"CHROMATE METHOD" FOR SEPARATING EARTHS VICKERY. 31 



carbonates were then dissolved in the least possible quantity 

 of acetic acid, the solution diluted, barium removed as 

 chromate, and ammonium sulphate added to the filtrate. 

 This was supposed to throw down the insoluble strontium 

 sulphate, but retain the calcium by its solvent action upon 

 calcium sulphate. 



It was at this point that difficulty was usually encountered 

 as the calcium almost invariably came down in some quantity, 

 especially if present in large amounts, rendering a complete 

 separation impossible and obscuring the confirmatory flame 

 tests. However, sufficient calcium was retained to give the 

 confirmatory oxalate test, and by again bringing the precipi- 

 tate into solution and treating with a solution of calcium 

 sulphate, the strontium was confirmed even in the presence 

 of a large amount of calcium. This method, resulting as 

 it does in only an approximate separation, is unsatisfactory, 

 and attempts were made to improve it. 



Solutions of barium, strontium and calcium as chlorides 

 were made up and carefully standardized gravimetrically, 

 the first two by precipitating a known volume with silver 

 nitrate, and the last with ammonium oxalate. Appropriate 

 volumes of these solutions were run from burettes into flasks 

 and made up so that each solution should contain a milligram 

 of the metal per cubic centimeter. These standard solutions 

 were used for the analysis. 



The first step was to investigate quantitatively each 

 precipitation occuring throughout the procedure and record 

 its delicacy under the conditions normally occuring in the 

 course of an analysis. The method followed was to run 

 various quantities of the standard solutions into a series of 

 beakers, dilute them with hot water, and add the cold reagents 

 in the order given. This resulted in the precipitation taking 

 place at a temperature of 65°-70°. By watching the row of 

 beakers it was easy to compare the amounts of precipitate 

 occurring and to find that one which yielded no precipitate. 



