162 



COMPOSITION OF THE PHOSPHATES 



questions-as to the relation which potash and soda bear to the 

 healthy life of the plant, and as to their power of taking the 

 place of each other. This latter inquiry is one which is deserv- 

 ing of extended and special attention ; and I shall have occasion 

 to revert to it in a subsequent chapter. 



6. Their effects, in comparison with those of equivalent 

 quantities of the sulphates of potash and soda, and of the chlorides 

 of potassium and sodium. This series will determine whether 

 they owe their influence upon the soil or the plant merely to 

 the alkali they contain ; or whether the special properties pos- 

 sessed by this alkali in its state of carbonate may not determine 

 the nature and extent of its influence. 



7. Lastly, as these carbonates exercise a special action on the 

 organic matter of the soil, in hastening its decomposition and 

 rendering it soluble, I would suggest experiments as to their 

 action on peaty soils on dry moorish soils, rich in inert vege- 

 table matter and generally on soils called deaf, sleepy, silly, &c. 

 On such soils lime very frequently produces beneficial effects, 

 and I think it not unlikely that poor corn on such soils might 

 be renovated by a top-dressing of these carbonates, applied in 

 the early growing-time of spring. 



4. Composition of the phosphates of potash and soda. 

 1. Phosphate of potash. Two varieties of phosphate of 

 potash are known. They consist respectively of 



Potash, . . 56.94 

 Phosphoric acid, . 43.06 



100 



Potash, . . 34.40 



Phosphoric acid, . 52.48 

 Water, . . 13.12 



100 



2. The phosphate of soda of the shops consists of- 



Soda, . 

 Phosphoric acid, 

 Water, 



17.88 

 20.40 

 61.72 



100 



These phosphates are prepared by treating an excess of 



