J. I. Phinney — Barium Sulphate in Analysis. 471 



most likely to present a fair test of the efficacy of the process. 

 The following precipitations were made : 



BaCl 2 . 2H a 



BaS0 4 





Contaminating 



No. taken. 



found. 



Error. 



salt. 



grm. 



grm. 



grm. 



grm. 



1. 0-5008 



0-5009 



00224 + 



KCIO3, 3 



2. 0-5014 



0-4990 



0-0198 + 



KC10 3 , 3 



3. 0-5007 



0-4980 



0-0196 + 



NaCl, 10 



4. 5004 



0-5165 



0384 + 



NaCl, 20 



5. 0-5012 



0-4979 



0-0190 + 



KCIO3, 3 



By reference to the following table in which the records of 

 treatment of these precipitates are given in their numerical 

 order, it will be seen that the action of hydrochloric acid in 

 the presence of sulphuric acid is to remove only from 70 to 90 

 per cent of the total impurity, and that, while it is possible 

 by repeated treatments with dilute hydrochloric acid alone to 

 so reduce the weight that there may be little or no apparent 

 error on the original determination, the large percentage of sul- 

 phate dissolved at the same time condemns its use in accurate 

 analytical work. 











Series III. 









Acids 



used 



Duration 











in total vol. 



of 



Loss on 



Impurity- 



BaS0 4 reco 



vered by 



of 100 



em 3 . 



acid treatment. 



treatment. 



remaining. 



H 2 S0 4 in 



filtrate. 



HC1 



H 2 S0 4 













cm 3 



cm 3 





grm. 



grm. 







r 3 



5 



30 min. 



00175 



0-0049 



none 









5 



15 " 



0-0012 



0-0037 



" 





- 



•.> 



5 



15 " 



0-0012 



0-0025 



unweighable trace 



g 



5 



15 " 



00000 



00025 



a 



u 





3 



5 



15 " 



0-0003 



0-0022 



u 



" 





I 3 







15 " 



0-0031 



0-0009 — 



00020 



grm. 



L 3 



5 



20 " 



0-0135 



0-0063 



none 





1 3 



5 



20 " 



0-0015 



0-0048 



" 





1 3 



5 



20 " 



0-0003 



0-0045 



" 





f" 3 



5 



30 " 



0-0090 



0-0106 



none 





1 ^ 



10 



20 " 



0-0013 



0-0093 



''.' 





< 10 



10 



20 " 



0-0023 



00070 



a 





| 25 



10 



20 " 



0-0002 



0-0068 



it 





^ 50 



10 



15 " 



0-0002 



0-0066 



u 





( 90 

 I 90 



10 



15 " 



0-0260 



00124 



none 





10 



15 " 



0-0009 



0-0115 



u 





j 3 







30 " 



0-0146 



0-0044 



0-0007 



grm. 





3 







30 " 



0-0040 



0-0004 



0-0032 



" 



Fresenius states' 55 " that barium sulphate impure from sodium 

 or potassium chlorates may be completely purified by igniting 

 the precipitate, moistening thoroughly with hydrochloric acid, 

 evaporating to dryness and extracting with water, and that 



* Zeit. f. anal. Chem., ix, 62. 



