74 PEOCEEDINGS OF THE AMERICAN ACADEMY. 



milligrams per litre ; and in a third, much less violently shaken, but 

 allowed to stand for a week, it was as much as 2.7 milligrams per litre. 

 In each of these cases the temperature was about 20°. 



These results are, as one would expect, between the limits set by 

 Stas ; for the precipitate was in the state usually observed, having 

 lost its first flocculence, and not having been wholly converted into 

 powder. 



A careful series of experiments was made to confirm Stas's state- 

 ment that the chloride is absolutely insoluble in water containing an 

 excess of argentic nitrate. It is not needful further to describe these 

 experiments, except to state that the confirmation was wholly satis- 

 factory. In the course of this work I was able to detect repeatedly 

 one part of chlorine in thirty million parts of water, by careful com- 

 parison in strong sunlight after treatment with excess of argentic 

 nitrate. The very faint opalescence of course very soon disappears, 

 owing to the blackening of argentic chloride by the powerful light. 



Ratio op the Chlorides of Silver and Barium. 



The properties of the two chlorides having been studied as far as 

 they are concerned in the present work, it was now possible to com- 

 pare their molecular weights. Very definite advice with regard to 

 the precautions necessary in such a comparison has been given by 

 Stas,* and most of his suggestions have been found of use. One 

 recommendation, however, although most useful for ordinary work, is 

 of questionable propriety when applied to the most precise work. In 

 order to prevent argentic chloride from being dissolved by the water 

 used for washing it, Stas advises the exclusive use of a very dilute 

 solution of argentic nitrate for the purpose.! I have found it very 

 difficult wholly to free argentic chloride' from traces of the nitrate, 

 even by long continued shaking with pure water, and of course this 

 difficulty is increased by the presence of additional impurity. The 

 small amount of argentic nitrate which is certain to be left behind, 

 according to the method of Stas, decomposes and blackens a little of 

 the chloride upon fusion, even in the dark ; and no suitable correc- 

 tion can be applied to counteract the error. Accordingly, pure water 

 was always used for the final washings during the present work. 



* Mem. de l'Acad. Belg., Vol. XLIII. Part II. p. 66. 



I Professor Cooke also suggested this method of procedure. (These Pro- 

 ceedings, XVII. 7.) 



