1826.] new Variety of Wolfram, 331 



tungstate of iron is different from that previously mentioned, for 

 the quantity of manganese does not amount to one-half; but it 

 is remarkable that the quantity of acid is nearly the same. 



Two analyses of common wolfram were performed by directly 

 acting upon it with muriatic acid, and we obtained in one expe- 

 riment 70, and in the other 72 of tungstic acid. The operation 

 is very long and tedious, because the muriatic acid decomposes 

 the last portions of wolfram with difficulty, and also because the 

 .tungstic acid adheres to the sides of the vessel, if it be not very 

 frequently stirred. 



When the acid ceases to become coloured, and the residuum 

 is of a pure yellow colour, it must be washed with water, and 

 afterwards repeatedly treated with ammonia; if there" remain 

 anything insoluble in the ammonia, as most frequently happens, 

 it ought to be white ; this residuum is to be dried and weighed, 

 and its weight deducted from that of the wolfram employed. 

 .This method is inexact, imless we ascertain that the muriatic 

 acid has not dissolved either alumina or lime ; this is undoubt- 

 edly the reason why less tungstic acid was obtained by this 

 method than by potash. 



When wolfram in fine powder is long di2;ested in muriatic 

 acid, it is entirely decomposed ; but in this case, the quantity of 

 acid must be large, and it must be very strong. When the 

 ferruginous solution is poured and mixed with water, it becomes 

 milky, and deposits a flocky yellow matter, which is tungstic 

 acid : when this has been well washed, it would seem that its 

 purity might be depended upon ; it contains, however, a little 

 iron, for if it be dissolved in ammonia, it assumes a bkie tint, 

 and leaves after solution a yellow substance, which is oxide of 

 iron. 



It thus appears that muriatic acid, whether cold or hot, never 

 completely decomposes tungstate of iron : it forms a supertung- 

 state, a portion of which dissolves in the muriatic acid when it is 

 sufficiently strong, and its quantity large ; the reason why 

 tungstic acid becomes blue when it is dissolved in an alkali is 

 imdoubtedly because a small quantity of tungstate of iron is 

 re-formed ; and this being decomposed by the excess of alkali, 

 oxide of iron is left. 



Wishing to know the absolute quantity of oxygen contained 

 in wolfram, I reduced 100 parts of common tungstate by a strong 

 heat; it lost 40 parts. In another experiment made nearly at 

 the same temperature, but longer continued, the loss was 46 per 

 cent. The iron which this mineral contains being 20*745 per 

 cent, would suffer a loss of 4*50 ; and the oxide of manganese 

 being 6'4, it would lose 52 centigrammes, which amount toge- 

 ther to 5*09, the remainder of the loss, amounting to 32"yi, 

 must have been derived from the tungstic acid. 

 • As the oxides of manganese and iron amount together to 



