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 nearly 
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 found 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 are rich but difficult to reduce, and are never used except when mixed with 
5 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 belongs 
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 Bechets 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, (Traite des Essais par la Voie Seehe tom. 2, p. 474,) 
describing assays of the sulphurets of copper mixed with iron, (such as the workable 
ore3 usually are,) and after noticing the roasting in which it is necessary to stir the 
particles of ore continually, so that all should come in contact with the air, says; 
st That when the roasting is somewhat 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 deeomposion. When the sulphurous 
acid ceases to be disengaged, a white heat should, for some minutes, 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 dux, will give 
nearly all the copper which it contains, and the iron will remain disseminated 
through the slag, partly in a metallic state and partly in a state 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 vender 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 this class, when they are mixed with much iron. 
Swansea contains about 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 is consumed. The Welsh coals are less bituminous and agglutinating than 
