1892.] 



DAFERT AND DERBY SEPARATION OF MINERALS. 



125, 



hope of a solution was to be found in the principle of a moving col- 

 umn of liquid, long employed for an essentially different purpose in, 

 agricultural chemical laboratories. A very neat little apparatus for 

 this purpose has already been devised by M. Thoulet (Fouque et 

 Levy, Mine'ralogie Micrographique^ p. 120) but it does not appear to have 

 come into general use. The essential defects of the method have 

 been indicated by Prof. Rosenbusch [i\Iik. Fhys. 188^, /., /. 206) as- 

 follows : " The separation of a mixture of different minerals of equal 

 grain through the mechanical effect of a stream of water is not 

 obtainable with any degree of exactness ; the division takes place 

 principally according to size and form of the grains, so that flakes 

 are moved more readily than grains, and not according to the specific 

 gravity, even when this is very different among the components of 

 the mixture." This condemnation of the principle is, however, too 

 absolute as will be seen by the results obtained by the apparatus 

 described below. Once that the idea of complete separation, impossible 

 to obtain above sp. gr. 3.6, is abandoned, and we content ourselves 

 with a more or less satisfactory concentration, the principle objections 

 to the process disappear and, with the improvements of which it is 

 susceptible, it becomes a valuable aid in the laboratory. 



/. Description of the Apparatus. * 



Starting on the basis of the Thoulet appar- 

 atus, we have modfied the separator (fig. 2) 

 in such a way as to permit the withdrawal of 

 the lighter material in a perfectly regular man- 

 ner without disturbing the operation (thus inci- 

 dentally making the apparatus continuous in its 

 action) and to do away with secondary cur- 

 rents within the tube. To this, we have added 

 the accessories (figs, i, 3 and 5) for securing, 

 automatically, regularity in the current. 



The pressure regulator (fig. i) may be 

 made from a simple Wolff flask and should be- 

 placed at about two meters, at most, above the 

 work table. The dimensions of the single 

 parts are : cubic contents of flask, 2 liters ; 

 FiG.i diameter of tube a, 3 mm.; of tube b, 10 mm.;, 



of tube r, 3 mm. 



inrtf 



* The apparatus here described can be obtained from C. Gerhardt, Marquarte Lager, Bonn. 



