POTASH IN SCHIST* 



XVIII. 



Analysis of a Schist in the Environs of Cherbourg, tak&ii 

 from the Excavations made in Bonaparte Harbour. Bij 

 Mr. Bertiiieu, Mine Engineer** 



the rook de- V^ONSIDEREt) separately, and in small masses, this 

 rock has all the characters of the primitive formation. It 

 is of a dirty green colour, and has the greasiness and lustre 

 of* talc, though in a very slight degree. Its texture is slaty, 

 and a multitude of little grains of crystalline quartz, dis- 

 seminated between its lamina?, are visible to the naked eye. 

 Some have a laminated fracture, and are probably feldspar: 

 we may unquestionably however consider it as of interme- 

 diate formation from its situation. In fact Mr. Descotils 

 has observed, that it contains blocks of granite, frequently 

 pretty large and rounded; and that it alternates with an- 

 cient breccias well characterized, talky and argillaceous 

 schists, &c. , 



It would have been impossible to separate the quartz 

 mixed with it, whatever pains were taken. Besides, the 

 person who sent it to the laboratory desired, that it should 

 be analysed as it was. 



Analysis* Five grammes [77 gi*s.] were fused with double their 



weight of caustic potash, dissolved in pure muriatic acid, 

 evaporated to dryness, and the silex separated. The liquor 

 being filtered, and tested with sulphuric acid and sulphur- 

 etted hidrogen, gave no precipitate. Hidrosulphuret of am- 

 monia formed in it a black precipitate. Being filtered, ox- 

 alate of ammonia, afterward poured into'the liquor, scarcely 

 rendered it turbid ; and potash precipitated a small quan- 

 tity of magnesia. The sulphurets having been redissolved 

 in nitrornuriatic acid, the whole was precipitated afresh by 

 saturated carbonate of potash. Nothing remained in the 

 liquor, which proved the absence of manganese. Lastly the 

 alumine and iron were separated by caustic potash. 



* Journal des Mines, vol. XXI, p. 315. 



The 



