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



great strength is to make the precipitate rather more insoluble, 

 if anything, than it is in water. In this connection, it should 

 be remarked that experiments of Fresenius,* together with 

 somewhat similar experience gained by the writer in another 

 line of work not included in this account, point to the fact 

 that the presence of an excess of sulphuric acid is an important 

 condition of "this high degree of insolubility. The exact 

 amount of such excess has not been determined, but the 

 amount used in the foregoing experiments seems to be suffi- 

 cient. 



In the preceding experiments, barium chloride was used in 

 considerable quantity. The following determinations were 

 made to ascertain whether very much smaller quantities of 

 barium would come down as completely and as soon, or 

 whether it is necessary to let the precipitations stand longer 

 before filtration. In these experiments the barium salt was 

 measured from a standard solution, containing 200 milligrams 

 of the chloride to the liter. The amounts of hydrochloric 

 and sulphuric acids, 15 cm 3 and' 10 cm 3 respectively, and the 

 whole volume of the solution was the same as in the former 

 experiments. 













Time in minutes 









BaCl 2 . 



2H 2 



BaSO. 



t 



between precipi- 



_ 





taken. 



found 





tation and filtra- 



JilT*"** 















tion. 







(14) 



0-0030 



grra. 



0-0024 



grru. 



120 



0-0004 



grm.- 



(15) 



0-0050 



*~ a 



0-0046 



^~a 



150 



0-0002 



a mmm 



(16) 



0-0050 



a 



j 0-0023 

 ( 0-0043 



a 

 a 



5 



60 



0-0025 

 0-O005 



t( 



it 



(1*) 



(18) 



0-0050 



a 



0-0031 



tc 



5 



0-0016 



a 



0-0050 



a 



0-0040 



a 



10 



0-0007 



a 



(19) 



o-oioo 



a 



0-0078 



it 



10 



0-0017 



a 



(20) 



o-oioo 



u 



0-0085 



u 



15 



o-ooio 



it 



(21) 



o-oioo 



u 



0-0083 



a 



30 



0-0012 



a 



(22) 



u-oioo 



a 



0-0087 



u 



60 



0-0007 



a 



From these results it would appear that the precipitation, in 

 the presence of hydrochloric acid to the amount indicated, 

 does not take place so rapidly when the amount of the barium 

 salt is small, but that two or three hours are sufficient for 

 reasonably complete separation of the precipitate in any case. 



In all the experiments described above there was no attempt 

 at a gradual admixture of the reagents but they were measured 

 out and at once added to the solutions, the whole being well 

 stirred. From the results obtained, it appears to be established, 

 as regards the usual precautions in precipitating barium by 

 means of sulphuric acid, that, contrary to former usage, it is 



* Zeitschrift fur Anal. Chem., vol. ix, p. 62. 



