122 ROCHESTER ACADEMY OF SCIENCE. [April l8. 



The following paper having been accepted for publication by the 

 Council was read by title : 



ON THE SEPARATION OF MINERALS OF HIGH 

 SPECIFIC GRAVITY. 



P.v E. W. Dafert, M. a., Ph. D. and O. A. Derby, F. G. S. 



{Communicated from the laboratory of the Cotnmissao Gcograph- 

 ica e Geologica de Sao Paulo, Brazil. 



The various processes that have been devised during the past 

 few years for the separation of fine grained mineral mixtures by 

 means of heavy liquids, the electro magnet, etc., have greatly extended 

 the field of mineralogical and petrographical research and are of 

 almost daily application in the laboratory. By their use, the rarest 

 accessory elements maybe quickly and readily isolated from the super- 

 abundant essential elements and, within certain limits, separated from 

 each other, for the purposes of study and identification. The appli- 

 cation of the batea described by one of us in a recent number of this 

 journal, renders practicable the obtaining of sufficient quantities for 

 analysis of these rare and fine grained minerals, and thus their sepa- 

 ration in a state of purity becomes a matter of great importance. 



The limit of complete separation by means of heavy liquids is at 

 present fixed at sp. gr. 3.60-3.65, obtained by Retgers {Neues Jahr- 

 buch, iS8q, II. p. 188) by saturating methyline iodide with iodoform 

 and iodine. This limit has been extended to sp. gr. 5 by Breon and 

 Retgers, by the use of fused zinc, tin and silver salts, but these pro- 

 cesses have, in our hands at least, proved very tedious and unsatis- 

 factory. Under the most favorable hypothesis, the process by fusion 

 does not dispense with the subsequent sorting under the lens, since 

 the operator cannot follow the separation closely with the eye and the 

 division of the cooled ingot at the proper point is a matter of 

 chance. 



The separation by the electro-magnet is limited by the magnetic 

 properties of the minerals and, even when applicable, is seldom so- 

 complete as to dispense with the use of the lens. In general, there- 

 fore, it may be said that above sp. gr. 3.6 and with minerals that do 

 not vary greatly in magnetic properties, the most that can be obtained 

 is a concentration of the different minerals in different portions, that 

 greatly facilitates the process of sorting. 



In seeking a process of general applicability that would at least 

 give a satisfactory concentration, it has seemed to us that the best 



