LUEDEKING — ANALYSIS OF THE BARIUM GROUP. 473 



We have, then, sufficient grounds for putting aside the old 

 method of analysis and substituting- the Chromate test. 



It must also be added that dilution appears to decrease the 

 effect of the Calcium, and therefore that tlie effect is proportional 

 to the concentration of the solution. But by dilution again the 

 test for small quantities of Barium is rendered impossible, so that 

 we are obliged to work with concentrated solutions. But even 

 in the most dilute solutions the K2 Cr., O- shows itself far supe- 

 rior to the Ca SOj^ test, as is shown by our experiment. 



In a similar way the delicacy of Ca SO^ as a reagent for Stron- 

 tium was tested. 



To a solution of 0.001 gr. vSr CI 2 in 2 c.c. water, i c.c. of Ca 

 SO4 solution was added and the mixture heated to boiling. There 

 was no immediate precipitate, as the Strontium reaction requires ; 

 but, after boiling ] of an hour, a very slight precipitate appeared. 



A solution of 0.003 gr. of Sr Ci^ in 3 c.c. water, to which i c.c. 

 Ca SOj^ solution was added, gave on boiling a very fine precipi- 

 tate, and one could conclude with perfect impartiality that Stron- 

 tium was present. 



These are therefore the limits of the Strontium reaction with 

 Ca SOj^ under the most favorable circumstances, and it is possi- 

 ble by that means to detect 0.06 c^ of Strontium in solution. We 

 conclude, also, that the Ca SO4 test is somewhat more delicate 

 for Strontium than for Barium. 



For the same reasons which we gave above in the case of Ba- 

 rium, it was necessary to ascertain the effect of the presence of 

 much Calcium upon the Ca SO^ test for Stronium. This influ- 

 ence — an item of great importance in practical analysis — was 

 proven to be far greater upon Strontium than upon Barium salts. 



As a matter of fact, the test by means of Ca SO4 is not in the 

 least delicate, and therefore is perfectly ready to be laid aside. 



To 0.030 gr. Sr CI 3 and 0.986 gr. Ca Clg, dissolved in 4 c.c. 

 water, i c.c. of Ca SO4 solution was added. There was no 

 precipitate even after boiling hard for ten minutes. To it was 

 then added i c.c. Ca So^ solution and 0.020 gr. SrCU dissolved 

 in 2 c.c. water. There was still no precipitate even after boiling 

 several minutes. There was added 0.120 gr. SrCl., dissolved in 

 12 c.c. water, and also i c.c. Ca SO4 : still no precipitate after 

 hard boiling. There was added in large quantities both SrCU 



