COMPOUND MANURES 83 



necessary to use - =24.4 kg. sulphate of am- 



20.5 



100 x7 5 



monia. = 20.3 kg. of potash salt and con- 



o .0 



sequently 55.3 kg. of superphosphate testing 



100 X9 



= 16.27 per cent of phosphoric aicd. Ten 

 oo.o 



tons of the sulphate of ammonia used would there- 

 fore give 41 tons of the compound manure. It 

 would thus be necessary to use 31 tons of potash 

 salts plus superphosphate, say 8.32 tons of the 

 first, and 22.68 of the second. These manure 

 mixtures find an outlet chiefly in regions where the 

 vine, tobacco, the hop, and vegetables for preserves 

 are cultivated. They are likewise esteemed for 

 the culture of the sugar beet, barley, and potatoes. 

 Mixtures of superphosphate and potash salts 

 become readily moist in the store, so that they 

 cannot be prepared a long time in advance. 

 The use of calcined salts prepared from the 

 waste of potash factories, have the drawback that 

 they generally contain magnesium chloride. When 

 they are dried with precaution at 100 C. they 

 are free from basic magnesium compounds. The 

 retrogradation of the soluble phosphoric acid 

 in mixed manures under the action of the basic 

 salts of potash have been studied. By treating 

 salts of potash in the reverberatory furnace 

 to partial fusion, at about 800 C., the magnesium 

 chloride which they contain is decomposed by its 

 water of crystallization. A molecule of magnesia 



