Chemical Science. 177 



This precipitate is to be carefully washed with water, containing 

 a few drops of hydrosulphuret of ammonia, until all the tartrate 

 is removed ; it is then to be dissolved in muriatic acid, heated 

 to drive off the sulphuretted hydrogen, treated with nitric acid to 

 peroxidize the iron, and then precipitated by ammonia : in this 

 way the iron is procured. The titanic acid may be separated from 

 the solution, (if it contains no fixed parts,) by evaporating to dry- 

 ness, and heating red hot in contact with air, until all that is vo- 

 latile is dissipated, and the charcoal is burnt off. This is best 

 done in a small platina crucible in a muffle ; titanic acid remains. 

 This method appears to be equally advantageous for the prepa- 

 ration of titanic acid from minerals containing it, combined with 

 protoxide of iron, and which may be dissolved in strong muriatic 

 acid, after having been pulverized. As there is then no occasion 

 carefully to wash the sulphuret of iron, that labour is saved, and 

 the process becomes as short, or shorter, than any other known. — 

 Ann. de Chim.xxix. 130. 



10. Wohler on Tungsten, and its Combinations. — M. Wohler 

 prepares his tungsten by fusing together pulverized wolfram and 

 carbonate of potash ; the tungstate of potash is dissolved out by 

 water, muriate of ammonia is added, the whole is evaporated to 

 dryness, and heated red hot in a Hessian crucible. The mass dis- 

 solved in hot water leaves a heavy black powder, being the oxide 

 of tungsten. It should be boiled in weak solution of potash, and 

 washed in hot water. It is readily converted into tungstic acid by 

 heating it in an open crucible ; it takes fire, and burns vividly 

 into a yellow powder. 



Oxide of Tungsten. — Tungstic acid, heated in hydrogen gas, as 

 Berzelius has shewn, becomes first blue, then of a deep brown co- 

 lour ; the substance produced has a lustre almost metallic, and 

 when polished takes the colour of copper. Tungstic acid, in con- 

 tact with zinc in dilute muriatic acid, also becomes blue, and ul- 

 timately forms films of a fine copper-colour. In this state the sub- 

 stance exists as an oxide, and must be retained under water ; if 

 exposed to air it becomes blue again, and ultimately yellow tung- 

 stic acid. The black powder obtained above appears almost as; 

 the metal, when compared with this substance, and when rubbed 

 with a polisher, takes a white metallic lustre. It is> however, 

 only oxide of tungsten, as is shewn by the increase of weight 

 when burnt ; it inflames in the air much beneath a red heat, and 

 100 parts absorb 8 parts of oxygen in becoming tungstic acid, 

 the same quantity as is absorbed by the brown oxide ; whilst me- 

 tallic tungsten requires, for every 100 parts, the addition of 2£ 

 parts of oxygen to become tungstic acid. 



A singular and, as yet, inexplicable phenomenon, occurs in the> 

 preparation of oxide of tungsten from tungstic acid, by hydrogen,. 



Vol. XX. N 



