472 TRAXS. ST. LOUIS ACAD. SCIENCE. 



in 3 c.c. of water, still gave a perceptible precipitate on addition 

 of one drop of a saturated solution of Chromate of Potassium. 



We conclude, therefore, that the reaction for Barium with Po- 

 tassium Chromate is more delicate than with Ca vSO^, since by 

 the Chromate test we can detect Earium if there is only .03% in 

 solution. According- to the usual method of the analysis of the 

 Barium Group the (NHj^)2 COg precipitate is to be dissolved in 

 H CI, then evaporated to dryness in order to expel any excess of 

 H CI. The residue is now dissolved in the least possible amount 

 of H., O, and a portion tested with Ca SO^. We must, therefore, 

 show the delicacy of the Ca SOj^ test under other conditions also, 

 that is, in the presence of an excess of Strontium and Calcium. 



The following are the results of the experiments made for 

 this end : 



To 0.020 gr. Ba Ci._, and 0.9S6 gr. CaCl,,, dissolved in 4 c.c- 

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

 precipitate. 



To 0.003 gr. ^^''^Clo and 0.986 gr. Ca CL,, dissolved in 2 c.c. of 

 water, 3 c.c. of solution of Sodium Acetate with 2 c.c. of a satu- 

 turated solution of Potassium Bichromate were added. In the 

 cold there was no precipitate ; after boiling, one appeared. Sodi- 

 um Acetate and Potassium Bichromate were used in order to 

 make the solution strongly acid with Acetic Acid. 



To o.oio gr. Ba Cl., and 0-986 gr. Ca CU, dissolved in 13 c c. 

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

 cipitate., which was however the case on the addition of a solu- 

 tion of Bichromate of Potassium. 



These experiments show with sufficient clearness that the reac- 

 tion of Barium with K^CrgO; is more delicate than with Ca SO^^ 

 under similaf conditions. It' also appears that the presence of 

 the large access of Calcium retards the Ca SOg to such a degree 

 that it can no longer be called delicate. 



In our experiments we used of Barium Chloride only -^i^ as much 

 as of Calcium Chloride, or about 2fc of it. Further, we see that 

 by the conditions of the experiment 0.02% Ba CL, may be over- 

 looked in the course of the usual analytical method. 



We see, too, that the K2 Cr^ O- test is not only more delicate 

 in general, but, what is more important, it is influenced in a much 

 less degree by the presence of an excess of Calcium. 



