20 



THE ANALYSIS OF POTASSIC CHLORIDE. 



same way. 1 Hence the use of a ground-glass plate 2 as a standard of 

 comparison is a very questionable proceeding. It appears that the precipi- 

 tation of argentic chloride from solutions of this salt differ perceptibly 

 in mechanism from the precipitation of the same substance from other 

 chloride solutions, even when argentic nitrate in great excess is used 

 in each case. 3 Accordingly, in order to secure a perfectly satisfactory 

 comparison, both precipitates must be dissolved in ammonia and repre- 

 cipitated. The precipitate then appears in each case in precisely the same 

 condition, and yields trustworthy results. 



The present tests were carried out in the following manner: Two 

 test-tubes of precisely the same volume (0.025 liter) were provided. Into 

 one of these was placed 0.015 liter of the wash-water, and into the other, 

 serving as the standard of comparison, a like volume of water containing 

 about as much carefully measured chlorine (in the form of potassic 

 chloride) as was present in the first. Into each was now run 5 ml. of a 

 three-hundredth normal solution of argentic nitrate. The solutions were 

 stirred with a platinum stirrer, previously cleansed with ammonia and the 

 purest water. After five minutes the precipitates were well formed ; they 

 were then both dissolved with the help of a milliliter of freshly distilled 

 ammonia, and reprecipitated with a slight excess of nitric acid, being filled 

 to similar marks near the top of the tubes. The two cloudy solutions, 

 thoroughly stirred, were allowed to stand and compared optically in the 

 nephelometer in the usual way. 



The following table compares the results obtained by the two methods. 

 The varying solubility of the halicle in the wash-water was mainly due to 

 difference in temperature at the time of the ablution. 



The Comparison of Weights of Argentic Chloride found Ncphelomctrically and 



by Evaporation. 



'Am. Chem. Journ., 31, 242 (1904); 35, 509 (1906). 

 2 Wells, Am. Chem. Journ., 35, 99 (1906). 



s Richarcls and Wells, Carnegie Inst. Pub. 28 (1905) ; Journ. Am. Chem. Soc., 

 27, 485 (1905). 



