A REVISION OF THE ATOMIC WEIGHT OF POTASSIUM. 



THE ANALYSIS OF POTASSIC CHLORIDE. 



INTRODUCTION. 



The atomic weight of potassium is a chemical constant of unusual inter- 

 est and significance. Standing, as it does, in the middle of the series of 

 five atomic weights of the most electro-positive metals -- substances 

 which exhibit in a highly marked degree both similarity and progressive 

 change in properties - - this number must be of unusual importance in the 

 search for that undiscovered mathematical relationship which undoubtedly 

 exists between these constants. Moreover, the atomic weight of potassium 

 is essentially bound up with the atomic weights of oxygen, chlorine, and 

 silver, this group forming a fundamental basis in the calculation of nearly 

 all the other atomic weights ; so that a change in the atomic weight of 

 potassium has a widely ramified effect on the whole table of atomic 

 weights. If any further evidence of this fact were needed, the recent 

 paper of R. W. Gray 1 would furnish it. 



The recent investigation upon the atomic weight of sodium by one of 

 us in conjunction with Dr. R. C. Wells 2 showed conclusively that Stas's 

 work, upon which rested earlier knowledge, was somewhat at fault in 

 several respects. The most serious of these errors were, first, the existence 

 of impurity in Stas's silver ; secondly, the fact that in his work solid salt 

 was dropped into the argentic solution, causing occlusion of salt ; and 

 thirdly, inadequate knowledge concerning solutions of argentic chloride. 

 In view of these errors it seemed not impossible that a similar revision of 

 potassium might likewise yield slightly lower results for potassium than 

 had been found by this master of exact analysis. For this reason the 

 present investigation was undertaken. 



Before describing the present work a brief historical review of previous 

 investigations may not be out of place. The determinations may be 

 divided into two groups the first group including all of these deter- 

 minations in which the molecular weight of a potassic halide was found 

 by decomposition of a chlorate, bromate, or iodate, and the second group, 

 those in which data for determination of the relation of potassium to 



!R. W. Gray, Journ. Chem. Soc. (Lond.), Trans., 89, 1175 (1906). 

 2 Richards and Wells, Carnegie Inst. of Washington Publication 28; Journ. Am. 

 Chem. Soc., 27, 459 (1905); Zeits. anorg. Chem., 47, 56 (1905). 



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