Chemical Examination of American Green Feldspar. 283 



trapp formation [Trappgebirgsarteii) in the central chain of 

 the Apennines, although Ferber * and some other writers have 

 advanced an opposite opinion. 2d, That the true volcanic 

 formations are found only on the south-eastern side of Italy, 

 with the exception of the extinct volcanic mountain Vulture. 

 The greatest extent of the volcanic rocks is in the line of those 

 of more remote origin, and but a part of them, as Vesuvius, 

 the extinct volcanoes of Nemi and Albano, and the formation 

 near Borghetto, approach the Apennine limestone. 



XLIX. Chemical Examination of Green Feldspar from Be- 

 verly, Massachusetts. By J. W. Webster, M.D.f 

 TTHS mineral is peculiarly interesting, as another instance 

 -*■ of the great similarity existing between the minerals of 

 this country and those of the north of Europe. The only 

 specimen which I have seen from this locality is connected 

 with quartz and mica, constitutng a perfectly characterized gra- 

 nite. The colour of the feldspar is of a lively verdigris green, 

 the fracture is foliated with a high degree of lustre, and the 

 concretions, or imperfect crystals, are from a quarter to half 

 an inch in diameter. The intermixture of the quartz, which 

 is white, with the brown mica and the green feldspar pro- 

 duces a beautiful effect. 



My first object in submitting the green feldspar to a che- 

 mical examination was to ascertain the proportion of alkali it 

 might contain. For this purpose, one hundred grains reduced 

 to an impalpable powder were mixed with twice their weight 

 of boracic acid, as proposed by Sir H. Davy. The mixture, 

 after fusion in a platina crucible, was digested in dilute nitric 

 acid. After separating the siliceous earth, the bulk of the so- 

 lution was reduced by evaporation, supersaturated with car- 

 bonate of ammonia, and boiled ; after filtration, nitric acid 

 was added to the liquor, which was again filtered, and exposed 

 to a temperature sufficient to decompose the nitrate of am- 

 monia that had been formed. The salt obtained was nitrate 

 of potash, and weighed 23-6 grains, equivalent to 11*1 of 

 alkali. 



Another portion of the specimen was treated in the usual 

 manner. The details of the processes it is unnecessary to re- 

 peat, as they presented nothing peculiar. The composition 

 of this feldspar was found to be as follows : 



• Briefe aiis Walschland, p. 430. 



+ From the Boston Journal of Philosophy and the Arts, Nov. 1823. 



N n 2 SUex 



