COMPOUND MANURES. 147 



the same way. Suppose it is desired to prepare a mixture of this 

 nature with 5 per cent of nitrogen, 7 '5 per cent of potash, and 9 per 

 cent of phosphoric acid, and that there was to he used for the j)ur- 

 pose sulphate of ammonia wdth 20*5 N, and potash salts with 

 37 per cent K. To get 100 kg. of superphosphate of ammonia and 

 potash it is therefore necessary to use : — 



— ^7^^— = 24-4 ks. of sulphate of ammonia. 

 20-O 



^^i^^ — = 20*3 kg. of potash salt, and consequently 



5o'3 kg. of superphosphate testing. 



100 X 9 



— - = 16'27 per cent of phosphoric acid. 



OO'o 



Ten tons of the sulphate of ammonia used would therefore give 

 41 tons of the comi^ound manure. It would thus be necessary to use 

 31 tons of potash salt plus superphosphate, say 8-32 tons of the first, 

 and 22-680 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 super- 

 phosphate 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 ^orepared from the waste of potash factories, have the 

 drawback that they nearly always contain magnesium chloride. 

 When they are dried with precaution at 100° C, they are exempt 

 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 Emmerling as a result of 

 experiments thereon. By treating salts of potash in the reverbera- 

 tory furnace to partial fusion, about 800° C. (1472° F.), the mag- 

 nesium chloride which they contain is decomposed in the moist 

 condition as follows : — 



MgCl, + H.O = MgOHCl + HCl 



According to the equation — 



CaH,(PO,)-' + MgO = CaMgHiPOj- + H,0, 



a molecule of magnesia can retrograde a molecule of phosphoric 

 acid, from which it follows that one part of MgO can render 3-55 per 

 cent of phosphoric acid insoluble. If one use, for example, twenty- 

 been chemically replaced by equivalent proportions of ammonia and potash, 

 whereas it is a mere mechanical mixture of superphosphate with sulphate of 

 ammonia and potash salts. — Tn. 



