538 



The points of intersection of the saturation surfaces represent tlie 

 quaternary solutions, which are saturated with three solid substances 

 consequently the quaternary saturationpoints. In each of these points 

 three quaternary saturationcurves come together. In the ternary 

 saturationpoints, which we already discussed previously, two ternary 

 and one quaternary saturationcurve come together. 



The quaternary saturationpoints are the following: 



p saturated w^ith K, SO, + KCl + D 

 q „ „ K,SO, + D,,,+ D 



/ „ „ Cu, +D,.,.,-fD 



m „ „ Cu^ -f Cu, + D 



n „ „ Cuj +Di.2., + D 



„ „ KCl +D,.,., + D 



As it is easy to see from fig. 1, in presence of solution can exist : 

 K, SO, by the side of: KCl or D or D^.^.^ 



but not by the side of; Cu^ or Cu^ or Dj.j.,, 

 KCl by the side of: K, SO, or D or D^.,.,. 



but not by the side of: Di-i-^ or Cu. or Cu^ 

 Dj.,., by the side of: KCl or D or Cu, 



but not by the side of: K, SO, or Dj.j.gOrCuj. 

 Cu, by the side of: Cu^ or D or D^.,.^ 



but not by the side of: KCl or K, SO, orDj.!.^ 

 Cuj by the side of: Cu, or D or Di-^.g 



but not by the side of: K, SO, or KCl or Dj.,., 

 Di-i-g by the side of: Cuj or D or K,SO, 



but not by the side of: KCl or Dj.,., or Cu, 

 D by the side of all other substances. 



Different conclusions can be made from the figure. Let us con- 

 sider the behaviour of the salt D with respect to water. 



When D is the salt D;,^ it is indicated in the spacial represent- 

 ation by the point of intersection W of the diagonals (fig. 1). When, 

 however, D is the salt Dx, which contains water, it is situated in 

 the spacial representation on the line, wliich unites the top of the 

 pyramid with the point of intersection of the diagonals. Let us 

 assume that D ^ Da and let us call T the top of the pyramid, so 

 that point T represents the water. As the line D^T does not inter- 

 sect the saturation-surface of D;i, Da is not soluble in water without 

 decomposition. The line D^T intersects, however, the saturation- 

 surface iklq of D,.j.g, so that the salt Da = Cu SO,. K, CI, = K, SO,. 

 Cu CI, is decomposed by water, while D^.^.g = Cu SO,. K, SO,. öH^O 

 is separated. From this we see that we can not wash out the sail 



