326 Manufacture of Sulphat of Iron, 



Art. XII. — Some account of the Copperas mines and manu- 

 factory in Strafford, Vt. ; by Dr. John Locke. 



The mine is situated about twelve miles from Dartmouth 

 College, and about five miles from Thetford, Vt. It is near 

 the summit of a hill which rises probably two or three 

 hundred feet above the bed of the streams in the vallies 

 below. 



The gangue in which it occurs is mica slate, the strata of 

 which, are very highly inclined to the horizon, and present 

 their long ridges above the surface in various parts of the 

 hill, particularly at its summit. There are occasionally 

 veins of quartz in the slate. The rocks for several miles 

 around are, as far as I observed, principally mica slate. 

 There are no particular indications of iron at any consider- 

 ble distance from the mass of the mine, but the transition 

 from the slate to the pyritic ore is abrupt. The mine has 

 been opened obliquely up the hill, about twenty rods in 

 length and four in breadth. The ore has been traced near 

 half a mile, running pretty much in the direction of the stra- 

 ta of the slate. 



The ore consists of an aggregate of quartz and undecom- 

 posed pyrites in small grains. In its granular aggregation, 

 the ore resembles the quartz and feldspar in fine grained 

 granite. The pyrites constitutes the greater proportion. 

 Many specimens contain abundance of needle shaped crys- 

 tals of schorl. Its fracture possesses a metallic lustre, and 

 most of it approaches in colour to pale brass, from which it 

 varies to steel grey. 



The ore is very compact and is obtained for manufactur- 

 ing by drilling and blowing. In manufacturing it into cop- 

 peras it goes through the several operations of decomposition, 

 lixiviation and evaporation, each of which constitutes a dis- 

 tinct operation. For several years the manufacturers effect- 

 ed the decomposition in the following manner : the ore was 

 broken into fragments of a foot or less in diameter, and 

 heaped upon inclined scaffolds erected and floored with 

 plank for the purpose. Thus exposed to the actiou of air 

 and moisture it very gradually decomposes at the surface. 

 Thus from the same mass of ore a solution was obtained, 

 year after year, either by the rains or by the application of 

 water by other means. The solution was received from 

 the inclined scaffolds in plank cisterns. 



