78 
Journal of the Mitchell Society 
[ November 
it. The sand brought into the magnetic concentration plants is 
worth from 4 to 8 cents per pound while after a magnetic separa- 
tion, its value is increased to 12 to 20 cents per pound. 
This material represents what is known as crude monazite sand 
and contains, besides the monazite, magnetite, ilmenite, garnet, 
zircon, rutile, corundum, cyanite, hornblende, and occasionally 
chromite. In order to separate the monazite from its associated 
minerals, it is necessary to run this crude sand through some elec- 
trical apparatus. There are two types of machines that are in 
operation : (1) the Wetherill electro-magnetic machine and modi- 
fications of this; and (2) machines in which the minerals are 
deflected by electro -magnets while falling. Of these, the first type 
is the one most generally employed. By means of these various 
machines a product can be obtained varying from 90 to 98 per 
cent of monazite and represents the sand that is shipped to the 
manufacturers of the incandescent mantles. 
MAGNETIC SEPARATION 
The first application of magnetic separation was in the concen- 
tration of certain iron ores, principally magnetite, in order to pro- 
duce a product richer in iron and also to eliminate certain miner- 
als that contained elements injurious to the metallic iron. The 
next application was to other iron ores such as limonite, hematite, 
and siderite after they had been given a preliminary roasting to 
convert them into the magnetic oxide. The next step was in the 
separation of magnetic iron particles from certain copper, gold 
and zinc ores either before or after roasting. For many years this 
was the only application made of magnetic separation. It was 
found, however, upon experimenting with an electro-magnet with 
a higher intensity that other minerals were subject to magnetic 
attraction and that it was possible to separate minerals into more 
or less pure products by varying the intensity of the magnetic 
field. Thus, it has been possible to adapt this method of separa- 
tion to ores containing iron or manganese, which are only weakly 
magnetic. As is well known, steel bars may be magnetized and 
they will retain more or less of this magnetism indefinitely, while 
bars of softer wrought or cast iron may be magnetized by means 
of electric currents in surrounding coils of insulated copper wire. 
