'■■] 



DAFERT AND DERBY SEPARATION OF MINERALS. 



125; 



d 



The dimensions of the apparatus with which experiments have- 

 been made are : fig. 3, diameter of tube and cocks, 4 mm.; fig. 2, 

 diamter of a, 4 mm., / 10 mm., ^, 7 mm., d, 3 mm.; height of/, 140 

 mm., g, 330 mm , ^, 520 mm., to /, 280 mm. 



The technical points that were kept steadily in 

 view in devising the apparatus are the following : 

 I. — Water is preferable to all other liquids for- 

 the purpose of separation. 



2. — One must not only be able to sharply regu- 

 late the velocity of the current, but also to re-estab- 

 lish it at any given time with approximate accuracy. 

 3. — In any given sand the separation according; 

 to specific gravity is only possible when, 



(a.) — The mixture to be separated is as far as pos- 

 sible of equal grain, in which is included not only^ 

 equality as regards volume, but also, so far as possi- 

 ble, similarity of form as well. 



{i>.) — When the substance to be separated never- 

 can leave the liquid column, settle in some point out- 

 side of it, come irregularly into motion and then 

 remain at rest, etc. 



(c.) — When in the moving column of liquid the- 

 current is as uniform as possible, and, especially, 

 moving in all parts in the same direction. 



((/.) — When the apparatus in no place affords an 

 opportunity for the formation of "false currents," as. 

 for example, at the joints which may form eddies in 

 the current and thus impede a regular separation. 

 riG.'i. (>.) — When after the arrangement in the current, 



of the mineral elements according to specific gravity, the withdrawal; 

 is effected without disturbance of the pressure or of the direction of 

 the current in the fluid column. 



(/.) — When the current is as weak as practicable, and finally 

 {g.) — When the operation of separation can be repeated as often- 

 as may be desirable. 



Numerous experiments with different forms of apparatus and 

 under various conditions for the purpose of determining how far- 

 these theoretically desirable points are attainable in practice, lead to- 

 the following conclusions : 



I. — A priori, it would appear that the denser the liquid. 



