80 Journal of the Mitchell Society [November 
onite 72 to 43. By using the electromagnetic separators, which 
can be regulated so as to give a very strong field and at the same 
time a field which is capable of fine adjustment, it is now possible 
not only to separate the paramagnetic from the diamagnetic sub- 
stances, but also to separate the paramagnetic from each other. 
There are a large number of magnetic separators that have been 
invented, many of which are now on the market. Perhaps the 
simplest of all these magnetic separators is one devised by Edison. 
In this separator the particles of mineral are permitted to fall in a 
thin sheet in front of the poles of a strong bar electromagnet, which 
causes a deflection of the magnetic particles from a direct down- 
ward path, while the nonmagnetic particles would not be 
influenced by this attraction and would fall vertically. It is possi- 
ble to make two and sometimes three products in this way. 
There are three general classes of these magnetic separators as 
follows: (1) in which the magnetic particles are held to revolving 
cylindrical rolls or drums within which are magnets; (2) those 
in which the magnetic particles are carried by conveying belts or 
pans passing over the magnets; (3) those in which the ore falls in 
front of a magnet. There are a number of points of difference in 
the machines such as permanent or electromagnets; treating the 
ore wet or dry ; magnets acting continuously or intermittently ; 
and the use of direct or alternating current. It will be found that 
different machines are suited for different purposes according to the 
character of the material to be treated. As I have stated before, 
most of the machines were originally designed simply to treat iron 
ores, or to separate iron minerals from other ores and there are 
but few of them that are adapted for the separation of monazite, 
zinc minerals, etc. 
The first class is represented by the Ball-Norton separator which 
consists of two revolving drums within each of which is a series of 
stationary electro-magnets so wound that opposite poles are adja- 
cent to one another. The capacity of a machine with 2 drums 2’ 
dia. and 2' face raises 15-20 tons per hour, 16-20 mesh. The ore 
is fed upon the top of the first drum and the magnetic particles 
are held by the drum, while the non -magnetic fall into the hopper 
below. As the drum revolves, the magnetic particles get beyond 
