214 CHEMICAL MANUEES. 



by four crushers is carried to a weighing machine roanipulated by 

 a man of trust ; the latter registers the production of each crusher, 

 takes a small sample from each bag which he examines by the feel 

 and the sieve and runs it into a box installed for the purpose, or 

 each chief grinder weighs his product and is himself responsible for 

 the good execution of his work and its bagging up. Then the sacks 

 are carried to the depot. As in the slack season orders must be 

 executed from stock, it is necessary to use very sound and carefully 

 sewn bags and to preserve them full in a dry place, because gi^ound 

 basic slag, owing to its high lime content, is apt to solidify in a damp 

 place. The moistened powder cakes and cannot be rendered friable 

 by ignition as one might suppose ; it only becomes harder. The 2 

 cwt. bags (220 lb.) measure 50 x 90 cm. (say 20 x 36 in.). Even 

 in using sound bags some of them rot when stored full. That is 

 why basic slag is stored in iron silos. 



It has already been mentioned that the cooling of basic slag is 

 accelerated by quenching with water. This work is not without 

 danger. When basic slag solid on the outside but incandescent 

 inside is exposed to the shower of water, this may penetrate into 

 the inside of the block by cracks and crevices ; it is converted 

 into steam which occupies a volume 1600 times greater at 0^ C. and 

 7500 times greater at 1000° C. When such steam is given off in- 

 stantaneously a very small quantity of water suffices to cause an 

 explosion. It may also happen that a block of basic slag still liquid 

 inside may have an escape, which is particularly dangerous for the 

 workmen. It is necessarv therefore to draw their attention thereto. 

 Finally, gas may form inside the basic slag withoiit exterior aid, 

 which, in virtue of its tension, seeks a vent, and not finding any 

 causes the block to fly away in pieces. When a crusher has to be 

 repaired, and if the repairs cannot be done on the spot, it is con- 

 veyed to the forge on a rolling crane or on a truck running on rails. 

 Crushing being a work which requires to be continuous, they are 

 not stopped except for dinner at noon, otherwise they work 

 continuously, the workmen replacing each other at lunch time. 

 During the dinner hour the machines are inspected and thei bearings 

 lubricated. The grinding plant should be simple. Owing to the 

 peculiar nature of the substance being ground, conveyors and 

 mechanical feeders are not applicable. A crusher of 2 metres 

 (6^ feet) can produce 15 tons in 10 hours of ground basic slag, when 

 the basic slag is fresh cooled and not too hard. P. Mellman, of 

 Berhn, German patent 107,234, projects a jet of steam or air into the 

 liquid basic slag at the moment it is discharged by the couvertor. 

 The basic slag then becomes friable, and is very easily ground. 

 The basic slag in blocks is sold to the grindiug factories according 

 to their percentage of phosphoric acid. The determination is 

 generally made on the powder produced during crushing, supposing 



