( 47' ) 



On the AiKiJijsix of tlic Pxirnim (n-oiip. 



By C. LUEDEKIXG. 



The method ordinarily used for examination of the Barium 

 group precipitate, as it is described in Fresenius' Qiialitative 

 Analysis, proved itself to be unsatisfactory on several occasions. 

 It occurred that Barium was mistaken for Strontium, and that it 

 was impossible to find the latter at all when these substances 

 were present in small quantities with large quantities of Calcium. 

 After having assured myself of this fact by special experimental 

 investigation, I came to the conclusion that the method is inca- 

 pable of giving exact results, and that it is possible to overlook 

 quite considerable quantities of Barium and Strontium in work- 

 ing according to it. The thought involuntarily forces itself upon 

 one, that, in view of this fact, it has, no doubt, ifrequently hap- 

 pened that in mineral analysis these two elements have been 

 overlooked when accompanying Calcium. 



For the purpose of more exactly determining the limits of deli- 

 cacy of the method, I prepared a series of mixtures containing 

 different relative quantities of Barium, Strontium and Calcium 

 chlorides, and examined them according to it. I here give my 

 results in brief. 



A solution containing 0.003 ,?'• °^ ^^ ^^2 "^ -^ ^•^- ^^ water, 

 to which I c.c. of saturated solution of Ca SO^ was added, gave 

 an undoubted reaction for Barium. 



A solution containing 0.003 gr. Ba CI., in 3 c.c. of water gave 

 no immediate precipitate on addition of i c.c. of Ca SO^ solu- 

 tion ; however, after some time, so that one would have declared 

 that Strontium was present. This is therefore to be regarded a 

 limit of the delicacy of the reaction for Barium, and accordingly 

 we may say, that, if there is less than . i % of Barium in the solu- 

 tion, it cannot be detected by the Ca SO^ test. 



At the same time, for the purpose of comparison, I examined 

 into the delicacy of the test for Barium by Chromate of Potas- 

 sium solution. It was found tliat o.ooi gr. of Ba Cl.>, dissolved 



