Determining Columhium and Tantalum. 



397 



0-32 per cent columbic oxide. These values were calculated 

 from the densities. The original intention was to make mix- 

 tures of the oxides at intervals of ten per cent. Irregularity 

 in the curve showing change in density with change in com- 

 position when there was over 60 per cent of tantalic oxide 

 caused us to repeat some of the determinations in this region, 

 as we suspected an error in the woi-k. We were led to the 

 conclusion that in the mixtures containing a moderate excess 

 (65-85 per cent) of tantalic oxide, the densities are not as 

 constant as when other proportions are present. The table 

 and curve given below will make this clearer. All the results 

 which were obtained upon known mixtures are tabulated 

 below with one exception. This result was obviously in error 

 as the density was not approximately related to the compo- 

 sition. In most cases, the density of one mixture of any given 

 composition was determined. Where the curve as plotted 

 from the table showed irregularities, duplicate mixtures were 

 made and the results enclosed in bi-ackets in the table. All 

 densities are referred to water at 20°. 



Composition 

 % TaaOs 









Specific gravity 



Average 



4-555 



4-549 





4-552 



5 



4-652 



4-647 





4-650 



10 



4-744 



4-748 





4-746 



20 



4-929 



4-929 





4-929 



30 



5-203 



5-197 





5-200 



40 



5-474 



5-474 





5-474 



50 



5-852 



5-847 





5-850 



60 



6-437 



6-431 





6-434 



65 



6-719 



6-763 



6-730 



6-737 



j 70 

 " 70 



7-189 

 6-958 



7-170 

 6-992 



7-008 



6-981 [ "^'^^^ 



75 



7-431 



7-452 





7-441 



80 

 80 



7-629 

 7-662 



7-637 ] 

 7-687 1" 





7-654 



85 

 85 



7-885 

 8-01 



7-925 

 7-99 



7-963 ) 



7-961 



90 

 90 



8-103 

 8-090 



8-078 

 8-092 



8-133 ) 



8-098 



95 



8-245 



8-241 





8-243 



100 



8-725 



8-684 



8-730 



8-716 



The average of the results in the table are plotted in the 

 figure. 



The curve has some interest from the standpoint of solid 

 solutions. The fact that the points as plotted do not lie on a 



