80 MANUFACTURE OF FERTILIZING MATERIALS 



big heap in the warehouse for the ingredients to 

 combine. 



Mixtures of superphosphate and sulphate of 

 ammonia exhibit phenomena of a peculiar nature. 

 They gradually heat and become damp to the 

 touch; they dry again, and owing to the forma- 

 tion of gypsum, they harden more and more. 

 The reaction lasts for a variable time. It depends 

 on the nature of the superphosphate and its man- 

 ner of manufacture, and may end in fifteen days, 

 when the mass is in a large heap and exposed to a 

 certain pressure. Superphosphate of ammonia 

 forms a hard rocky mass, the shifting of which is 

 expensive, for one is obliged to blow it up with 

 gunpowder. However, only neglect of the man 

 in charge of the mixer in not running in the proper 

 amount of acid would produce this. It is then 

 crushed by a disintegrator, is passed through the 

 sieve, and bagged up immediately afterwards, for 

 it does not solidify again if made according to rules, 

 that is to say, if each grain of sulphate of ammonia 

 is united to its grain of superphosphate to form a 

 sulphophosphate. To diminish the hardening as 

 much as possible, sand or better still powdered 

 peat, sawdust, wool dust or chimney soot are 

 added, and in the second place, immediate satura- 

 tion of the sulphate of lime by the addition of a 

 little water. The second grinding is therefore 

 necessary to effect the perfect mixing of the two 

 ingredients. In fact, if the substance be analyzed 

 after the first crushing, there will be found 8.8 



