•127 



As, Os and the halogenide, oonseqnently without tlrst dissolving 

 As^Os ill a base. Therefore, we had to deal with equilibria in the 

 ternary systems : water-.-lx.^ ^>,-halogeiiide. 



Of course we have to bear in mind in judging the results, 

 that the possibility is never excluded that besides the compounds 

 which have shown themselves, others might exist, that even the 

 compounds foimd might be metastable. 



/>. The system : HJ) — Asjj, — KCl at 30°. 



In this system at 30° the two components As J), and K(Jl occur 

 as solid phases and further a compound, which we shall call D. 

 The composition of this compound is defined with the aid of the 

 rest-method, but is not known exactly. It is sure, however, that it 

 has not the composition; {As„LK}i i'^Cl; it is about [As^O,)^{KCl)r^ 

 or {As,0^)i,{KCl)^; we shall refer to this further. 



In fig. 1 in which the point Z indicates the component KC/ the 

 isotherm of 30° is represented schematically, this isotherm consists 

 of three branches; 



ah represents the solutions, saturated with As,0, 

 be „ „ „ „ „ D 



cd „ „ „ „ „ KCl. 



The composition of the solution l>, which is saturated with As^O, -\- D, 



has not been defined. It is apparent from table 1 that its percentage 



of KCl will be between 10,37 and 11.22 7o ^^^^ ^hat its percentage 



of As^O^ will be somewhat higher than 2.46 7o- Further it is 



apparent from table 1 that the solubility of AsJ)^ with increasing 



percentage of KCl of the solution increases a little, viz. from 2.26°/„ 



to a little over 2.46 7n ; consequently the point b is situated somewhat 



further from the side IF^Z than the point 

 if 

 •^^ ^ a. Further it is apparent from table 1 



that the solubility of the compound D 

 decreases at increasing percentage of 

 KCl of the solutions, viz. of over 

 2.467„ to about 0.787„ (in table 1 the 

 average of N". 12 and 13); curve Ac ap- 

 proaches, the side WZm fig. 1 therefore 

 from b. Consequently we see that the 

 Pig y. solubility of As^O^ increases at first a 



little by adding KCl, until the compound Z) is separated, after which 

 the solubility decreases, [from 2.267» in pure water (point r?) towards 

 0.78 7o if' a solution saturated with KCl (point c)j. 



