54 



owing to some failure or difficulty in working the mines, or, perhaps, to the dis- 

 turbed political condition of the South American States. In 1837 it was nearljj 

 one-third of the whole reduction. Copper pyrites, or the bi sulphuret of copper, 

 is the chief ore of that metal which occurs in Devon and Cornwall ; other copper 

 ores being f.iund in comparatively small quantities. The next in importance is 

 the sulphuret or grey ore of the miners. The black ore, or oxide of copper, is 

 sometimes found in sufficient quantities to be worked to advantage. The carbo- 

 nates arc rich but difficult to reduce, and are never used except when mixed with 

 'he other ores. The escape of carbonic acid gas carries with it much of the metal- 

 lic base in a state of sublimation ; but the nature of the different ores belong" 

 properly to another division of the subject, and will be noticed hereafter. 



It is thought that nearly all the metal from the ore is extracted, not losing more 

 than a half per cent, beyond the assay ; but it is not clear that they obtain all that 

 chemical analysis would show. The assay is usually by the dry mode and anala- 

 gous to the process of reduction on a large scale. Since writing the above I have 

 seen Mr. De le Bcche's valuable work on the economic geology of Devon and 

 Cornwall, in which he remarks that " the mode of assaying copper ores is usually 

 conducted in a somewhat rough manner, and accurate results can scarcely be ex- 

 pected from it. Indeed, chemistry has made but little progress among the assayers 

 in Cornwall." He says that it is precisely the same with that described by Price 

 sixty years ago. Berthier, (Traile des Essais par la Voie Seche torn. 2, p. 474,) 

 deicribing assays of the sulphurets ot copper mixed vviih iron, (such as the workable 

 ores usually are,) and after noticing the roasting in which it i.^ necessary to stir the 

 particles of ore continually, so that all should come in contact with the air, says: 

 "That when the roasting is somcwhit advanced that the heat should, from time to 

 time, be increased to a bright red, in order to make the sulphurets and sulphates 

 act upon each other and produce reciprocal decomposion. When the sulphurous 

 acid ceases to be disengag.d, a white heat should, for some niinutes, be produced 

 to decompose the last trace of sulphate. When the roasting has been conducted 

 with care, the assay, melted with 3 or 4 times its weight of black flux, will give 

 nearly all the copper which it contains, and the iron will rBinain disseminated 

 through the slag, partly in a metallic state and partly in a stale of oxide. If the 

 roasting has been imperfect the slag will be sulphurous and retain copper in com- 

 bination. With poor copper ores the slag also retains a good deal of copper, but 

 this loss may be greatly decreased by adding about one part of borax to the black 

 flux, in order to render the scoria more liquid; but it is preferable, in such cases, 

 to assay by the humid way," which indeed Berthier strongly recommends for ores 

 of thii class, when they are mixed with much iron. 



Swansea contains uboul 20,000 inhabitants, nearly all of whom are connected 



with the various manufactories and mines in the vicinity. Besides the copper 



works there are iron works, a pottery, and bituminous coal pits near the town. 



About 500,000 tons of coal are shipped annually from this port, and a very large 



' amount isconsuraed. The Welsh coals arc less bituminous and agglutinating thjn 



