CRUSHING AND PULVERIZING MACHINERY. 459 



longitudinal section, if taken when the mill is at rest, would show the 

 material in the shape of an acute-Tingled triangle, with point at delivery 

 end and base at the inlet; the transverse section at the inlet will, there- 

 fore, show a large amount of material to a small amount of flint balls, 

 and a transverse section at outlet end would show the mill half full of 

 flint balls, with but a small amount of material extremely finely ground. 

 Between these two points there is a progressive disposition of the balls 

 and material, but at the same time the flint balls are evenly distributed 

 throughout the tube. Applying the principle enunciated above it will 

 be seen that the coarse grinding is accomplished where the proportion 

 of material is great in relation to the flint balls, and that the mere fact 

 of delivery at the periphery of the other end compels an automatic 

 and gradual adjustment of relations between balls and materials, so that 

 at the delivery end a transverse section would show the mill half filled 

 with balls with but a small portion of material subject to the grinding 

 action. 



" The speed at which the tube revolves tends to carry the mixture of 

 balls and material to a certain height in the mill from which point balls 

 and material fall together rolling and grinding as they seek the bottom 

 of the mill; the action might be likened to the action of water at the 

 crest of a wave. This sort of action can only take place when the mill 

 has been half filled with the flint balls; if less than a proper charge of 

 flint balls is used the whole mass has an inclination to only slide upon 

 the inner surface of the tube, and none of the turbulent wave-crest 

 action suggested takes place. Of course, much the best grinding is 

 accomplished through keeping the whole mass of material grinding and 

 pounding. 



"The tube is lined with iron, specially made tiles, or a natural stone 

 which we have named 'Silex.' These are set with Diamond cement 

 made only for this purpose. Any bricklayer can readily lay up a lining. 



"The life of a lining depends upon the character of the materials 

 ground on it. With ordinary care all linings should last at least a 

 year. In most cases linings have served eighteen and twenty-four 

 months. Experience with Silex indicates that it will serve two or 

 three years of continuous grinding. 



"Experiment has proven that for grinding, flint balls are positively 

 the most economical medium. The tube mill has therefore been de- 

 signed for and proportioned for the use of flint balls. 



"The tube mill for grinding slurry or wet materials is designed to 

 use steel balls instead of flints, and is proportionately heavier in con- 

 struction. 



