1s ROYAL SOCIETY OF CANADA 
described apparatus used by them for the purpose in the Proceedings of 
the Rochester Academy of Sciences. (Vol. ï1., p. 122.) 
Dense liquids are being more and more employed in the separation of 
minerals from mixed aggregates. Their use, of course, depends upon their 
being deriser than some of the minerals in the aggregate and lighter than 
others, the heavy minerals sinking to the bottom of the liquid, and the 
light ones floating. By gradually diminishing the density of the liquid a 
series of separations can often be made. Obviously the liquid must be 
one which has no chemical action upon the minerals concerned. It should 
also be as mobile as possible if the particles are to settle readily, and 
should be easily recovered so as to be used again. 
Among the dense liquids which have been employed is Thoulet’s 
solution, an aqueous solution of potassium-mercuric iodide, whose maxi- 
mum density is 3196; Klein’s solution (cadmium borotungstate) as 
ordinarily employed has a density of about 3:36, and, like Thoulet’s, is 
miscible with water in all proportions, so that its density may be reduced 
to any desired point and the water afterwards removed by evaporation. 
Rohrbach’s solution (barium-mercuric iodide) has a higher density (3:588) 
than the two last named, but has the serious disadvantage of undergoing 
decomposition on dilution with water. Methylene di-iodide” has proved 
useful in some cases. Its specific gravity at 16° C. is 3°3243, and this can 
be diminished by addition of benzole, but not of water or alcohol, The 
benzole can afterwards be removed by evaporation. 
Certain salts in a fused condition have proved very satisfactory and 
have a much higher density than the liquids already described. Silver 
nitrate,’ for example, fuses at about 198° C. to a clear mobile liquid of 
about 4:1 sp. gr., and the density can be diminished at will by the addition 
of potassium nitrate. The operation may be performed in a test-tube, 
which, along with a thermometer, is suspended in a small beaker by means 
of an asbestus card. The small beaker is in turn suspended in a larger 
beaker by means of another asbestus card and the whole heated on a sand 
tray or iron plate. On cooling the salts solidify to a mass with the lighter 
and heavier minerals at the top and bottom respectively. The test-tube 
is broken away from the fusion, the parts of the latter containing the 
minerals cut or broken off and the nitrates removed by solution in water. 
Of course, here, as in other cases, it is necessary that the salts should not 
act upon the minerals and that the latter should not suffer decomposition 
on account of the temperature at which the experiment is performed 
(225°-250° C.). This method, I may remark, has in some cases given me 
excellent results. 
Where available the double nitrate of thallium and silver (also sug- 
' Suggested by R. Brauns, Jahr. f. Min, 1886, ii., 72. 
2Suggested by Dr. J. W. Retgers, Jahrb. f. Min, 1889, ii., p. 190. 
