236 THE ATOMIC WEIGHTS. 



TANTALUM. 



The results obtained for the atomic weight of this metal by Berzelius,* 

 Rose,f and Hermann J may be fairly left out of account as valueless. 

 These chemists could not have worked with pure preparations, and their 

 data are sufficiently summed up in Becker's " Digest." 



Blomstrand's determinations, as in the case of columbium, were 

 made upon the pentachloride. His weights are as follows : 



Ta. 2 Or,. AgCl. 



.9808 .598 ...... 



1.4262 .867 2.906 



2.5282 1.5375 5.0105 



1.0604 . 6 455 2.156 



2.581 i.577 ...... 



8767 -534 



Hence the subjoined percentages of Ta 2 5 from TaCl 5 , and the ratios 

 SAgCl : TaCl 5 : : 100 : x, and 5AgCl : Ta 2 5 : : 100 : x. 



Percent. Ta,O 5 . AgCl : TaCl y AgCl : Ta,O- . 



60.971 ...... f ...... 



60.791 49. 78 29.835 



60.814 50.458 30685 



60.873 49.297 29.940 



60.960 ...... ...... 



60.924 ...... 



Mean, 60.889, .0208 49-6ir, =b .289 30.153, dr .180 



From these ratios we get for the atomic weight of tantalum : 



From per cent. Ta 2 O 5 Ta = 172.342 



From 5AgCl : TaCl 5 ; " = 177.055 



From 5 AgCl : Ta 2 O 5 " =174.821 



These results are too low. Probably Blomstrand's material still con- 

 tained some columbium. 



In 1866 Marignac's determinations appeared. || He made four analyses 

 of a pure potassium fluotantalate, and four more experiments upon the 

 ammonium salt. The potassium compound, K 2 TaF 7 , was treated with 

 sulphuric acid, and the mixture was then evaporated to dryness. The 

 potassium sulphate was next dissolved out by water, while the residue 



* Poggend. Annalen, 4, 14. 1825. 



f Poggend. Annalen, 99, 80. 1856. 



1 Journ. fur Prakt. Chem., 70, 193. 1857. 



g Acta Univ. I^und, 1864 



|| Arch. Sci. Phys. Nat. (2), 26, 89. 1866. 



