THE NONMETALLIC MINEBALS. 



211 



temperature within these chambers is very uniform, varying only 

 between 10 and 15 C. The air is dry and healthful. The miners hew 

 out of the salt statues of the saints, pyramids, and chandeliers, where 

 they can place 300 lights. One chamber, called the Chapel of St. 

 Antoine, with its altar, statues, columns, etc., is still in a condition of 

 perfect preservation after a lapse of two centuries. The statements 

 to the effect that the workmen, and indeed entire families, pass a good 

 share of their lives in these mines, almost never coming to the surface, 

 is stated by Brehm to be wholly erroneous. In reality, all the workers 

 leave daily, only the horse remaining below. 



The following statistics relative to the salt industry in the United 

 States, are taken from Rothwell's Mineral Industry, 1892, page 419: 



The total production of salt in the United States for 1899 amounted 

 to 19,861,948 barrels, or 2,780,677 short tons. 



Uses. The principal uses of salt have always been for culinary and 

 preservative purposes. Aside from these, it is also used in certain 

 metallurgical processes and in chemical manufacture, as in the prep- 

 aration of the so-called soda ash (sodium carbonate), used in glass 

 making, soap making, bleaching, etc. , and in the preparation of sodium 

 salts in general. Clear, transparent salt has been utilized in a few 

 instances in optical and other research work. Secretary S. P. Lang- 

 ley of the Smithsonian Institution, in his astrophysical work made use 

 of a salt prism some 19 centimetres in length and with faces 15 centi- 

 metres in breadth. 



