CHAPTEE VII. 



CRUSHING, SIFTING, DRYING, AND STORING OF SUPERPHOSPHATE. 



RETROGRADATION. 



Emptying and Shifting the Sujjerphosphate House or " Den " — 

 Emptying the superphosphate "den" is still done in a primitive 

 manner, which consists in charging the superphosphate with the 

 shovel into the receiving vessel of an elevator or into half-ton 

 wagons.^ The latter are run towards a crane that lifts them and 

 spreads their contents over the heap from a certain height. In 

 default of the elevator the heap could not be raised high enough 

 and more capacious warehouses would be required. 



Another method of shifting the superphosphate out of the houses, 

 consists in emptying them from below. In that case the house is 

 built over a sort of cellar, in which the material drops on to an end- 

 less belt 20 in. wide, through holes in the floor covered by iron lids. 

 The belt drops the superphosphate on an inclined plane ending in the 

 receiver of an elevator, which discharges the superphosphate either 

 on the heap or into a Carr's disintegrator, or into a jigger, according 

 to the method of working adopted. The best plan is to give the 

 elevator a certain slope and use comparatively large cups, because 

 fresh superphosphate ought to be j)ressed as little as possible, other- 

 wise it is converted into a gluey mass difficult to manipulate and to 

 dry. The emptying of the superphosphate " den " is not exactly a" 

 pleasant job, even if the heat and the gases, still persistent there 

 und disengaged when the superphosphate is displaced, be not taken 

 into account. The workmen are therefore obliged to work with 

 aspirators, the sponge of which they should keep moist, so as to 

 prevent any accident. The superphosphate ought to be extracted 

 from the chamber whilst it is still hot, so that the vapour may be 

 eliminated and not condense by cooling. If the superphosphate 



1 T^;i But in working even on a fairly large scale, in Great Britain the 

 work of shifting is sometimes still done by barrow, plank, and gang sack. One 

 man " gets " the stuff with the pick, two men fill the barrow, a fourth or fifth 

 man, if need be, wheels it on the ground at first, then up a plank, and when the 

 plank is too steep the barrow men cease to ply their barrows and take to gang 

 sacks, their heads and shoulders being protected by a " backing " cap or at a 

 pinch by a sack. — Tr. 



(HI) 



