RICHARDS AND PARKER. — BARIC SULPHATE. 67 



II. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



ON THE OCCLUSION OF BARIC CHLORIDE BY 

 BARIC SULPHATE. 



By Theodore William Richards and Harry George Parker. 



Presented January 9, 1894. 



It has been knowu for a long time that baric sulphate possesses the 

 power of carrying dowu other substances with it during the process of 

 precipitation. Many experimenters have investigated with more or less 

 accuracy the conditions which determine the amount of the occlusion 

 in different cases, and have sought to eliminate as much as possible 

 the error which the occlusion must introduce into analytical results.* 

 Long ago, Fresenius found that some of the imprisoned salts, which 

 could not be set free by any amount of washing of the freshly pre- 

 pared baric sulphate, might be partially dissolved by water or acid 

 after the precipitate had been ignited. Recently J. J. Phinney t has 

 shown that in some cases, perhaps in all, this purifying process is, 

 only partial ; hence it becomes important to discover a new method 

 ■which may yield more satisfactory results. As Fresenius pointed out 

 long ago, I the dissolving of the sulphate in sulphuric acid does not 

 answer when barium salts are occluded. 



The occlusion of baric chloride, the salt which is most generally 

 used as the precipitant of sulphuric acid, has long been recognized. 

 In most text-books upon quantitative analysis one is directed to pour 

 the baric chloride into the sulphuric acid, and not vice versa ; and it is 

 generally understood that this precaution is in order to prevent as 



* A partial bibliography of the subject is given by M. Ripper, Zeitschr. fiir 

 Anorg. Chem., II. 36. See also Jannasch and Richards, Journ. f. prakt. Chemie, 

 [Neue Folge,] XXXIX. 321, XL. 236 ; E. A. Schneider, Zeitschr. fiir Physikal. 

 Chem., 1892, X. 425 ; Lunge, Journ. f . prakt. Chemie, XL. 239 ; F. W. Mar, Am. J. 

 Sci., [3.], XLL 288 ; P. E. Browning, Am. J. Sci., [3.], XLV. 399 ; J. J. Phinney, 

 Am. J. Sci., [3.], XLV. 468; Richards, These Proceedings, XXVI. 258 ; XXIX. 

 67, etc. 



t Am. J. Sci., [3.], XLV. 468. t Zeitschr. Anal. Chem., IX. 52. 



