470 J. /. Phinney — Barium Sulphate in Analysis. 



by 10 cm 3 of distilled water, in the third, with 100 cm 3 of a 

 three per cent solution of the acid — though Ripper raises the 

 further objection, that upon ignition the precipitate becomes 

 so firmly attached to the felt that it is nearly or quite impos- 

 sible to make a thorough treatment with acid. In experiments 

 (1) and (2) no attempt was made to pulverize the precipitates, 

 but in experiment (3), as also throughout Series III, on moist- 

 ening with a few drops of water the sulphate was easily and 

 completely disintegrated by a glass rod into finely divided 

 particles. This difference in treatment explains, at least in 

 part, the large difference in the results of the following table. 









Series II. 





Weight 





BaCl 2 -2H 2 



Time of 



BaS0 4 





Treatment 



after 





taken. 



ignition. 



found. 



Error. 



with acid. 



treatment 



. Loss. 



grm. 





grm. 



grm. 





grm. 



grm. 



(1) 0-5071 



\ 1.0 min. 

 j 20 " 



0-4848 



0-0003 + 



i 4-5 drops HCl 

 1 4-5 " HCl 



0-4845 

 0-4845 



0-0003 



o-oooo 



(2) 0-5022 



J 10 " 



\ 20 " 



04799 



C001 + 



f 4-5 " HCl 

 | 4-5 '• HCl 



0-4796 

 04793 



0-0003 

 0-0003 



(3) 0-5007 



\l" 



0-4783 



o-oooi- 



j 100 cm 3 



| 3 per cent HCl 



0-4751 



0-0032 



The filtrates in experiment (2) gave with an excess of sul- 

 phuric acid slight unweighable precipitates, but from the fil- 

 trate of experiment (3) 0*0030 grm. of the sulphate were 

 recovered. The disintegrated residue from experiment (2), 

 (04793 grm. BaS0 4 ), was next treated under precisely the 

 same conditions as in the last preceding experiment except 

 that in this solution there was present dilute sulphuric acid 

 amounting to five percent of the entire volume, an excess 

 sufficient to keep the barium in the form of sulphate.* In 

 this case there was no loss in weight nor did the filtrate 

 contain any barium. 



This work completely demonstrates not only that strong 

 hydrochloric acid has no effect upon the film of asbestos, but 

 also that barium sulphate when thrown upon it may be brought 

 to a constant weight either by itself or after treatment with 

 dilute acids, and incidentally that the requisite excess of sul- 

 phuric acid must be present to counteract the solvent effect of 

 the hydrochloric acid. That Ripper failed to secure constant 

 weights is probably due to unfamiliarity with the proper sort 

 of material to be used. 



In view of the facts thus far ascertained the next step was to 

 purify the sulphate, if possible, by the means already referred 

 to in the beginning of this paper. The contaminating salts 

 chosen were potassium chlorate and sodium chloride, as those 



*Fresenius, Zeit. f. anal. Chem., xxx, 455 



