310 M". Weber on the Crystals of the Sulphuric Acid- Chambers, 



acid strongly calcined. This volatilization of tungstic acid 

 belongs to the remarkable phenomena recently discovered by 

 M. St.-Claire Deville, concerning the action of hydrochloric 

 acid on the amorphous oxides, and is explained in like manner*. 



Tnngstate of lime mixed with chalk is changed in a current 

 of hydrochloric acid into neutral tungstate of lime, which cry- 

 stallizes in the excess of chloride of calcium formed. The 

 Scheelite thus obtained had the composition CaOWO 3 , and 

 the crystalline form of the native mineral. 



Debray also prepared tungstate of iron, or Wolfram, by heat- 

 ing to a high temperature a mixture in any proportions of 

 tungstic acid and oxide of iron. All the substance was carried 

 to the cold parts of the tube, where were deposited tungstic 

 acid, magnetic oxide of iron, and tungstate of iron in definite 

 lustrous crystals, identical in shape with those of native Wolfram. 



Various opinions have prevailed as to the composition of the 

 crystals formed in the sulphuric-acid chambers. Some have 

 regarded them as a compound of sulphuric acid and binoxide of 

 nitrogen ; by others they have been considered to be a com- 

 pound of sulphuric acid and nitrous acid ; while Otto assumes 

 that they contain hyponitric acid combined with sulphuric acid. 

 In a recent research, Weltzien has adopted this view, and assigns 

 to them the formula 6S0 2 + 2N0 4 -f 4HO. 



These crystals have been examined by Dr. Weber f. The 

 crystals were prepared by passing dry sulphurous acid into con- 

 centrated nitric acid, kept well cool until the mass had assumed 

 a crumbly consistence ; it was then allowed to drain on a dry 

 porous tile placed under an exhausted receiver. It is important 

 that in the preparation there shall be an excess of nitric acid, in 

 which the crystals are not soluble. 



By the action of hyponitrous acid on English sulphuric acid 

 the same compound is obtained, though less free from adherent 

 acid. To ascertain the composition, determinations were made of 

 the sulphuric acid, water, nitrogen, and of the oxygen. The 

 water was determined by placing at the end of a combustion- 

 tube a layer of ignited magnesia. On this the weighed sub- 

 stance was placed, covered with magnesia, and a layer of copper 

 6 inches long placed in front. The apparatus being heated, a 

 layer of perfectly dry air was passed through the tube, in front 

 of which there was a chloride-of-calcium tube. To determine 

 the nitrogen, the arrangement was the same as in the above case, 

 except that, instead of air, carbonic acid was passed through the 

 tube; and instead of the chloride-of-calcium tube, a gas-delivery 



* Phil. Mag. vol. xxii. p. 515. 



f Sitzungsberichte der Berliner Akademie, February 1862, 



