1904.] SMITH AXD EXNER — ATOMIC WEIGHT OF TUNGSTEN. 127 



ammonium salt, as an ammonium iron-manganese tungstate. 

 Laurent^ states that the mother liquor from ammonium tung- 

 state contains such a salt. He ascribed to it the formula: 

 [i2(NHJ,0, 6MnO, zFeA, 3H2O, 45WO3, 8iH,0].^ 



''Borch' analyzed this salt with the following results: WO3 

 84.4%, (FeA + MnA) 4-6%, NH, 40%, ILO 7%. Laurent 

 states that this complex salt is soluble in water and ammonia, and is 

 peculiar in that ordinary reagents do not show the presence of 

 iron, manganese or tungstic acid ; further, that the salt is only 

 broken down by prolonged boiling in acids or alkalies, and then 

 the ingredients can be readily detected. 



" Schneider" recognized the presence of this salt in ammonium 

 tungstate, and stated that it was not removed after five or six 

 recrystallizations. Also that it could not be removed by the 

 ammonium sulphide treatment, for slight amounts of the sulphides 

 of iron and manganese are soluble in the tungsten sulpho-salt. 

 Berzelius^ stated that the sulphides of tungsten, iron and manganese 

 form a compound which is partly soluble in water. 



''To remove this complex salt Schneider, purified his material 

 in the following way: Tungstic acid, obtained from the sulpho-salt 

 of tungsten, Avas boiled in aqua regia, and washed in acidulated water 

 till free from iron. This was dissolved in dilute ammonia, and the 

 solution precipitated by boiling hydrochloric acid, the resulting 

 tungstic acid boiled in aqua regia and again washed. This oxide 

 was again dissolved in ammonia and again precipitated. After 

 reprecipitating three times in this manner, tungsten trioxide was 

 obtained free from iron. However, on dissolving the oxide in 

 potassium hydroxide, a slight brown residue remained which had 

 escaped all earlier tests. This he assumed was not enough to affect 

 the result of his work. 



''Had he applied the sodium carbonate test, this residue would 

 have been larger. In the recent repetition of his work,* he used 

 material purified in precisely the same manner (in fact some of the 

 original material), with the exception of the treatment for the elim- 

 ination of molybdic acid. 



" Borch' recognized this complex salt, and tried to remove it by 

 fusion with potassium carbonate. 



"Later investigators seem not to have appreciated the difiiculty 

 of eliminating it. It crystallizes in part with the ammonium tung- 

 state, and can scarcely be entirely removed by recrystallization. 



^ J. prakt. Ch., 42, 126 (1847). 

 2 Coniptes rendtis, ji, 693 (1850). 



*J.prakL Ch.,so, 152 (1850). 

 ^ Fogg. Ann., 8, 279 (1826). 

 ^J.prakt. Ch., iGi, 288 (1896). 

 ^J.prakt. Ch.,j4,2SA (1851). 



