474 TRANS. ST. LOUIS ACAD. SCIE.VCE. 



and Ca SO4 and still it was impossible to get a precipitate even 

 after boiling a long time. 



These experiments need no comment. The influence of Cal- 

 cium salts in hindering the test for Strontium with Ca SO^ is 

 enormous, and it is possible to overlook large quantities of Stron- 

 tium in testing by the usual analytical method. 



In practice, the retarding influence of Strontium upon the Ba- 

 rium test is of minor importance ; but, to make the discussion 

 complete, I have examined this case also. In the presence of 

 much Sr Clo in solution it is not possible to distinguish as to the 

 absence or presence of small quantities of Barium. It appears 

 as though the Strontium reaction with Ca SO^ more and more 

 likens the Barium reaction in the measure of its concentration. 

 Thus a 30 </f Sr CI. 2 6-aq. solution gives with Ca SO^ an imme- 

 diate precipitate even in the cold ; thus giving an appearance 

 which should indicate the presence of Barium. 



With more diluted Strontium solutions we get a very different 

 result. In this case the influence of Strontium in solution is ex- 

 actly similar to the influence of Calcium considered above. 



For example, 2 c.c. of a Sr CU 6-aq. solution, with 0.003 §''• 

 Ba Clo in solution, gives, on the addition of i c.c. Ca SO 4, no 

 immediate precipitate ; so that it is impossible to detect small 

 quantities of Barium by this means. Indeed, the precipitation is 

 no quicker in this case than wath an equally concentrated Stron- 

 tium solution, under the very same conditions. 



Of a very different character is the reaction of a small quan- 

 tity of Barium in the presence of a large amount of Strontium, 

 with the reagent K, Cr^O-. 



2 c.c. of a 6-% SrClg 6-aq. solution, to which 0.002 gr. BaCl^ 

 had been added, was acidified with Acetic acid, and to that was 

 added a few drops of Sodium Acetate solution, and then Potas- 

 sium acid chromate. On heating, the solution became very dis- 

 tinctly turbid, and in the course of a few minutes a precipitate 

 of BaCr04 had deposited. A Strontium solution of the same 

 strength, under the same treatment, showed not the slightest 

 turbidity. These experiments indicate plainly the delicacy and 

 trustworthiness of the Potassium Chromate. 



By our experiments two facts have been proven : 



