iv SUBSTANCES OF A LEAF 35 



ashes, boil them in water, filter, and then boil the 

 water away. A white powder will be left, which is 

 potash or pearl ashes. 



(2) The Phosphoric Acid can be easily recognised 

 in the ash by the following experiment : 



Experiment 23 



Warm the ash with a little strong nitric acid, add 

 a little water, filter, add a little more strong nitric 

 acid, and some molybdate of ammonia, and warm 

 the liquid gently. A yellow powder is slowly formed 

 in the liquid, thus indicating the presence of phos- 

 phoric acid. 



Warm in a test-tube in the same way a little phos- 

 phate of soda (which contains phosphoric acid), with 

 nitric acid and molybdate of ammonia, and the 

 same yellow powder will be formed. 



While these two substances (potash and phosphoric 

 acid) are quite necessary for the plant, they exist in 

 an available form in very small quantities in the soil, 

 and have therefore often to be supplied in manure 

 of different kinds. 



For instance, place a little dried horse dung on 

 the platinum foil and heat it strongly. Some ash is 

 left. On testing this in the way already explained 

 (in Experiments 22, 23), it will be found to contain 

 both potash and phosphoric acid. 



Potash is also often supplied in the form of kainit, 

 sulphate of potash, wood ashes, ashes of plants and 



