NOTES FROM THE U. S. BUREAU OF MINES.*

FIRING OF REFRACTORY WARES.

By G. A. Bole and Others.

THE Bureau of Mines has brought to a close an investigation begun in 1923, of problems in firing refractories, that was under- taken at the urgent request of, and conducted in coijperation with, the Refractories ?\llanufacturers’ Association. The primary objects of the study were to increase the efficiency of burning conditions in the plants, and to obtain data on fundamental con- ditions of operation. The three principal objects with regard to each plant were production of better ware, saving of fuel, and increased kiln turnover.

The work was conducted by means of test runs at the plant, supplemented by laboratory tests in the laboratory car Holmes, and the ceramic station at Columbus, recently transferred to the Bureau of Standards. At most of the plants tested, the changes that were made by the bureau engineers in the operation of the kilns resulted in reducing the time of burning, 13 to 35 per cent., with an average of 19 per cent. At the same time, large savings in fuel were effected, in one plant as much as 43 per cent., the average being 13.5 per cent. for the plants tested, as compared with former practice. These economies were effected without any sacrifice in quality of ware; on the contrary, the quality was improved in many of the tests. Further details are given in a report in course of publication by the Btxeau of Mines.

QUARRY PROBLEMS IN THE LIME INDUSTRY.

By Oliver Bowles.

LIME is a product of tremendous importance in modern industry, in agriculture as fertilizer, in building construction, and in numerous other industries. The annual production of limestone used in lime manufacture is between eight million and nine million tons. In 1922 the Bureau of Mines, at the request of the National Lime Association, began a study of limestone quarrying with the object of promoting more economical methods of operation, and utilization of waste material. In this work, recently completed,

* Communicated by the Director.

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510 U. S. BUREAU OF MIXES NOTES. [_l. F. I.

field studies were made at many quarries, supplemented by obser- vations on lime practice. Much information has been obtained on methods of stripping, drilling, blasting, loading, and transpor- tation. The results of the study will be published as a bulletin wherein the methods employed are compared and the best working principles shown, in order to assist lime manufacturers in improv- ing their practice and in conducting quarrying on the most economical and efficient basis.

RATE OF COMBUSTION OF COAL-DUST PARTICLES.

By C. M. Bouton and J. H. Hayner.

WHILE large-scale tests by the Bureau of Mines and other agencies studying methods of preventing coal-mine explosions have shown that coal dust is explosible and that rock-dusting is a practical means of rendering coal dust inert, the exact nature of the mechanism of an explosion of coal dust and air is not known. The Bureau of Mines has recently completed a second series of experiments which has for its, object the gathering of data that will be of direct aid in determining the exact nature of the propa- gation of a dust explosion. In the first series, a method of accurately sizing the fine coal dust for experiment was developed by floating the finer particles away from the coarser by means of gentle air-currents. In the present series, data were obtained on the relative inflammability of the different sizes thus obtained. The tests show that inflammability does not increase indefinitely as the particle size decreases, but approaches a maximum at a definite size and then falls off. Formerly, it had been generally accepted that explosibility of a dust increases with fineness. The data will be applied in further experiments being conducted along this line, and are being published more fully as a cooperative bulletin of the Carnegie Institute of Technology.

Native Copper.- The chemistry of the deposition of native copper from ascending solutions is discussed1 in great detail by ROGER C. WELLS (U. S. Geol. Survey Bull. 778, 71 pages, 1925). Four theories have been proposed to explain the deposition : Cooling, dilution, fractional oxidation of copper sulphide, and neutralization and reduction. In the application of these theories, the essential conditions of each ore district must be considered. Wells also reports the results of 165 original experiments on the deposition of copper.

J. S. H.