422 



REPORT OF NATIONAL MUSEUM, 1899. 



From this shale potash-alum was formerly made near AVhitby and 

 Redcar, the aluminum sulphate being- extracted from the shale, and the 

 potash-salt being- added. The trade which since the days of Queen 

 Elizabeth has been largely carried on, has now almost passed away, as 

 alum is now manufactured in other places from coal-shale. Alum 

 works formerly existed at the Peak, Robin Hood's Bay, Stow Brow, 

 Sandsend, Kettleness, Lofthouse (Loftus), Osmotherly, etc' 



According to F. Stolba.~ the so-called Bohemian fuming sulphuric 

 acid is made from vitriol obtained from Silurian pyritiferous schists 

 (" vitriolschiefer ''). The method as given is as follows: Large masses 

 of the schist, which consist essentially of a quartzose matrix contain- 

 ing pyrite, carbonaceous matter, and clay, are exposed to the weather- 

 ing action of the atmosphere for three years. The products of oxida- 

 tion so formed are ferrous sulphate and sulphuric acid, which latter 

 acts energetically upon the clay, and finally aluminum sulphate and 

 other sulphates are yielded. The ferrous sulphate at tirst formed be- 

 comes by oxidation ferric sulphate, which, together with the aluminum 

 sulphate, is the principal product of the weathering of the vitriol slate. 

 Ferrous sulphate remains only in small quantities. The next operation 

 is lixiviation of the mass with water, after which the liquor obtained 

 is concentrated to a density of -iO ' Baume, and finally evaporated 

 in pans until, on cooling, a crystalline cake of vitriol stone is obtained. 

 The vitriol stone is now calcined in order to remove the greater part 

 of its water. The resulting product, when heated to a very high tem- 

 perature in clay retorts, yields sulphuric anhydride, and a residue, 

 termed colcothar, remains in the retorts. The composition of vitriol 

 stone and colcothar will be seen from the following analyses: 



VITRIOL STONE. 



FejOa 20. 07 



AlA - 4. 67 



FeO 0. 64 



MnO Traces. 



CaO 0.14 



MgO 0.89 



K.,0 0. 07 



Na./) 0. 05 



CuO 0. 10 



SiO, 0. 10 



P./)5 Traces. 



RO3 40.51 



As Traces. 



H.,0 32. 58=99. 32 



VITRIOL STONE. 



Fe,{SO,), 50.17 



AlASO,), 11.94 



FeSO, 1.35 



MgSO^ 1.17 



CaSO, 0. 33 



CUSO4 0. 20 



KjSO, - 0. 13 



Na^SO^ 0. 11 



H2SO, 1.49 



MnO, As, and P.,05 Traces. 



SiO^ 9.10 



H.,0 32. 31=99. 29 



^The Geology of England and Wales, p. 279. 



■■'Journal of the Society of Chemical Industry, V, 1886, p. 30. 



