( 139 ) 



Cu, Li, NH 4 and W indicate the four components Cu S0 4 , Li a S0 4 , 

 (NH 4 ) a S0 4 and water ; the triangle Cu Li NH 4 is the side plane on 

 which all is projected. The dotted lines Cu W, Li W and NH 4 W 

 are the projections of the rising sides of the tetrahedron and it is 

 obvious that the point W must lie in the centre of the triangle. 



The question is now what connection exists between the position 

 of a point in the tetrahedron and its projection on the triangle 

 CuLiNH 4 . 



Let us take a phase with the composition : Cu proportions of 

 Cu S0 4 , Li proportions of Li a S0 4 , N proportions of (NH 4 ) a S0 4 and 

 W proportions of water. The projection of this point on the triangle 

 Cu Li NH 4 may then be taken as indicating a phase which only 

 contains the three components Cu S0 4 , Li a S0 4 and (NH 4 ), S0 4 . 



Let us call these proportions Cu', Li' and N'. It is now easily 

 demonstrated that 



WWW 



Cu' = Cu H Li' = Li + — N' = N + — 



^3 ^3 ^3 



so that if the composition of a phase is known its projection may 

 be readily represented in a drawing. 



The double salt Li 2 S0 4 . (NH 4 ) 2 S0 4 is represented in the figure 

 by Dli; it is obvious that it must be situated on the line Li NH 4 

 as it consists merely of the components Li a S0 4 and (NH 4 ) a S0 4 . The 

 double salt Cu S0 4 . (NrIJ 2 S0 4 . 6 H 2 O which contains three compo- 

 nents must lie on the side plane W Cu NH 4 and is represented by Dc u . 



Both copper and lithium sulphate occur as hydrates, namely 

 Cu S0 4 . 5 H 2 O and Li a S0 4 . H a O; they are represented in the figure 

 by Cu B and Lij ; of course Cu 6 must lie on the side Cu W and Li 

 on Li W. 



Let us first consider the three ternary equilibria. 



1. Copper sulphate — ammonium sulphate — toater. The equilibria 

 occurring in this system at 30° have been determined by Miss 

 W. C. de Baat; the results of this investigation are represented by 

 the saturation lines ah, hpy, and gc; ah indicates the solutions 

 saturated with Cu S0 4 . 5H a O; gc is the saturation line of solid 

 (NH 4 ) a S0 4 and hpg represents the solutions saturated with Cu S0 4 

 (NH 4 ) a S0 4 . 6 H a 0. As the line W D Cu intersects the saturation line 

 hpg, the double salt is soluble in water without decomposition; its 

 solubility is represented by p. 



2. Lithium sulphate — ammonium sulphate — water. The equilibria 

 occurring in this system at 3CP are represented by the saturation 

 lines b e,e qf and ƒ c; the first is the saturation line of Li a S0 4 . H s 0; 



