^08 Scientific Proceedings, Royal Dublin Socieiy. 



out at the top to fit the rope (see Plate XXIII., Figs. 3 and 4), these 

 were driven either into the roof or into one wall of the drift, and 

 were placed at intervals of eight or ten feet where the run was 

 straight, but on curves were more numerous. To run on this, two 

 small grooved wheels were connected together from centre to centre 

 by a small iron plate, a strap embraced each wheel and was terminated 

 at the lower end by a hook, from which a box about two feet 

 long by fourteen inches wide and fourteen inches deep, was sus- 

 pended (Fig. 2, Plate XXIIL), this could contain about three cwt. 

 of cast-iron or of precipitate, and could be easily propelled by a 

 boy. This arrangement was found to answer admirably, and 

 only under the most exceptional circumstances left the track. 



In the adit and main levels the launders were laid on sleepers 

 stretched from wall to wall near the bottom, but leaving a space 

 underneath for overflow or excessive floods (Fig. 5, Plate XXIIL) 

 The sides of the launders sloped outward, and were supported 

 laterally by the blocks of wood on which the tramway rails were laid; 

 a -small waggon on these rails was thus placed over the launders, 

 and from it the metals were distributed to the launders, or the pre- 

 cipitate cleaned up into it ; by fixing a revolving brush to one of 

 these waggons a rapid means of sweeping the metals was secured. 



The method just described, is well adapted for treating the 

 water underground, where the drifts are tolerably level and the 

 water of average richness, but, as previously stated, there is some 

 difficulty in extracting the last portions of the copper when the 

 waters deposit ochre. Precipitation of copper underground is 

 then at an end, unless there is some rapidly falling drift to run 

 the water through, for, it is remarkable, that this semi-spent 

 water, if kept in a state of rest or slow motion, will deposit ochre 

 on the metals in the launder and protect them from further action 

 of the waters f but, if allowed to fall for a short distance on the 

 metals copper will be again precipitated, or if the inclination of 

 the launder is increased so that the water passes briskly over the 

 metals, the same result will be obtained, more especially if wrought- 

 iron is substituted for cast, and the greater the velocity of the water, 

 provided it is not strong enough to wash aM^ay the copper, the 

 better will be the result. At surface, then, if this apparently spent 

 water be run down a steeply inclined launder containing angular 

 stones and fragments of iron, so as to become thoroughly agitated^, 



* Compare page 31 G. 



