STOEINCx OF SUPEEPHOSPHATE. 117 



lixed on the floor on the side opposite the discharge. During mix- 

 ing the superphosphate as it comes from the mixer adheres as an 

 immense cake to the bars of the cradle. To shift it, it suffices by 

 means of the winch to bring the cradle out of the den, where the 

 product is collected in trucks. The workmen have only to detach 

 what adheres to the bars and to let it fall into the trucks, by means 

 of rather long tools, so as to keep at a suitable distance. A hood 

 connected with a fan is placed on the discharge door, so that the 

 fumes are drawn from the exit of the " dens " and cannot inconveni- 

 ence the workmen. The superphosphate is then conveyed by wagons 

 into the Persian wheels which elevate it into the drying ovens. ^ A 

 fan draws vapour and dust from the dryers, and propels the first 

 into a condensation tower and the second into a dust chamber. 

 The manufacture of superphosphate, owing to these new arrange- 

 ments, presents no serious drawbacks as regards the health of the 

 workmen or of the neighbourhood. 



Breaking up and Si/ting or ScreeniJig of Super j^hosphate. — 

 The superphosphate placed in a heap in the fresh state consolidates 

 itself so much that it has to be broken down or "got" by the pick 

 and shovel. In order to get it to a proper degree of fineness, it was 

 formerly projected against an inclined sieve (screen) and the " core " 

 crushed with the back of the shovel. This sieve, of 6-8 mm. in 

 section, that is a quarter inch sieve, is still in use in small factories. ^ 

 Shaking and regulating sieves are also in use. To get the super- 

 phosphate from the heap, the best plan is to attack it at the tail 

 corner by drawing it towards oneself with the pick. By lifting it 

 in successive layers it would run the risk of being compressed. 

 Care is taken not to excavate underneath when the heap is more 

 than 6 ft. high.- 



Compact superphosphate is reduced to a pulverulent state by 

 Carr's disintegrator or a crusher fitted with steel teeth. 



Carr's Dismtegrator. — This disintegrator was invented by 

 Thomas Carr of Montepelier, near Bristol, and patented in Great 

 Britain. It consists essentially of two, four, six, or eight concentric 

 cages, the cylindrical sides of which consist of metallic bars h, 



1 Well-made superphosphate does not require to be put through quite 

 so tine a screen as a one-fourth inch screen except for the dry mixing of com- 

 pound manures. Good made superphosphate passed through an inch screen 

 is fine enough for most purposes, and through half an inch for all purposes, and 

 the price is now cut so fine that to add to the cost by passing it through a 

 needlessly close sieve is irrational, the more so as superphosphate, as dis- 

 tinguished from wet mixed compound manures, has little or no core. It only 

 wants a touch with the shovel to break it up to fine powder. — Tk. 



'^ But that is exactly what the man who gets the manure with the pick does. 

 He knows the right time to stand clear, and only the undermined portion falls, 

 and that quite gradually and without undue precipitation.— Tf. 



