platinum wire in some hydrochloric 

 acid and then in the ash, and then hold the 

 wire in the flame of a spirit-lamp. The flame is at 

 once coloured violet by the potash. Compare this 

 with the flame produced by dipping the wire into 

 the solution in water of a little potash obtained from 

 the chemists, and the same coloration is produced. 

 The potash can be easily separated from the ash 

 of the plant by boiling water. Take some wood 



