294 F. W. Mar — Estimation of Barium as the Sulphate. 



supposed* that barium sulphate carrying alkaline salts may 

 be effectually purified, viz : by the solution of the washed pre- 

 cipitate in strong sulphuric acid and re precipitation by water. 

 Accordingly the determinations of the following series were 

 undertaken. The barium sulphate, precipitated from solutions 

 containing 5 grms of potassium chloride and 10 cm 3 of hydro- 

 chloric acid, was collected upon a filter, either paper or asbestos, 

 and, after burning the paper or removing the precipitate from 

 the asbestos (by tapping the crucible which held it and brush- 

 ing out with a camel's hair brush), was dissolved by warming 

 with concentrated sulphuric acid in a large porcelain crucible 

 and, after cooling, poured into water containing 15 cm 3 to 20 

 em 3 of hydrochloric acid. The water into which the solutions 

 in strong acid was poured was warmed with a view to diminish 

 the milkiness of the precipitate, but care must be taken to 

 keep the temperature below 60° 0. to avoid danger of spatter- 

 ing on the addition of the sulphuric acid. In the last two of 

 the experiments recorded a large amount of ammonium chlo- 

 ride was added to the water into which the solutions in acid 

 were poured, but this appears to have been without influence 

 upon the purification or the character of the precipitation. 

 The precipitates, after settling clear, were filtered upon asbestos, 

 ignited and weighed, the original felts being employed in those 

 cases in which asbestos was used in the first instance. Those 

 marked with an asterisk were gathered in the first filtration 

 upon paper, the paper being burned in the crucible in which 

 solution of the precipitate was subsequently effected. The re- 

 mainder were filtered originally upon asbestos. 





BaCl 2 . 2H 2 taken. 



BaS0 4 found. 



Error. 





(29) 



0-5026 grm. 



0-4746 grm. 



0*0044 grm 



. — 



(30) 



0-5035^" * 



0-4830 " 



0-0022 " 



+ 



(31) 



0*5016 " 



0-4767 " 



0-0024 " 



— 



(32) 



0-5025 " 



0-4804 " 



0-0050 " 



+ 



(33) 



0-5046 " * 



0-4829 " 



o-ooio " 



+ 



(34) 



0*5004 " 



0-4825 " 



0-0047 " 



+ 



These results show, evidently, that this process of purifica- 

 tion is not satisfactory. It is possible that the losses observed 

 may have been mechanical, and due to the violent action of, 

 the strong acid upon the water, but the excess in weight which 

 is noticed in the majority of the determinations can only be 

 attributed to residual contamination. 



Certain experiments, on the other hand, in which the solvent 

 action of sulphuric acid upon barium sulphate is utilized in a 

 different manner resulted more favorably. When a solution of 

 barium sulphate in sulphuric acid is evaporated to dryness, the 



* Fres. Quant. Anal., vol. i, p. 547. 



