42 The N.Z. Journal of Science and Technology. [Jan. 
pulps and one being placed between each cell. The centrifugal pumps are 
peculiar in their construction, consisting of a disk runner with lugs on the 
sides operating between rows of similar lugs attached to the pump-shell. 
The object of the lugs is to break up the lumpy tailings. Tapped into the 
suction-inlet of the pump is a pipe which is branched a few inches above the 
point of union with the suction, the second branch leading to a sulphur- 
burner. The sulphur-fume is drawn in along with air which enters in the 
main branch of this pipe, the mixed gases being thus carried into the pump 
entrained in the pulp-feed. The pulp is delivered to the pump from an 
agitator-tank, which in turn is supplied from a tailing belt conveyer, upon 
which is fed salt cake in the proportion of from 2 lb. to 2J- lb. per ton of 
tailing. The charge in the agitator is heated to 90° C. before being drawn 
to the centrifugal pump, and is then forced through cell No. 1, from which 
a lead-froth concentrate is delivered. The tailing from this cell passes 
through a second pump, also drawing in air and S0 2 , but no more S0 2 is 
added beyond this point. By the time the solution has reached cell No. 5 
all the SO 2 has been evolved from the pulp, and zinc concentrate begins 
to appear with lead in the froth. The mixed concentrate from cell No. 5 
is returned to the agitator, and once more traverses the first series of 
flotation cells. The tailing from No. 5 cell is heated to 120° C. by steam, 
and about 18 lb. of H 2 S0 4 per ton of pulp solids is added. This pulp is 
then circulated in the same manner as before, through five cells, producing 
a zinc concentrate. The success of the process is due to intense aeration 
in combination with the effect of S0 2 retarding the flotation of the zinc 
sulphide until the lead has been lifted. 
Another process for preferential flotation has been adopted by the 
sulphide corporation in the use of the Seal-Shellshear machine. The jet 
from the feed-boxes produces an exhaust, drawing air downwards into the 
delivery column below the perforated cast-iron jacket; the stream, under 
pressure due to the head, strikes the baffle, which produces by reaction 
sufficient agitation with the entrained air to develop froth that lifts the 
galena. A small quantity of eucalyptus oil is added to the pulp as a 
flotative agent. These cells are connected in series, and the tailing from 
cell No. 5 goes to a Hebbard machine, where the pulp is heated to 120° C. 
by a steam-jet; and H 2 S0 4 and eucalyptus oil are added, thus effecting 
the flotation of the zinc-blende. 
To render carbonates and oxides amenable to the flotation process it 
is necessary to give a preliminary sulphidizing treatment. This is done 
by treating the ore with (1) hydrogen sulphide, (2) solutions of sulphides 
and sulpho-compounds of sodium and calcium, (3) sulphur vapour. The 
object of this preliminary treatment is to cover the carbonates and oxides 
with a thin layer of sulphide, after which their treatment is the same as 
natural sulphides. 
Oils. 
The proper kind of oil to use can only be determined by experiment, 
for what is suitable for one class of ore may be altogether unsuited to 
another. As a general rule lubricating oils are of little value, and have 
been replaced in flotation-works by oils more or less soluble in water. The 
very volatile oils—such as naphtha and gasoline—are of little value, except 
perhaps to make the pitchy ingredients of coal-tars more soluble. Wood 
oils and oils derived from the distillation of wood oils are good brothers, 
while coal-tar oils are good collectors. In Australia crude eucalyptus oil is 
used with good results, while in America pine oils as well as mixtures of 
pine oils and coal-tar oils are used. 
