THE NONMETALLIC MINERALS. 207 



with ease. The salt is then blasted down from the overhanging body. 

 The yearly output is about 50,000 tons. 



The salt as it comes from the mine is dumped into corrugated cast- 

 iron rolls, which crush it. Next it goes into revolving screens, which 

 take out the coarser lumps for "crushed salt" and let the fine stuff 

 pass to the buhrstones. These grind the salt, and from them it goes 

 to the pneumatic separators, which take out the dust and separate the 

 market salt into various grades. Taking the dust out is essential to 

 the production of a salt that will not harden, since the fine particles of 

 dust deliquesce readily and on drying cement the coarse particles 

 together. The drill used in the mine is what is known as the "Russian 

 auger." It is turned by hand and forced by a screw of 12 threads per 

 inch. The holes take cartridges H inches diameter. Two men will 

 bore 75 feet of hole each working-day of eight hours. Three-quarters 

 of a pound of 18 per cent dynamite is used to the ton of salt mined. 



On the Colorado Desert the salt occurs in the form of a crust a foot 

 or more in thickness, resting on a lake of shallow brine. This crust, 

 which is covered with a thin layer of dust and sand blown over it from 

 the surrounding desert, is cut away longitudinally, much as ice is cut 

 in the North. When loosened, the block, falling into the water beneath, 

 is cleaned of its impurities, and is then thrown out on a platform to 

 dry, after which it is ground and packed for market. In many parts of 

 the arid West the salt is obtained merely by shoveling up the impure 

 material deposited by the evaporation of salt lakes and marshes during 

 seasons of drought. In this way is obtained a large share of the 

 material used in chloridizing ores. 



In the preparation of salt from sea water, solar evaporation alone 

 is relied upon nearly altogether. This method, like the next to be 

 mentioned, depends for its efficiency upon the fact already noted that 

 sea water holds in solution besides salt various other ingredients, 

 which, owing to their varying degrees of solubility, are deposited at 

 different stages of the concentration. In Barnstable County, Massa- 

 chusetts, it was as follows: A series of wooden vats or tanks, with 

 nearly vertical sides and about a foot in depth, is made from planks. 

 These are set upon posts at different levels above the ground, and so 

 arranged that the brine can be drawn from one to another by means 

 of pipes. Into the first and highest of these tanks, known as the 

 "long water room," the water is pumped directly from the bay or 

 artificial pond by means of windmills, and there allowed to stand for 

 a period of about ten days, or until all the sediment it may carry is 

 deposited. Thence it is run through pipes to the second tank, or 

 "short water room," where it remains exposed to evaporation for 

 two or three days longer, when it is drawn off into the third vat, or 

 "pickle room," where it stands until concentration has gone so far 

 that the lime is deposited and a thin pellicle of salt begins to form on 



