472 J. I. Phinney — Barium Sulphate in Analysis. 



chlorides of these elements bring about no contamination. 

 However, in the above series of precipitations the inclusion by 

 the sulphate of sodium chloride and potassium chloride (left on 

 ignition) was very marked, and accordingly four new precipi- 

 tations were made, two in the presence of 10 grm. of sodium 

 chloride, and two with an equal amount of potassium chloride 

 as the contaminating salt, in order to test the degree of purifi- 

 cation reached by Fresenius' process. The evaporation was 

 made over a steam bath and hot water was used in washing. 

 It was found an easy matter to remove the precipitates from 

 the felts after ignition by breaking up the caked mass with a 

 glass rod by a rotary motion and gently tapping the crucible. 

 After extraction the residue was thrown back upon the same 

 felt, ignited, and re-weighed with results as below : 



Bad, . 2H.,0 



taken. 

 0-5000 grm. 

 0-5003 " 



BaCl 2 . 2H. 2 



taken. 

 0-5033 grm. 



0-5017 " 



BaS0 4 + NaCl 

 found. 

 0'4955 grm. 

 0-4973 •' 



BaS0 4 + KC1 

 found. 

 0-5024 grm. 

 05071 " 



Impurity 

 before treatment. 

 0-0177 grm. • 

 00193 •« 



II. 



Impurity 

 before treatment. 

 0-0215 grm. 

 0-0277 •' 



Loss on 

 treatmeut. 

 00079 grm. 

 0-0100 " 



Loss on 

 treatment. 

 0-0131 grm. 



0-0189 •' 



Impurity 

 remaining. 

 0098 grm. 

 00093 " 



Impurity 

 remaining. 

 0-0084 grm. 

 0-0088 " 



Under the most favorable conditions an average of O0090 

 grm. of the total impurity in a half-gram of the impure sul- 

 phate remained untouched, and in one case a retreatment 

 diminished this amount by only 0*0004 grm. Slight precipi- 

 tates were recovered from the filtrates of II, the first weighing 

 0*0001 grm. and the second unweighable. 



We are forced, then, to the conclusion that alkaline chlorides 

 do contaminate barium sulphate thrown down in the presence 

 of an excess of sulphuric acid* and that the process of purify- 

 ing by hydrochloric acid does not purify. It would seem 

 therefore that the only good method for purification is either 

 to fuse, according to Fresenius, with sodium carbonate, ex- 

 tract and reprecipitate as sulphate, or to evaporate from solu 

 tion in concentrated sulphuric acid according to Mar.f 



In conclusion, the author desires to acknowledge the sugges- 

 tions and help of Prof. F. A. Gooch freely given throughout 

 these investigations. 



' See also this Journal, xli, 288. 



f Ibid. 



