THE ANALYSIS OF POTASSIC CHLORIDE. 



All weighings, whether of this salt or of silver or argentic chloride, 

 were made by substitution in the manner already described in other 

 papers. 1 The balance was a short-armed instrument made by Troemner, 

 of the type adopted in other similar investigations ; it was used only for 

 this work and that to be described afterward. The weights were of 

 platinized brass, carefully standardized according to the usual Harvard 

 method. 2 



All weighings were reduced to the vacuum standard. Thus from every 

 apparent gram of silver, 0.00003 gram was subtracted, and to every 

 apparent gram of argentic chloride, 0.000071 was added, if the tempera- 

 ture was 20 and the pressure normal. Assuming the density of potassic 

 chloride to be 1.995, the similar correction for this salt .was -f- 0.00045G. 

 Changes in temperature and pressure occasionally caused slight but 

 usually inessential changes in these corrections. 3 



The wholly colorless, transparent, fused salt was dissolved in the purest 

 water in a covered beaker of Jena glass under a tightly fitting bell- jar. 

 The solution was always perfectly clear, except in the rejected case already 

 cited and one other similar one. After this solution had been very thor- 

 oughly washed away and used for analysis, the platinum weighing bottle 

 was heated for a short time in another crucible, and weighed in prepara- 

 tion for another analysis. The constancy of these weighings has already 

 been discussed. 



The details of preparation having been described, the analytical methods 

 themselves must be indicated. The problem was, as in the case of sodium, 

 to determine the amount of chlorine present, the weight of potassium 

 being found by difference. Both of the previously used methods for 

 finding the amount of chlorine were used, and the details are so much 

 like those discussed by Richards and Wells 4 that much may be assumed 

 as understood. For a full understanding of the present work, that upon 

 sodium should be read in connection with it. 



The two methods for the determination of chlorine, namely, the weigh- 

 ing of the precipitated argentic chloride on the one hand, and the dis- 

 covery of the equivalent amount of silver on the other, are discussed 

 below in order. 



1 For example see Richards and Rogers, Zeit. anorg. Chem., 10, 19 (1895) ; also 

 Richards and Wells, Journ. Am. Chem. Soc., 27, 465 (1905). 



2 Richards, Journ. Am. Chem. Soc., 22, 144 (1900). These weights had an average 

 density of 8.3. 



3 Richards and Wells, Journ. Am. Chem. Soc., 27. 465 (1905). 



4 Loc. cit. 



