76-78] PHOSPHATIC MANURES 3 1 



air on gas-lime is to turn the calcic sulphide (CaS) to gypsum 

 (CaS0 4 ). The heating with charcoal brings about the 

 opposite effect, i.e. reduces the gypsum to calcic sulphide. 



Potash Manure 



76. Potash in Kainit— Kainit is the most common 

 potash manure. To show that it contains potassium, place 

 a little kainit on a watch-glass and moisten it with dilute 

 hydrochloric acid. Test this substance in the flame as 

 directed on page n. The flame will appear yellow, due to 

 sodium present as an impurity. Now observe the flame 

 through an indigo prism or a piece of cobalt-blue glass. It 

 will appear crimson. This is a distinctive test for potash 



(189). 



Phosphatic Manures 



77. Phosphoric Acid. — This generally occurs in 

 artificial manures as a phosphate of lime. These phosphates 

 are four in number, and each has its own distinctive 

 properties. Their chemical names and formulae are as 

 follows : — 



a. Monocalcic phosphate . CaO.(H 2 0) 2 .P 2 5 



b. Bicalcic phosphate . (CaO) 2 .H 2 O.P 2 5 



c. Tricalcic phosphate » (CaO) 3 .P 2 5 



d. Tetracalcic phosphate (CaO) 4 .P 2 5 



Their commercial names are — 



a. Superphosphate of lime. b. Reverted phosphate. 



c. Bone or mineral phosphate, d. Slag phosphate. 



The properties of slag phosphate are very similar to 

 those of reverted phosphate, so in the next three experi- 

 ments reverted phosphate is not considered, but it is referred 

 to in paragraph 81. 



78. Action of Water on Phosphates.— Into three 



