146 GEOLOGY OF OHIO. 



This arrangement, which cost not over $50.00 and required not over 

 one-fourth horse power, screened two hundred tons in a day with no 

 attention but an occasional sweeping by a boy. 



2nd. The same general style, but narrower, suspended by flat steel 

 spring bars and driven by eccentric. This screen invariably gave trouble 

 until the method of suspension was changed to round rods, instead of 

 flat springs, which speedily crystallized and broke. The eccentric also 

 uses more power, and wears out faster and is more expensive to repair 

 than the simplest crank. 



3rd. A screen box, about thirty inches to ten feet long, pivoted at 

 the lower end and shaken from side to side at the upper end by a rapid 

 crank motion; this inclination about three feet in ten. 



This is, all things considered, the best shaking screen in use — it is 

 cheap — simple — and requires less power to run it than any other, and it 

 will do more work per square foot of surface. The motion of the 

 screen from side to side is quicker, but less violent than the longer sweep 

 from end to end of the first shaking screen described. The jar of the 

 latter is hard on a weak building. 



The general results obtained, indicate that where a high building is 

 to be used, the incline screens are the best as by duplication the capacity 

 can be brought up to any demand. Where a low building is to be used 

 and the quantity of work is large, the shaking screens will be found the 

 best and of the shaking screens, those which accomplish the main move- 

 ment of the clay down the screens, largely by gravity and the short lat- 

 eral motion, back and forth, by power. ; 



The fineness to which it is advisable to reduce the clay for making a 

 vitrified ware varies with the qualities of the clay. If the clay is refrac- 

 tory, it should be ground fine; if it is easily vitrified it need not be made 

 so fine. 



If it is plastic it may be left coarse, if it is rough it must be made 

 fine. The effect of fineness of division in the clay in the character of 

 the ware is noticeable; it increases the danger of bloating, and increases 

 the danger of bad structure by too great plasticity, but the results are 

 firmer and stronger knit. For paving material it is beneficial in increas- 

 ing the wearing qualities, and in sewer pipe it assists in getting an even 

 smooth surface. 



The clay from the screens is allowed to fall into a storage bin if the 

 tempering processes are to be done by a wet pan, or go direct to the pug 

 mill if the tempering is to be done in that machine. The use of a stor- 

 age bin for tempering by pug mill is very rare, but it has many advant- 

 ages to recommend it. 



The tempering of clays for the use in the finishing machinery, is one 

 of the most important steps in the process. Mismanagement in grinding 

 and screening results in lost time; mismanagement of tempering affects 

 the value of the ware produced. 



