THE NCXPTMETALLIC MINEBALS. 209 



from the lake into ponds prepared for its reception and situated above the level of 

 the lake surface. The mother liquors flow off are returned to the lake, in fact 

 when the evaporation has reached the proper stage. From the establishment of the 

 works until 1883 the lake was close to the ponds; but, owing to the unusually high 

 rate of evaporation attending the dry seasons of the immediate past, the water has 

 receded, so that at present it has to be conveyed over 2,500 feet to the evaporating 

 receptacles. This is effected by the aid of two centrifugal pumps, raising together 

 14,000 gallons of water per minute. The pumps throw the water to a height of 14 

 feet into a flume, through which it flows to the ponds. These are nine in number, 

 and are arranged in series. In the first pond the mechanically suspended matters 

 are left as sediment or scum, and the water passes into the second in a clear condi- 

 tion. The ponds cover upward of a thousand acres, and the drain channels leading 

 from them aggregate 9 miles in length. The pumping continues through May, June, 

 and July. A fair idea of the rate of evaporation in the thirsty atmosphere of the 

 Great Basin may be gained from contemplating the fact that to supply the volume 

 of water disappearing from the ponds by evaporation requires the action of the pumps 

 ten hours daily in June and July. This is equal to the carrying away of 8,400,000 

 gallons per day from the surface of the ponds. 



The "salt harvest" begins in August, soon after the cessation of pumping, and con- 

 tinues till all is gathered, frequently extending into the spring months of the succeed- 

 ing year. An average season yields a layer of salt 7 inches deep, which amount 

 would be deposited from 49 inches of lake water. The density at which salt begins 

 to deposit, as observed at the ponds and confirmed by laboratory experiments, is 

 1.2121, and that of the escaping mother liquors is 1.2345. The yield of salt is at the 

 rate of 150 tons per inch depth per acre. The crop is gathered on horse cars, which 

 run on movable tracks into the ponds. At the works the operations are simple and 

 effective. A link-belt conveyor carries the coarse salt to the crusher; thence to the 

 dryer, after which a sifting process is employed by which the salt is separated into 

 table salt and dairy salt. 1 [See Specimens Nos. 53630-53634, U.S.N.M.] 



Owing to the depth below the surface of the salt beds in Ohio, 

 Michigan, and other inland States, the material is never mined as in 

 the cases first mentioned, but is pumped to the surface as a brine and 

 there evaporated by artificial heat. In the Warsaw Valley region 

 the beds lie from 800 to 2,500 feet below the surface, and are reached 

 by wells. These are bored from 5 to 8 inches in diameter and are 

 cased with iron pipes down to the salt. Inside the first pipe is then 

 introduced a second, 2 inches in diameter, with perforations for a few 

 feet at its lower end, and which extends nearly if not quite to the bot- 

 tom. Fresh water is then allowed to run from the surface down 

 between the two pipes. This dissolves the salt, and forms a strong 

 brine which, being heavier, sinks to the bottom of the well and is 

 pumped up through the smaller or inner tube. At S} 7 racuse the wells 

 are not sunk into the salt bed itself, but into an ancient gravel deposit 

 which is saturated with the brine. Here the introduction of water 

 from the surface is done away with. In those cases, not at all 

 uncommon, where the brine flows naturally to the surface in the form 

 of a spring, pumping is of course dispensed with. 



The methods of evaporation vary somewhat in detail. In New 



1 Science, XIV, 1889, p. 445. 

 NAT MUS 99 14 



