N O T E S F R O M T H E U. S. B U R E A U O F M I N E S . *

TECHNOLOGY OF SLATE.

By Oliver Bowles.

THE writer recently completed a careful study of about sixty- five active slate quarries and finishing plants in Pennsylvania and Maine; New York and Vermont; Maryland-Pennsylvania, and Virginia.

The chief products of manufacture are roofing slates, black- boards and school slates, electrical switchboards, billiard tables, shower stalls, steps and various other forms of structural slate. Waste constitutes a very important problem in all slate quarry operations, the proportion of waste varying from 65 to 95 per cent. Much study was devoted to improvements, whereby waste could be partly eliminated, and to determine more extended uses for unavoidable waste. Experiments by industrial laboratories indicated that pulverized waste slate could be used to advantage as a filler in road asphalt mixtures, plastic roofing and flooring, and various other products. Many other uses of slate refuse are discussed. However, due to the difficulty of developing a wide market for waste slate, quarrymen should devote their attention primarily to means of eliminating waste to the greatest possible extent. Further details will be found in Bulletin 218, of the Bureau of Mines.

ROCK STRATA GASES IN MINES OF A NEVADA MINING DISTRICT.

By E. D. Gardner.

IRRESPIRABLE gases issuing from the rock formations are a source of expense and danger in some metal mines. There is a great variation in the composition of such gases and, as shown by recent sampling by the Bureau of Mines, the gas may consist mostly of carbon dioxide (" Rock Strata Gases in the Mines of the East Tintic Mining District," by G. E. McElroy, Bureau of Mines Serial 2275), or of methane (" Methane in California Gold Mines," by B. O. Pickard and E. D. Gardner, Bureau of Mines Serial 23o3), or nitrogen, as in the present instance.

* Communicated by the Director.

275