MANUFACTURE OF NITRATE OF SODA. 



281 



The caliche is extracted in the following manner: — A shaft 

 about 1 foot in diameter is sunk. Into this a boy is lowered, 

 who forms a recess at the bottom :'n the shape of an inverted 

 funnel, which is filled with a slow blasting powder (as shown 



^^^ 



in the above Fig.) made on the works, and is ignited by one 

 ordinary fuze. This causes a dull explosion, breaking and loosen- 

 ing the ground around the shaft for a radius of about 10 yards. 

 The overlying stratum of hard rock, porphyry, gneiss, &c., locally 

 known as "costra," is removed, and the caliche extracted and 

 split and broken by sledge hammers, steel wedges, and bars, into 

 blocks of about 30 lbs. weight. It is then loaded in the cars 

 and carried into the crushing machines, and there broken into 

 cubes of about 2 inches. The three crushing machines are 

 driven by a 25 HP. Tangye engine. 



Cars stand under the mouths of the crushers to receive the 

 broken caliche, and these when fully loaded are hauled up to the 

 turntable by the winding-engine, and from there shoved on and 

 the contents tipped into the boiling tank in course of being 

 charged. The turntable is not in the centre of the six sets of 

 rails serving the twelve boiling tanks with the side tip cars, but 



