30 SYDNEY H. BALL: 
of the chalcopyrite and the silver value of the galena being eventually 
recovered. 
No milling, as stated above, is done at the mine but the process 
at Øresund, Denmark is as follows: 
The crude cryolite is broken up by hammers (Fig. 15) to pieces 
approximately 50 mm (2 inches) in diameter and this is then screened 
and the impurities removed from the larger pieces by a power chisel 
resulting in а commercial product. The fines and the rejects are then 
crushed and submitted to an air blast which removes dust and any 
particles of wood included. This is then sized into three products; the 
first over 14 mm (0.5 inches), the second from 1 to 14mm (0.04—0.5 
inches) and a third under 1 mm (0.04 inches). The coarse is then con- 
centrated, next crushed and again screened. The fines are first washed, 
then classified and lastly buddled. The above treatment of the fines 
results in two products, one practically pure cryolite and the second 
the associated minerals with approximately 10 % of cryolite. Both 
products are then dried whence they pass to electro-magnetic separaters 
in which the cryolite 1$ treated once. The impurities are re-treated in 
the separators and then jigged, chalcopyrite, siderite, sphalerite and 
galena products being formed. The residual сгуоЩе is carefully ground, 
the included quartz remaining in larger particles then being separated 
from the cryolite by screening. 
The ground cryolite is a practically pure product being free of 
lead, copper and zinc and containing not over 0.12 % of iron. 
Up to a short time ago the most important use of cryolite was 
for making soda, the process both at Natrona, Pa., and at Огезапа, 
Denmark being practically identical. The cryolite is first finely ground, 
and after being mixed with lime is heated in reverberatory furnaces 
to redness, the mixture being frequently stirred. The cryolite breaks 
down into aluminate of sodium and fluoride of calcium. The charge, 
known as “cryolite ash’’, is withdrawn from the furnace and is leached 
with hot water in iron vats. The calcium fluoride is insoluble and 
the aluminate of soda, together with any sodium carbonate or caustic 
soda, which may have been formed, goes into solution. The concen- 
trated solution is next treated with carbonic acid, resulting in the 
formation of sodium carbonate and aluminum hydrate. 
The sodium carbonate solution is then drained off the aluminium 
hydrate into evaporating pans of about 50 tons capacity. Here it is 
concentrated and is then drawn off into tanks where the sodium car- 
1) See particularly Holland: Jr. of Ind. & Eng. Chem. Feb. 1911, pp. 65—6 
and Uber Gewinnung und Bedeutung des natürlichen grönländischen Kryolithes. 
Dr. JuLıus GRUNWALD. Coburg 1914. 
