LUEDEKIXG — ANALYSIS OF THE BARIUM GKOUP. 475 



ist. The presence of Calcium and Strontium salts are prejudi- 

 cial to the Ca SO^ test for Barium. 



2d. The presence of Calcium affects even in a greater degree 

 the delicacy of the Ca SO4 test for Strontium. 



In the light of these facts we are bound to seek for a more ex- 

 act method of analysis. From these same experiments such a 

 method, I believe, has been suggested. 



This method rests, in the first place, upon the fact, that, even 

 in the presence of large quantities of Calcium and Strontium, 

 Potassium Chromate will precipitate Barium on boiling if the 

 solution has been acidified with Acetic Acid. Eveh small traces 

 of Barium give this reaction, and there is no danger of confusing 

 it with either Calcium or Strontium. 



In all cases saturated solutions of K^ CrO^, or of K, Cr„0^, 

 must be used. 



After the separation of the previous groups, precipitate the 

 Barium group with (NH4)^C03, heat to boiling and filter ; 

 wash carefully the precipitate and dissolve in the least possible 

 quantity of Acetic Acid. Add to this solution an excess of satu- 

 rated K3 CrOj^. Heat for several minutes to boiling. If there is 

 a turbidity or precipitate, the presence of Barium is proven. Pre- 

 cipitate by this means all the Barium ; filter. Make the filtrate 

 alkaline with Ammonia and add (NH4)2''C03 in excess. A pre- 

 cipitate formed may be Strontium or Calcium, or Strontium and 

 Calcium. It is filtered, washed, dissolved in the smallest possi- 

 ble quantity of H CI, and tested for Strontium by means of the 

 spectroscope. Then H^ So^ is added to the solution, heated, the 

 precipitate filtered oft', and in the filtrate Calcium is tested for in 

 the ordinary way by means of Ammonium Oxalate. 



This method is capable of quick execution and certain in its 

 results, which is not the case with the old method. 



One other circumstance is to be noticed, i.e. large quantities 

 of Barium and Strontium do not hinder the detection of small 

 quantities of Calcium. 



Now this modified method has the disadvantage that for its 

 execution it is necessary to use the spectroscope, and consequent- 

 ly it is impossible to judge as certainly concerning the quantity 

 of Strontium present as in case of a precipitate test. The author 

 sought in vain for a long time to discover such a method. 



