136 SMITH AND EXNER — ATOMIC WEIGHT OF TUNGSTEN. [April 7, 



tion. As a rule all of the acid dissolved, and there was at the 

 most a very small residue. Thus forty-five liters of a saturated 

 solution contained a residue which weighed less than two grams. 



The ammonium paratungstate separating from such a solution 

 showed the needles and plates characteristic of that salt. Only the 

 first three fractions were preserved. They represented seven- 

 eighths of the entire substance. The other portions were set aside. 

 A second and a third treatment, as outlined above, was given the 

 first three fractions, and when the salt, finally obtained, was sub- 

 jected to the sodium carbonate test, allowing the solution to stand 

 over night, it remained absolutely clear. The mother liquor from 

 the salt, reduced to five cubic centimeters, remained colorless. 

 One object in this long and baffling study had at last been 

 obtained. We were the possessors of seven hundred grams of pure 

 ammonium paratungstate. 



Three kilograms of impure ammonium paratungstate were decom- 

 posed by acids as described above, the operation being repeated 

 five times, when the ammonium salt from the last decomposition 

 responded admirably to the crucial tests. This salt disclosed none 

 of the substances which were found accompanying the tungstic acid 

 originally, hence the latter was considered pure and was applied as 

 will appear in subsequent paragraphs. However, before proceeding 

 further it seems proper to direct attention to certain other experi- 

 ences which possess interest and value. 



The Residue Obtained by Digesting Tungsten Trioxide 

 WITH Sodium Carbonate. 



Ammonium paratungstate, after three crystallizations and when 

 quite white in color, was ignited in a platinum crucible. Two hun- 

 dred grams of oxide were obtained in this way and were digested 

 with a 2% solution of sodium carbonate of excellent commercial 

 quality. Quite a residue appeared. It was washed and dried. A 

 portion, weighing 0.4712 gram, was digested with aqua regia. 

 The insoluble part weighed 0.4309 gram, while the solution of the 

 soluble constituents, weighing 0.0403 gram, was reduced to a small 

 volume, diluted with water and precipitated with ammonia. The 

 iron weighed 0.0337 gram as ferric oxide. Manganese and plati- 

 num were also found. The tungsten trioxide, when digested with 

 hydrofluoric acid, lost 0.0149 gram, representing silica. Or, if the 

 results be tabulated, they show : 



