RICHARDS. — ATOMIC WEIGHT OF BARIUM. 67 



to add a very slight excess of silver, to warm, agitate, and filter the 

 solution, and to determine the excess in the filtrate by means of an 

 equivalent solution of ammonic sulpho-cyanate, after the method 

 of Volhard. Sanger* has pointed out that the solubility of argentic 

 chloride seriously affects the accuracy of this method unless the 

 argentic chloride is filtered off before the addition of the sulpho- 

 cyanate ; and the experience of this Laboratory had independently 

 led to the same conclusion. It is to be hoped that Clemens Winkler 

 observed this precaution in his interesting analyses of cobaltous 

 and nickellous chloride ; f if not, the atomic weights obtained are 

 probably too high. 



The three equivalent solutions of argentic nitrate, hydrochloric 

 acid, and ammonic sulphocyanate each corresponded exactly to a 

 milligram of silver for each cubic centimeter. These solutions are 

 referred to whenever a standard solution is mentioned below. 



It is needless to say that the measuring apparatus was all calibrated 

 with great care ; moreover, for the final experiments the solutions 

 were weighed in small flasks provided with tightly fitting graduated 

 pipettes, as well as measured. This last precaution was hardly neces- 

 sary, however. Of course, the ordinary methods of volumetric analysis 

 are not applicable to the determination of atomic weights ; but when 

 the greater part of a reagent has been weighed out, the last few milli- 

 grams may be added by the measurement of a very dilute solution with 

 an accuracy quite equal to that obtainable upon a balance. $ 



Ratio of Baric Chloride to Baric Sulphate. 



It is well known that such a ratio as that of baric chloride to baric 

 sulphate could form at best but a very poor basis for determining the 

 atomic weight of barium. § An experimental error in the process 

 is necessarily magnified many times when referred to the constant 

 sought. Nevertheless, since five distinguished chemists have tried 

 this method, it was thought expedient to attempt it, in order to show 

 if possible the cause of the great discrepancies in their results. 



The investigation of the ratio occupied several months, but the re- 

 port of it will be greatly abbreviated. The principal cause of error was 



* These Proceedings, XXVI. 34. 

 t Zeitschr, Anorg. Chem., IV. 10. 



t This point, among others, seems to have been misunderstood by G. Hin- 

 richs, of the College of Pharmacy, St. Louis. (Chem. News. LXVTII. 171.) 

 § Ostvvald, Allgemeine Chemie, I. 23. These Proceedings, XXVIII. 11. 



