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d. The system: water — Na,SO, — CuSO,. 
In this system three solid phases occur namely : CuSO,.5H,O, 
Na,SO, and a double salt Na,Cu(SO,), . 2H,O. 
The saturation line of the Na,SO, is represented by ab, that of 
the CuSO,.5H,O by cd and that of the double salt by be. Solution 
b is, therefore, saturated with Na,SO, and double salt, solution c 
with CuSO,.5H,0 and double salt. 
e. The quaternary system. 
In this system occur at 35° as solid phases: NaCl, Na,SO,, 
CuSO, .5H,O, CuCl, .2H,O and the double salt Na,Cu(SO,), . 2H,O. 
As the quaternary solutions saturated with a solid substance are 
represented by a surface in space (the saturation surface) we.have five 
saturation surfaces. Their projections are found in fig. 1. 
fg mne is the saturation surface of CuCl, .2H,O 
We a + ss NaCl 
ablk Re, Ms sy > NasO, 
Tee ee ES ke se CnS0 55.0 
GLEN Oe) >: 5 ¥ » Na,Cu(SO,),.2H,0 
In order to obtain a better view, there is indicated in the figure 
on each saturation surface the solid substance with which the solu- 
tions are saturated. By way of abbreviation we have represented 
