98 



DRESSING OF ORES 



revolving in tho trough D. Tho heads are solid cylinders of iron attached to wrought- 

 iron lifters, and when in work are rotated by the action of the long cams F. Tho lift 



or rise of the head is varied by tho blocks E E, which traverse a flat thread screw cut 

 in tho lifter. It will be seen that no stuff can bo lost through the bottom of the coffer ; 

 whilst an economic advantage is secured by the use of a largo area of perforated plate 

 or grate. At a speed of 70 to 80 drops per minute one cwt. of stuff, is reduced to 

 millimeter size per hour, the quantity of water per head being about 4 gallons per 

 minute. 



German Stamping Mills. To the German miners we are indebted for tho general 

 arrangement of the Stamping Mill. In a work, ' De Eo Motallica,' by Agricola, edition 

 1621, many different mills are illustrated, showing clearly that all tho essential 

 features of the modern mill were then well known. In Rittinger's ' Lehrbuch dor 

 Aufbereitungskunde,' and other important works on Dressing, tho subject of stamping 

 mills is, generally, well and profoundly treated, and rendered clear by tho aid of 

 numerous illustrations. The following particulars of a practical character will, how- 

 ever, bo interesting : 



Stamp Head. Average weight, 300 Ibs. 



Minimum 100 Ibs. ; maximum weight, 500 Ibs. 



Fall of Head. Average 8 inches. 



Maximum, 12 inches, for coarse stamping. 



Minimum, 4 inches, for fine stamping. 



Wear of Head. Made of grey iron, after stamping 5 tons of stuff to a size of 1 



millimeter. 



Hard tough stuff . . . . 11 to 13 Ibs. 



Middling hard stuff . . . . 8 10 



Moderately . . . . 5 7 



Wear of Anvil or 'bottom' of wist iron 4 inches thick, per 5 tons of stamped stuff. 

 Hard tough stuff . . . . 4 to 5 Ibs. 



Middling . . . . 3 4 



Moderately . . . . 1 2 



