24 AGRICULTURAL ANALYSIS 



cess of base should be added to convert the acids into sulfates or 

 phosphates. 



Where the samples contain no ingredient capable of attacking 

 aluminum, they can be conveniently dried, in circular dishes of 

 this metal about seven centimeters in diameter and one centi- 

 meter deep, to constant weight, at the temperature of boiling 

 water. 



32. Moisture in Monocalcium Phosphates. In certain fertilizers, 

 especially superphosphates, containing the monocalcium salt, the 

 estimation of water is a matter of extreme difficulty on account 

 of the presence of free acids and of progressive changes in the 

 sample due to different degrees of heat. 



Stoklasa has studied these changes and reaches the following 

 results : 12 



A chemically pure monocalcium phosphate of the following 

 composition, viz., 



CaO 22.36 per cent. 



P 2 5 56.67" 



H 2 21.53" 



was subjected to progressive dryings. The loss of water after 

 10 hours was 1.83 per cent.; after 20 hours, 2.46 per cent.; 

 after 30 hours, 5.21 per cent. ; after 40 hours, 6.32 per 

 cent; after 50 hours, 6.43 per cent. The loss of water 

 remained constant at 6.43 per cent. This loss represents one 

 molecule of water as compared with the total molecular magni- 

 tude of the mass treated. A calcium phosphate, therefore, of 

 the following composition, CaH 4 (PO 4 ) 2 .H 2 O loses, after 40 

 hours drying at 100, its water of crystallization. The calcium 

 phosphate produced by this method forms opaque crystals which 

 are not hygroscopic and which give, on analysis, the following 

 numbers : 



CaO 24.02 per cent. 



P,0 6 60.74" " 



H,0 15.00 " " 



The temperature can be raised to 105 without marked change. 

 " Zeitschrift fur analytische Chemie, 1890, 29 : 390. 



