192 REPORT OF NATIONAL MUSEUM, 1899. 



natural oxidation takes place, whereby the sulphide is transformed 

 into a hydrated sulphate. The latter being soluble runs off in solution 

 in the water, which must be collected and evaporated in order to obtain 

 the salt. Thus prepared the sulphate is used in dyeing, in the manu- 

 facture of writing ink, as a preservative for wood, and as a disinfectant. 

 It has also been used in the manufacture of certain brands of fertilizers. 

 The method of manufacture as formerly carried on at Strafford, 

 Vermont, is given below: 



The process consists in first raising the ore from the bed, which is principally done 

 with the help of gunpowder. The blocks of ore are then broken up into small pieces, 

 to facilitate the decomposition, by suffering the oxygen contained in water and the 

 atmosphere to come more directly in contact with the material composing the ore. 

 Large heaps of these pieces, called leaches, are made upon a tight plank bottom or 

 upon a sloping ledge of solid rock, where the liquor or lye that subsequently runs from 

 them may be saved. 



In dry weather a small stream of water is made to flow upon and penetrate these 

 leaches in order to produce a spontaneous combustion, which in warm weather com- 

 mences in a few days, and if properly managed will continue several weeks. When 

 combustion is taking place great care is requisite in order to have the work go on suc- 

 cessfully, for if too much water is suffered to penetrate the leach or heap the decom- 

 position is checked by the reduction of temperature and the lye or liquor issuing from 

 it is too weak to be valuable, and if there is not water enough put on the leach the 

 decomposition is also arrested by the absence of the oxygen found in the water, 

 which is necessary to convert the sulphurous acid into the sulphuric, that sulphate 

 of iron or copperas may be produced. 



The liquor that runs from the leaches is collected in reservoirs, from which it can 

 be taken at pleasure. Below the reservoirs upon the hillside buildings are erected, 

 called evaporators, to which liquor is conducted in troughs from the reservoirs in 

 small streams that are divided and subdivided by means of perforated troughs, 

 brush, etc. Several tiers of brush are arranged in the building, through which the 

 liquor is made to pass to facilitate the process of evaporation. In dry, windy weather 

 the evaporation is oftentimes so rapid that the brush and other substances with 

 which the liquor comes in contact during the latter part of its journey often have an 

 incrustation of copperas formed upon them; but upon the return of rainy weather the 

 humid atmosphere checks the evaporation, and the crust of copperas is dissolved and 

 passes with the liquor into reservoirs prepared to receive it. 



The liquor, which is now very strongly impregnated with copperas, is conducted 

 into leaden boilers, where heat is applied and the liquor redi-ced to a strength indi- 

 cated by the acidimeter to be right for the production of copperas. The liquor is 

 then placed in vats of lead or of brick and water cement, called crystallizers, and 

 after remaining from eight to ten days a crust of copperas is formed upon the bottom 

 and sides of the vats, composed of nicely formed crystals. The water remaining in 

 the crystallizers is then pumped back into the boilers, the crust of copperas removed, 

 and, after being sufficiently drained, it is packed in casks ready for market. 1 [See 

 also under Alum shale and vitriol stone, p. 421.] 



The analyses given below show (1) the composition of fresh pyrite 

 from the Coal Measures of Mercer County, Pennsylvania, and (2) and 

 (3) that of two varieties of paint produced from it by calcination. 2 



Geology of Vermont, II, 1861, p. 830. 



2 Report M. M. Second Report of Progress in the Laboratory of the Survey at Har- 

 risburg, Second Geological Survey of Pennsylvania, 1879, p. 374. 



