( 618 ) 
on this we take a piece OW =1, point W then represents the 
fourth component JV. The different phases occurring in the system 
will then be represented by the points within the prism JV. AB. AC. 
CD. BD. 
As in the system now investigated the relation 
Cu SO, + 2 NH, Cl = (NH,), SO, + Cu Cl, 
takes place between the four salts we will, in the case of ammo- 
nium chloride, take the double molecule (NH, CD, and not the single 
one. If we proceed along the circumference of the square in a 
constant direction the angles represent successively the components: 
CuSO,, CuCl,, (NH,Cl), and (NH,),SO, the water will then be indicated 
by point W in space. 
We may now project the different points in space on an arbitrary 
plane; for this we choose a projection on the square and then obtain 
something like what is represented in Fig. 2. As the drawing would 
become too large the diagonals have only been drawn as far as 
necessary; the sides and angles of the square have been omitted. 
We will now consider first the different ternary systems. 
‘1. The system: water, CuSO,, (NH,),SO,. 
In this system investigated by Miss W. C. pr Baar three solid 
substances occur at 30° in equilibrium with the liquid, namely, 
(NH,)80,, Ca'50;.. 5 HO and CuSO, (NH), SO, „GHO: 
The isotherm theretore consists of three saturation lines, namely : 
=O cle EBD 
Ashe i An 
