Abstract: Method and apparatus for Percussive drilling, in which a drill rod is selected with dimensions such that cross-sectional areas of an inner channel within the rod for flushing medium, and of an outer channel formed between the rod and material being drilled, are substantially equal, so that flow resistance of the drill particles and consumption of flushing powder are reduced.

Abstract: There is provided an acid mixture to use as the electrolyte of a galvanic battery of the type in which the electrolyte flows through the battery cells as a liquid solution, said mixture being composed of sulfuric acid and powdered chromic acid. The acids are mixed together to form a paste-like mass which is, when the battery is being used, introduced into the water stream flowing into the battery. Flaky chromic acid may be pulverized by grinding in a ball mill before mixing with the sulphuric acid, or the acid components may be mixed before such grinding.