1892.] DAFERT AND DERBY— SEPARATION OF MINERALS. 1 27 



working in a circular socket" instead of the usual circular opening. 

 The wax that the glassblowers are so fond of putting in their cocks 

 must be carefully removed before using, as its presence makes the 

 regulation of the flow impossible. 



3. — The condition a cannot be completely satisfied. A close 

 approximation to regularity of grain may however be obtained by 

 the use of fine sieves (bolting cloth makes the best) and by repeating 

 the separation in water with a strong current and a higher column of 

 sand. It must be confessed, however, that this is the weak point 

 of the apparatus and that we have only partially succeeded in remov- 

 ing the difficulties of a difference in the size and form of the mineral 

 grains. If a solution of this problem were practicable, it is evident 

 that the method would be the most complete imaginable. This, how- 

 ever, is impossible and in practice we have found that with careful 

 work, the difficulty can be so far overcome that, notwithstanding this 

 ■defficiency, the method is very useful. 



The conditions I' — e are almost completely satisfied in the appara- 

 tus above described, as a simple inspection will show, whereas in all 

 the previously devised separators that have come to our knowledge a 

 regular separation is excluded by the very form of the apparatus. 



In observing the motion of the particles in any ordinary separa- 

 ting apparatus, it will be seen that even in the narrowest tube, grains 

 of equal size and specific gravity show by sinking, the existence of a 

 counter current that renders impossible a separation according to 

 specific gravity. This difficulty may be overcome in three ways : 



[a) — By provoking a circular motion in all the mineral mass 

 floating in the liquid column, by twirling the apparatus. 



(/?) — By producing a spirally flowing water column which will 

 force back into the current at another point, every mineral particle 

 that gets out of the current. 



(f) — By the introduction in the current of a spiral which diverts 

 the counter currents and throws them again into the proper upward 

 flowing stream. 



All three of these are technically practicable. They also appear 

 to be of equal efficiency when certain conditions are satisfied. We 

 have chosen principle c as being the simplest to arrange in the appara- 

 tus. An experiment with and without the spiral will show a marked 

 dift'erence in the practicability of the process of water separation. 

 We should remark that the spiral should neither rest on the inner nor 

 the outer tube, and therefore the diameter of the coils should be 



