20 BULLETIN 572, U..S. DEPARTMENT. OF AGRICULTURE. 
entering the treaters are cooled by radiation in the flues to the 
desired temperature for the precipitation of the dust. 7 
Several precipitating installations are also in operation at plants con- 
trolled by the Universal Portland Cement Co., but as indicated in Table 
I the dust from these plants is too low grade to be of value as a source 
of potash. The dust collected in the treaters at these plants, there- 
fore, is returned to the kilns automatically, for use as cement material. 
In the precipitating system recently installed at the Cementon 
plant of the Alpha Portland Cement Co., the gases from the kilns 
are passed successively through a boiler and economizer system 
before entering the treaters. In this way the waste heat of the gases 
is utilized for the generation of power by steam turbines. In this 
installation, as well as in the multiple-pipe treaters already referred 
to, an artificial draft produced by a fan placed beyond the treater 
system replaces the natural draft originally given by the flue stacks. 
The advantages claimed for installations of the kind last mentioned 
are as follows: (1) The abatement of the dust nuisance is effect- 
ively secured; (2) material is recovered suitable as a source of 
potash or cement material or of both when separation of the potash 
is brought about; (3) a greater efficiency in the burning of the cement 
is secured owing to better possible regulation of the draft through 
the kilns, with resultant.economy in the amount of fuel required; and 
(4) utilization of the waste heat of the gases from the kilns. 
In the plant of the California Portland Cement Co. use is made of 
the Fleming patent dust-collecting system. This system has been 
in operation since 1912, and it is claimed that this method of collecting 
the dust is not only efficient but it is also more than self-supporting, 
there being a saving to the company in the dust collected, a larger 
output per barrel of oil used for fuel, and fewer shutdowns than before 
the Fleming system was installed. 
The draft for the kilns is produced by fans sucking at the end of 
separate flues. Instead of discharging the gases into the atmosphere, 
these fans blow the dust. and pies into a large dry dust-settling 
chamber, where the velocity of the gases is reduced 90 to 95 per cent 
and about two-thirds of the dust is deposited. The gases carrying 
the extremely fine dust which does not settle then go to wet washing 
chambers, where they are forced up and down several times through 
a system of seven baffle sections in each of which are sprays of water 
for capturing the remaining dust. In both the wet and dry chambers 
means are provided for removing the collected dust to the cement 
kilns. The same water being repeatedly used in the wet baffle cham- 
bers, itsoon becomes charged with soluble salts, principally in the form 
of sulphur compounds of potassium, sodium, and calcium. When 
more than one-half pound per cubic foot is found some of the solution 
is removed. and replaced by fresh water in order not to cause trouble 
1 Hanna, W. C., Metallurgical and Chemical Engineering 13, 609 (1915). 
