446 S. L. Penfield—Devices for the Separation of 
Art. XLIX.—On some Devices for the Separation of Min- 
erals of high specific gravity ; by 8. L. PENFIELD. 
MINERALOGISTS and _petrographers are certainly greatly 
indebted to Dr. J. W. Retgers* for the fortunate discovery 
that the nitrates of silver and thallium, when mixed in the 
proportion AgNO,: TINO,=1:1, yield a double salt which 
fuses at about 75° C. to a clear mobile liquid, having a specific 
gravity of over 4°5 and capable, while melted, of being mixed 
with water in all proportions. The material is easily prepared 
by dissolving a weighed quantity of thallium im nitric acid, 
evaporating on the water bath until the excess of acid is 
expelled and then adding sufficient silver nitrate to make a 
double salt of the composition given above (8°33 gers. AgNO, 
to every 10 grs. of thallium). The salt is readily soluble in 
warm water and may be reclaimed by filtering the solution 
and evaporating it on the water bath to its maximum concen- 
tration,. care being taken as far as possible to avoid dust and 
impurities. 
As recommended by Retgers, the operation may be per- 
formed in a test tube heated in a water bath, and after the 
separation is completed the fusion is allowed to cool, when the 
salt solidifies with the heavier mineral grains at the bottom 
and the lighter ones on top. On breaking the test tube and 
dividing the mass the separated minerals may be obtained by 
dissolving in water. The operation cannot well be performed 
in the ordinary glass stop-cock separating funnel, and there are 
disadvantages in using test tubes, because, if in an operation 
one desires for any purpose to obtain the heavy material which 
may have separated out, one must interrupt the whole process, 
while again if considerable water has been added and one is 
. working with the liquid when the specific gravity ranges from 
3 to 4 the fusion or solution does not yield, on cooling, a solid 
cake, but a mass of wet crystals, which it is rather unpleasant 
to manipulate. 
A simple glass stop-cock device, by means of which succes- 
sive portions of the heavy material can be drawn off from the 
bottom, has been described by D. A. Kreider and the author,t 
~ but a still better apparatus can now be recommended. The 
idea is not an original one, but was suggested by an apparatus 
devised by Contollence and exhibited to the author by Prof. 
I’. Fouqué at the Collége de France, Paris. As modified for 
use with the Retgers double salt it is shown in section, about 
* Jahrb. f. Min., 1893, i, p. 90. 
+ This Journal, ITJ, xlviii, p. 143, 1894. 
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