Kies— Physical Tests of Devonian Shales. 



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efficient and economical. The economy of this latter method depends, how - 

 ever, on its being kept at work as steadily as possible, and consequently it is 

 chiefly applicable to larger plants. 



Preparation. Before being mixed with water or tempered, the shale is 

 first ground in dry-pans or disintegrators. 



Dry-pan. This consists of a circular iron pan with perforated bottom. 

 In the pan are two mullers about twelve inches wide and supported on a 

 horizontal axle. The mullers weigh from 2,000 to 4,000 pounds and revolve by 

 the tangential friction of the pan floor, which is turned by power transmitted 

 from the engine. Scrapers attached to the axle of the mullers keep the mate- 

 rial charged, in their path. The shale when ground fine enough falls through 

 the slits in the pan-bottom. These slits are generally one-eighth to three- 

 sixteenths of an inch wide. The capacity of a dry-pan varies with the size 

 of the screen openings and character of the clay, but one hundred tons in ten 

 hours with one-eighth inch screen openings is a fair capacity. 



Disintegrators, consisting of concentric wheels bearing cross pieces and 

 revolving in opposite directions, or of an axle bearing steel arms which revolve 

 between a series of parallel steel bars, are often found effective. The pieces 

 of shale are ground not only by being hit by the rapidly moving arms, but 

 also by being thrown against each other. 



Screening. The ground shale is generally transported from the dry-pans 

 or disintegrators to the screens by means of bucket elevators or traveling 

 belts. Three general types of screen are used. 



1. Inclined screens, ten to fourteen feet long, with wire cloth or perforated 

 metal bottom. They are often provided with a tapping device to keep them 

 from becoming clogged. Inclined screens are simple and cheap, but have 

 small capacity. 



2. Rotary screens, of cylindrical or octagonal form, usually provided with 

 automatic devices, such as brushes to keep them clean. 



3. Shaking screens, fixed at one end and driven by crank and piston or 

 eccentric. These are cheap and simple in operation. 



While all these screens are designed to perform their work automatically, 

 still few of them can be left without attention for any length of time. 



The tailings from the screens are returned to the crusher or disintegrator. 

 Tempering is usually done in wet-pans or pug-mills. 



Wet-pans. These resemble dry-pans, but have a solid instead of perfo- 

 rated bottom. The clay is charged in lots of 600 to 1,000 pounds and water 

 added. Wet-pans are very rapid in their action, a charge for brick or sewer 



