A REVISION OF THE ATOMIC WEIGHT OF MANGANESE. 



47 



The final averages of the four series are given in the following table: 



Series 



I. 



II. 



III. 



IV. 



MnBr2: 2Ag 54-934 



MnBr2: aAgBr S4-930 



MnCU: 2Ag 54-933 



MnCU: 2AgCl 54-933 



Average, 54-933 



It is interesting to tabulate the analyses according to the specimens of mate- 

 rial employed. 



The purification of Sample B was exceptionally thorough. In the first place 

 potassium permanganate is isomorphous with a comparatively limited number 

 of substances, so that the initial purification by a large number of crystallizations 

 of this substance may be expected to have eliminated every trace of impurity 

 of heavy metals. In the second place the final product had been many times 

 recrystalUzed in the form of two other compounds of manganese. It is almost 

 inconceivable that any impurity could have eluded this large number of crys- 

 tallizations in three different forms. That such a prolonged purification was 

 unnecessary is shown by the agreement of the results from the other samples 

 with that from Sample B. Even in the case of Samples A, C, D, and E the 

 final product had been recrystallized in at least two forms. The slightly lower 

 results in the case of Sample D differ from the others by an amount no greater 

 than the possible experimental error, and can not be considered to indicate that 

 the composition of this sample is different from that of the others. The vari- 

 ous samples of silver also yielded essentially the same result, which confirms 

 the statement as to the identity of the different samples made on page 37. 



There can be little doubt that the final average of all four series, 54.933, repre- 

 sents with accuracy the relation of the atomic weight of manganese to that of 

 silver 107.880. This value is in close agreement with the value derived from 

 previous investigations. 



The main results of this research may be briefly summarized as follows: 



(i) The atomic weight of manganese, referred to silver 107.880, is found to 

 be 54.933, by analysis of both manganous bromide and manganous chloride. 

 With silver at 107.870, manganese becomes 54.927. 



(2) The specific gravity of manganous bromide at 25°, referred to water at 

 4°, is found to be 4.385, and that of manganous chloride under the same con- 

 ditions is found to be 2.977. 



Analysis 30 is rejected. 



