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with copper. I was an eye-witness to the change in 

 all its progress ; and so were thousands besides. I 

 saw the masons laying a chain of new stone troughs, 

 for the copper water to run through, I saw the men. 

 also laying the iron bars, on wooden rafters, in those 

 troughs. I saw the iron bars lifted out of some 

 troughs, where they had lain from one to eight months, 

 and saw them incrusted over with copper, and corro- 

 ded more or less, (some of them to very thin plates), 

 according to the time they had lain in the water. I 

 saw some of the troughs emptied, wherein the bars 

 were wholly dissolved, and the labourers were throw- 

 ing up with shovels the copper, which lay on the 

 stones in the bottom of them. It was like mud, as 

 it lay wet in the heap, but became dust as it dried. I 

 also saw several pieces of copper, which had been 

 made out of their copper-mud. 



a This water is supposed to flow over a vein of 

 copper in the neighbouring mountain. It is of a 

 sharp, acid taste, and of a blue colour. It is received 

 and collected in those troughs, wherein the iron bars 

 are placed; which after lying in the water, often not 

 above three months, are entirely consumed ; then at 

 the bottom of the troughs, a quantity of copper is 

 found, in the form of coarse sand. And it is remark- 

 able, that there is a greater quantity of this copper, 

 than there was of iron. 



u But by what principle is this effect produced ? 

 In order to discover this I made the following ex. 

 periments. 



* c 1. Some small iron nails put into the water, 

 were in four minutes covered with a substance of a 

 copper colour. And during that time the nails gained 

 four grains in weight. The water had the Very same 

 effect on silver and tin. But not on gold. Hence 

 we obserre, the colour and increase of weight were 

 owing to the adhesion of the particles of the matter 

 dissolved in the water by an acid;- which could not 

 penetrate gold. ' 



4i 2. In order to determine the quantity and qua* 



