Examination of the Diopside of Fassa in the Tyrol. 353 



acid. The solution having been evaporated to dryness, and 

 the residuum digested with water and muriatic acid, a large 

 quantity of silica remained undissolved. 



Carbonate of soda precipitated from the solution when cold 

 some oxide of iron with a few traces of alumina ; but oxalate 

 of potash precipitated much oxalate of lime, which was partly 

 ignited and partly mixed with caustic ammonia. A very small 

 quantity of deutoxide of manganese was found mixed with the 

 lime. After this, carbonate of magnesia together with a little 

 manganese was precipitated, by means of carbonate of soda, 

 from the hot solution ; and subsequently, by means of triple 

 phosphate of soda and ammonia, a considerable quantity of 

 magnesia. 



Again, about 2*0 grammes of pulverized diopside were fused 

 with carbonate of soda and l-6th of its weight of nitre. Water 

 gave with the melted mass a greenish solution, which soon 

 completely lost its colour in the air ; and on being tested for 

 the chromic, fluoric, phosphoric and boracic acids, no trace 

 of either was perceptible. 



III. Analysis for the Proportions of the Constituents. 



a. 2' 502 grammes of select and very pure pieces of diopside 

 dried on a hot iron plate, were exposed for three quarters of an 

 hour to a red heat. But the mineral was unaltered in appear- 

 ance and weight, except that its colour turned nearer bottle 

 green. 



b, 2*503 grammes of the diopside finely powdered, were inti- 

 mately mixed with thrice their weight of carbonate of soda freed 

 from water and exposed for half an hour to a moderate red 

 heat The fused mass was dissolved in a moderate quantity of 

 water, placed in an evaporating-dish, and diluted with as much 

 muriatic acid as was necessary to effect a perfect solution. By 

 the evaporation to dryness of the yellowish solution, and by 

 digesting the residuum (which was of the same colour) in water 

 and some muriatic acid, pure white silica was obtained, weigh- 

 ing, after having been dried and heated, 1*3581 gramme. It 

 was completely dissolved in a solution of caustic potash, as well 

 as in a concentrated solution of carbonate of soda assisted by 

 heat ; and after having stood for some time, only a few unim- 

 portant flakes were deposited from this solution. A part of it 

 only was dissolved in caustic ammonia, but the remainder was 

 entirely taken up by carbonate of soda. It will be worthy of 

 a distinct investigation to ascertain the cause of this pheno- 

 menon *. 



* Dr. C.F. B. Karsten has also mentioned the facility with which silica is 

 dissolved in caustic ammonia. See Poggendorff 's Annalen, Band vi. p. 357. 



New Series. Vol. 3. No. 17. May 1828. 2 Z c. The 



