Aug., 1926.] U . S . BUREAU OF MINES NOTES. 249

methods similar to those used in coal mining will be used. In the eastern states where the black oil shales of a cannel-coal nature overlie coal seams near the surface, and elsewhere where condi- tions permit, stripping or quarrying methods may be feasible.

The dust produced in Scottish shale-mining operations, accord- ing to some investigators, is non-inflammable and non-explosive. However, this must not be taken to indicate that oil shale of simi- lar characteristics will be encountered in American shale mines. The results of the present tests show that oil-shale dust may present a source of danger in American mines, particularly when comparatively rich material is being worked. Further details are shown in Serial 2758 of the Bureau of Mines.

MAGNETIC C O N C E N T R A T I O N OF F L U E DUST OF T H E B I R M I N G H A M DISTRICT.

By Oscar Lee, B. W. Gandrud, and F. D. DeVaney.

LOSSES of iron ore through the Production of flue dust vary between wide limits in different furnaces, and depend on a number of factors, such as size and design of furnace, amount of fines in the ore, the operating conditions and the blast pressure. Blast- ftlrnace operators of the Birmingham district keenly realize this waste. The ores are comparatively low grade and require more fuel than is ordinarily used elsewhere. Hence the flue dust is low in iron content and high in coke. As a result it is not in suitable condition for direct sintering. In many other iron and steel cen- tres direct sintering is a common practice.

The operators of the district are endeavoring to prevent this waste, and at their request the Southern Experiment Station con- ducted an investigation of methods of recovering flue dust.

The charge and the operating conditions at the various fur- naces from which samples were obtained are so variable that no single sample of flue dust can be taken as representative. Like- wise samples from the same furnace varied greatly in physical characteristics and in chemical composition. Hence a successful concentration process must be capable of operating under a varying feed.

The coke can readily be removed by gravity concentration, for example, hydraulic classification. However, after the coke has been removed the remaining low-grade iron ore is not amenable

250 U . S . BUREAU OF ),lINES NOTES. [J. F.I.

to satisfactory concentration by ordinary methods. This is due primarily to intimate interlocking which requires grinding to ioo mesh to liberate the hematite from the gangue. Material of such fineness is difficult to handle by gravity concentration.

In a number of the samples hot reducing gases in the blast furnace or in the dust catcher had converted the iron minerals from hematite or limonite into magnetite. When such an altera- tion had taken place, a good separation of the iron mineral from the gangue can be obtained by use of magnetic concentra- tion machines.

Magnetic concentrators of various kinds, such as a magnetic wet cobber, a magnetic dry concentrator, and a magnetic log washer, were used on flue dust in which the iron mineral had been converted into magnetite. The first two machines are built to handle coarse material, and the log washer is designed to handle fine material. The results obtained with these different machine~ show that a good concentrate and a high recovery can be made by the dry concentration or the wet cobber without preliminary crushing. It is doubtful whether the added expense of fine grinding would be justified by the higher grade of concentrate obtainable in the magnetic log washer. Additional information is contained in Bureau of Mines Serial 276I recently issued.

The Application of Radiography to the Study of Capillarity. E. A. OWEN and A. F. DUI,'TON. (Proc. Phys. Soc. London, April 15, I926.)--Copper tubes well amalgamated within and thoroughly cleaned were held in a vertical position with their lower ends dipping into distilled mercury. The liquid rose in the metal tubes as water rises in glass capillary tubes. By an X-ray tube a metre distant a radiograph of each tube was taken upon a plate or film close behind it. Thus a permanent record was secured from the measurement of which the surface tension of mercury was calculated. At I7 ° C. this was 485 dynes/cm. The same method was applied to photo- graphing the rectangular hyperbola formed by mercury rising between two vertical plates of copper in contact along a single vertical line and making a small angle with each other. Radiographs were obtained of the depression of mercury in three small steel tubes.

In the discussion that followed the paper a speaker stated that a manufacturing firm had proposed to him the problem of reading the height of the mercury in a piezometer tube of steel surrounded by a water jacket, the walls of the tube being 4 mm. thick and the bore 8 mm. He got a sharp image of the mercury meniscus by using an X-ray tube with its focus 45 in. from the mercury. An exposure of IO secs. was given. G . F . S .