396 Gooch and Phinney — Quantitative Determination 



These results make it plain that when the comparison is 

 made between solutions of pure rubidium chloride the spec- 

 troscopic method is capable of yielding fair approximations to 

 truth. In the practical determination of rubidium, however, 

 the question of the effect of the presence of sodium and potas- 

 sium which naturally accompany it is of importance. .Atten- 

 tion was therefore turned next to the consideration of this 

 point, and the record of observations as to the influence of 

 sodium upon the brightness of the rubidium spectrum is con- 

 tained in the accompanying tabular statement. 



Standard. 

 Rubidium in a coil- 

 full (5V cm 3 ). 



Test solution. 



Sodium in a 



coil-full. 



0-00066 ms. 



0-00026 nig. 



0-00260 " 



j 0-00130 " 



( 0-00260 " 



\ 0-00260 «' 



{ 0-00520 " 



0-00260 " 



0-00660 " 



0-00260 " 



0-00780 " 



0-00260 " 



0-01500 " 



Comparison of 

 lines of test by 

 pairs. 



Slightly brighter. 

 Slightly fainter. 



Equally bright. 



Comparison of 



lines of test with 



standard. 



y Brio-hter. 



Brig-liter, 



>- Equally bright. Brighter, 



Brighter. 

 Fainter. 

 Brighter. 

 Fainter. 

 Brighter. 



Invisible on account 

 of glare. 



Brighter. 



Brighter. 

 Brighter. 



Invisible. 



It appears that within limits the presence of sodium in the 

 flame increases the brilliance of the rubidium spectrum. The 

 brightness of the lines is raised under the conditions to a maxi- 

 mum by the presence of sodium to forty per cent of the 

 weight of the rubidium, and increase in the amount of sodium 

 does not further influence the brightness of the lines until the 

 proportion of sodium to rubidium is as ten to one; or, speak- 

 ing broadly, the difference between the dissociating effect of 

 sodium upon the rubidium chloride (to which we attribute the 

 effect noted) does not appear to be materially different whether 

 one or a score of molecules of sodium chloride are present to 

 one of the rubidium chloride. But when the proportion of 

 sodium to rubidium much exceeds ten to one the glare of light 

 diffused through the entire spectrum (though the sodium line 

 itself may be cut off) begins to affect the vision, and as the 

 increase advances ultimately extinguishes the rubidium lines 

 utterly. The degree of increase in brilliance when the lines 

 are at a maximum was determined by diluting the test-solu- 

 tion until a coil-full gave a line equally brilliant with that of 

 the standard. 



