BUREAU O~ MIXES NOTES. COMBUSTION
OF B I T U M I N O U S
By Joseph D. Davis.
SAFE storage of bituminous coal, which is probably the only solution of stabilizing the coal industry, involves means to overcome hazards of spontaneous ignition when coal is stored in large piles. On account of the divergence of opinions and the variety of methods proposed for storing coal, the Bureau of Mines, in co6peration with the Carnegie Institution of Technology, has conducted a laboratory study of the factors involved in spontaneous combustion of bituminous coal. One of the principal objects was to determine why some coals ignite more readily than others. A laboratory test was devised for determining the relative tendency of coals to fire spontaneously, and this " critical temperature " test was applied to many coals. The conclusions reached as a result of this study are that fine coal dust and moist air quickly increase the hazards of spontaneous combustion. Coal finer than 2oo mesh has a critical temperature of I7I ° C., while coal between Io and 2o mesh has a critical temperature of 23 l° C. Coal coarser than one-fourth inch showed no rapid self-heating. Therefore, the presence of fines in a coal pile should be avoided. Moisture in the air or coal facilitates oxidation and consequent heating. Pyrite in lump form has no dangerous effect in coal. i~[ixtures of fresh and partly oxidized coal heat no more rapidly than fresh coal. The " anthraxylon " or " woody " constituents of the coal have a lower critical temperature than the " attritus" constituents, but more investigation is needed to evaluate the readily oxidizable constituents in coal and thus determine which are the more responsible for spontaneous heating. The critical-temperature method evolved for testing coals seems suited for grading their relative tendencies to fire spontaneously, and the Bureau of Mines expects to develop this method further and apply it in a survey of the coals of the United States. Further details will be found in the recent report on this subject, which was published as Bulletin 3 of the Carnegie Institution of Technology. T h e Evaluation of the Colors of the Spectrum in Terms of the T h r e e Primary Colors. R. A. HOUSTOUN. (Phil. Mag., Jan.,
I923.)--" If we take three colors--a red, a green, and a blue--and represent them by the corners of an equilateral triangle, then any