VOL. XLVUI.] PHILOSOPHICAL TRANSACTIONS. 36; 



Exp. 4. In order to determine the quantity and quality of the matter in the 

 water, he put 2 drs. of small iron nails into 3 oz. of it, and let them stand 24 

 hours ; then examined, and found the surface of the water covered with a thick 

 scum, like that of a chalybeate spa. It lost the blue colour, and sharp vi- 

 triolic taste. It was quite transparent, and at the bottom there was a quantity 

 of a brown ponderous powder, whif;h, when dried, weighed 14 grs. This pow- 

 der melted without any flux, produced 1 2 grs. of pure copper. The nails lost 

 8 grs. in the water, and were, in several places, covered with a solid lamina of 

 pure copper. The water, in which the nails lay, after being filtrated and evapo- 

 rated, afforded a green vitriol, which in every respect resembled sal martis, and 

 produced the same effects, when dissolved, and mixed with any astringent 

 tincture. 



Exp. 5. From the spring water treated in the same manner, he obtained a 

 blue vitriol, the basis of which is copper. 



From all these experiments he infers, that a mineral acid is the active quality 

 in this water ; which being diffused through the copper ore, unites itself with 

 that metal, and forms a vitriol, which is dissolved by the water, and remains 

 suspended in it, till it meets with iron in the pits, by which this acid is more 

 strongly attracted than by the copper, therefore it quits the copper, corrodes 

 the iron, and changes it into a vitriol, which is again dissolved, and carried off 

 in the stream continually flowing from the pits ; while the copper, deserted by 

 the acid, falls, by its specific gravity, to the bottom of the pits. 



By this account it is evident, that this admirable process is a simple precipi- 

 tation of the copper, by means of the iron. Hence it has been improperly 

 called a transmutation of iron into copper. But, lest any difficulty should still 

 remain, concerning the consumption of the large quantities of iron put into the 

 pits, he adds the following observations, to show that it is dissolved and carried 

 off in the water. 



Observation 1 . The water in the pits are covered with a thick scum, occa- 

 sioned by the air bubbles constantly rising, and bursting on the surface ; which 

 is an evident sign of the solution of the iron. — Obs. 2. The iron is gradually 

 consumed in the pits, and abounds with irregular depressions, like old iron : a 

 strong symptom of its being corroded by an acid. — Obs. 3. The channel of the 

 stream running from the pits is furred with red ochre, which, after being roasted 

 in a strong fire, was attracted by the magnet. As this ochre is only found in 

 the stream below the pits, it appears to be part of the iron dissolved in the 

 water. — Obs. 4. The quantity of copper found in the pits, after the iron dis- 

 appears, is generally greater than that of the ii*on when first put in : for the 

 proprietors assured him, that sometimes a ton of iron will produce, or rather 

 precipitate, a ton and half of copper. This fact alone would be sufficient to 



