16 BULLETIN 1226, U. S. DEPARTMENT OF AGRICULTURE. 
in the stoves and boilers of different plants. The average given by 
W} 7 sor for dusts collected at the Bethlehem plant amounted to 9.9 
per cent. The average value which we have found for the potash in 
78 samples of dust collected at various other plants amounts to only 
2.9 per cent, or less than one-third of that for the Bethlehem plant. 
If our value of 4.9 pounds be taken as to the average quantit} - of 
potash volatilized per ton of pig iron and an average normal pro- 
duction of iron of 33,700,000 gross tons be assumed, then the total 
potash volatilized from the blast furnaces of this country will amount 
to about 84,000 tons, as compared with the 87,000 tons found for 
cement plants. As there are twice as many blast-furnace plants as 
cement plants in the United States, the quantity of potash lost per 
individual plant must therefore be less in the blast-furnace industry 
than in the cement industry. 
POSSIBILITY OF POTASH RECOVERY. 
When the survey was made of the cement industry it was recog- 
nized that the dust from some plants was probably too low grade 
ever to be used as a source of potash, even if no cost were involved 
in collecting the dust. The richness of the dust in other plants 
indicated, on the other hand, that potash could be profitably 
recovered from this source, particularly if some inexpensive means 
were installed along the lines of the process developed at the Santa 
Cruz plant, whereby a mechanical separation of the potash and 
the dust is brought about during the process of collecting. 
The blast furnace, in addition to reducing iron ore to metallic iron, 
is also a gas producer. The gases that issue from the top of the 
furnace are inflammable and have a heat value of from 90 to 100 
British thermal units per cubic foot at standard conditions of tem- 
perature and pressure. It is therefore customary, in order to effect 
economies in the operation of the plant, to utilize this gas. It is, 
however, contaminated by dust which makes burning at maximum 
efficiency difficult. The impurities absorb heat and are also deposited 
in the combustion chambers of the stoves and on the tubes of the 
boilers, where they restrict the absorption of heat. They also 
combine with the brickwork of the stoves, forming fusible compounds 
which result in more rapid deterioration of the bricks. 
The problem, consequently, is presented to the operator of clean- 
ing his gases before their utilization. Most blast furnaces of the 
country are equipped with some kind of cleaner. Many of the 
furnaces have a dry-dust catcher, which is a large vertical steel 
chamber with a conical top and bottom and c} T lindrical center with 
a diameter from 15 to 30 feet. The principle of the operation of the 
dust catcher is merely that of the decreased velocity due to increase 
of area of the conducting pipe, allowing the dust to settle. The 
accumulated dust is discharged through an opening at the bottom of 
the inverted conical bottom. The best dust catchers remove about 
50 per cent of the total amount of dust carried in the gas. This dust 
is high in iron and coke content and contains comparatively little 
potash, that present being largely in the insoluble state. 
The dust not retained in the dry-dust catcher is for the most part 
exceedingly fine in character, the coarser particles having been 
removed in the catcher. The gases containing this fine material are 
