THE USE OF THE -ELECTROMAGNEFT 1 
PETROGRAPHY 
By T. CROOK, A-R.C.Sc.1., F-G.S. 
Scientific and Technical Department, Imperial Institute 
1. INTRODUCTION : : . - . . ; : . 3» 
2. HISTORICAL REVIEW . : 2 : ; : : : ot 
3. APPARATUS REQUIRED. : : : : . : é . 43 
4. PREPARATION OF MATERIAL : 5 E , : : - 46 
5. SEPARATION OF THE MINERALS. - - . - : . 46 
6. CONCLUSION . : : . ‘ 3 : ? : ; ; 50 
1. INTRODUCTION 
Ir is well known that minerals exhibit varying degrees of 
permeability in a magnetic field, in consequence of which 
grains of one mineral can often be separated from those of 
others. In recent years the method of magnetic separation 
has become very important in the mining world. It is quite 
indispensable in a large number of ore-dressing operations, 
in which domain its utility is fully recognised. 
In the laboratory also, this method has often been used with 
great advantage, more especially in the isolation of minerals 
for chemical analysis. Indeed, the magnet, and especially the 
electromagnet, must be regarded as a very useful piece of 
petrographical apparatus. Experience has shown that it is 
capable of extensive use qualitatively, while in special cases 
it yields quantitative results which are fairly accurate, particu- 
larly in the examination of sands. 
Considering the ready and extensive applicability of this 
method in rock studies, there is scope for surprise that it has 
not been more widely adopted, for there can be little doubt 
that, among geologists, the practical utility of the method is 
much undervalued where not completely ignored. This may 
be due in some measure to unfamiliarity with the results already 
achieved. Hence it is proposed in this article to give an 
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