on the Precipitation of Barium as Sulphate. 



403 



metaphosphoric acid acts similarly, and Spiller* notes the 

 same general effect where alkaline citrates are present. Series 

 III shows the results obtained by precipitating definite portions 

 of the standard solution of barium nitrate in the presence of 

 stated amounts of the substances just mentioned. The total 

 volume in every case was 100 cm 3 , the amount of dilute sul- 

 phuric acid used 10 cm 3 , and the time between precipitation 

 and filtration twelve hours. Upon filtering, igniting and 

 weighing the barium sulphate an excess of weight, due un- 

 doubtedly to contamination of the precipitate, was found. It 

 became necessary, therefore, to purify the precipitate as first 

 weighed in order to determine whether all the barium was 

 actually precipitated or whether a partial loss was covered by 

 the amount of included impurity. The method of purification 

 employed was that successfully applied by Dr. Marin the work 

 previously mentioned. The contaminated sulphate, collected 

 on paper and treated according to the familiar method (on 

 account of the difficulty attending the complete removal of the 

 precipitate from asbestos for purposes of purification), was dis- 

 solved in warm concentrated sulphuric acid, and evaporated 

 quickly and without spattering by means of the Hempel 

 burner, the barium sulphate being left after this treatment in 

 coarse granular crystals. The crystallized sulphate was warmed 

 with a little water containing a drop of sulphuric acid, filtered 

 upon an asbestos felt contained in a perforated platinum cru- 

 cible, the crucible and felt having been previously ignited and 

 weighed. 



Impurity present 

 to the amount of 

 5 grm. 



BaS0 4 equiva- 

 lent to Ba(SO s )o 

 taken. 



(1) Ammonium nitrate 

 (2) 



(3) " citrate 



(4) Sodium 



Series III. 



Apparent 



amount of 



BaSO, 



found. 



grm 



0-1800 



03440 



0-3442 



0-1730 



03511 



Error Percentage 



BaS0 4 after after of strong 



purifica- purifica- HX0 3 by 

 tion. tion. volume. 



grm. 

 0-1702 

 0-3410 

 0-3407 

 0-1366 

 03470 



grm. 

 0-0008- 

 0-0005 — 

 0-0005- 

 0-0006 + 

 0-0009 + 



10 



grm. 

 0-1710 

 0-3415 

 0-3412 

 0-1360 

 (5) Metaphosphoric acid 0*3461 



The results show that in the. presence of nitric acid amount- 

 ing to one tenth by volume of the entire liquid these salts 

 exert no apparent interference with the precipitation of the 

 barium. 



The entire work would seem to show that the presence of 

 an excess of nitric acid or aqua regia amounting to ten per 

 cent by volume of the liquid treated is not only not to be 

 avoided in estimating barium as the sulphate, but is actually 

 beneficial. Ordinarily the advantage is found in the tendency 



*Chem. News, viii, 280-281. 



