304 Scientific Proceedings, Royal Dublin Society. 



one stream, " The Sulphur Brook," it was calculated to be 129,600 

 grains per minute, or 124,100 lbs. per annum. Subsequently the 

 poor pyrites of the district was calcined and added to the waters 

 in order to enrich it in copper salts. 



During Weaver's management of the mines the method of pro- 

 cedure was practically that just described, but since then it has 

 been considerably modified. The precipitating pits have been 

 replaced by launders, through which the waters are conducted 

 over irons which are strewn along the bottom. These laundeis 

 are sometimes highly inclined, but of late years the tendency 

 appears to have been to reduce the angle of inclination as 

 much as possible, so that now, in many cases, the slope is only 

 sufficient to allow of a steady and continuous flow of the waters. 



General Method of Procedure adopted at the Ovoca Mines. 

 The water, as it issues from the mine adit or pumphead, is con- 

 ducted into a settling pond to allow of the deposition of sus- 

 pended material (ochre, grit, &c.) from which the waters pass to 

 the precipitating launders, which are usually twelve to eighteen 

 inches wide and nine inches deep, set at various inclinations, 

 according to the judgment of those in charge, or as determined 

 by the surface of the ground ; the slopes vary from one in six to 

 one in twelve ; an average would be probably about one in ten. 

 The precipitation works are situated, whenever possible, on the 

 side of a hill or on rapidly falling ground, as this admits of great 

 variation in the slope of the launders. The bottom of the launders 

 is covered for a depth of about three inches, with broken pieces of 

 cast and bar iron, over which the waters (having been freed 

 from suspended material) are caused to pass. Small settling pits 

 (hutches), usually made of wood, and varying in capacity from 900 

 to 1,500 gallons, are fixed at intervals of about 200 yards, and 

 every twelve hours the water is run off from these hutches, and the 

 metals in the launders are brushed over, raked, and again brushed, 

 when the greater part of the precipitate copper which had 

 accumulated on them during the previous twelve hours is carried 

 off in suspension, and run into the hutches, where it is allowed to 

 settle for the next twelve hours, when, preparatory to again 

 brushing the irons in the launders, the water is run off the hutches 

 to within about four inches of the precipitate at the bottom. 

 (See Figs. 1 and 2, Plate XXII.) 



