Metallurgical Studies of Rhodonite Ores, Silverton District, Colorado (In Three Parts). Melting, quenching, and acid leaching of concentrates and electrolytic recovery of manganese from solution. 3

Studies were made to determine the effect of the shape of a pneumatic-rock-drill exhaust muffler on its efficiency, and the origin and reduction of exit noise from the mufflers. The report describes the investigation of rock-drill noise abatement.