§iO^ Scientific Proceedings, Royal Dublin Society. 



the precipitate they are protected from contact with the copper 

 sohition. It will be found, that where this system is practised, 

 not only is the proportion of iron required to produce a ton 

 of fine copper very high, but the precipitate is always of low 

 quality and mixed with phosphorus and deleterious ingredients. 



Thirdly, concerning the sifting and drying : Numerous small 

 scales and grains of copper find their way to the waste heap 

 along with the small pieces of iron sifted out in this process, in 

 fact this refuse consists principally of cast-iron, oxide of iron 

 graphite, and copper to the extent of from 4 to 12 per cent. ; this, 

 however, might be recovered if the broken pieces of cast-iron 

 were carefully freed from rust and returned to the precipitating 

 shoots to be thoroughly dissolved. 



When the precipitate is heated not only is the water driven off 

 but the copper is oxidized to a greater or less extent, so that it is 

 a question whether there is anything gained by this process of 

 drying, for, in the first place, the precipitate loses 5 to 10 per 

 cent., while the amount lost in dust, &c., during the drying and 

 packing is often considerable, and attended with very injurious 

 consequences to the health of the v/orkmen. 



Methods of Precipitation adopted under Special CircuTnstances. 



In some of the mines of this district, particularly in those of 

 Cronebane, precipitation of the copper underground has been 

 successfully carried out, and, although the liquors cannot be so 

 thoroughly exhausted as at surface, yet there are many advantages 

 to commend the adoption of this method — Firstly, the waters are 

 taken fresh from the " stulls " and workings, and the copper is 

 extracted before the liquors are contaminated by extraneous 

 matter, or before ferric sulphate or basic salts are formed ; secondly, 

 the water being of a higher temperature (sometimes up to 70° F.), 

 precipitation is more rapid and efficient, with a richer precipitate. 



In the Cronebane mines, peculiar tanks were adopted (See Figs. 

 8 and 4,Plate XXII.), with great ad vantage in economizing space, these 

 tanks were two feet deep and eighteen inches wide, and of lengths 

 varying according to the space to be occupied ; at every four feet, 

 divisions (/)were placed that extended from the bottom to within 

 six or eight inches of the top, between each two of those divisions a 



