( 1174 ) 
still exists only in quaternary solutions; the isotherm then assumes 
a form as in fig. 3. 
6. The isotherm at 15°. 
The equilibria occurring at 15° are represented in fig. 3; this is 
at once distinguished from that at 25° (fig. 2) by the disappearance 
of the saturation surface Z, and because the saturation surfaces of 
CuSO,.5H,O and Na,SO,.10H,O are partly joined along the line 
tu. The equilibria in the ternary systems water—NaCl—CuCl, and 
water—CuSO,—-CuCl, still belong, at 15°, to the same type as at 
25° and 35°; these need not, therefore, be discussed any further. 
The equilibria in the two other ternary systems are however, at 
15°, different from what they are at 25° and 35°; we will, therefore, 
briefly discuss these first. 
a. The system water — Na,SO,— NaCl. 
At 15°, only Na,SO, . 10 H,O and NaCl occur as solid substances; the 
point 7 is, therefore, the solution saturated with Na,SO, . 10 H,O+-NaCl. 
The saturation line of the NaCl is represented by /r, that of the 
Na,SO, .10 H,O by ar. 
b. The system water — CuSO, — Na,SO,. 
Owing to the disappearance of the double salt Na,Cu (SO), . 2 H,O 
the isotherm consists only of the saturation line at of the Na,SO, . 10 H,O 
and of the saturation line dt of the CuSO,.5 H,O. Solution ¢ is 
saturated with both salts. 
c. The quaternary system. 
The following saturation surfaces are found: 
ferang the saturation surface of CuCl, . 2 H,O 
hgmsr _,, > Ps » NaCl 
GIST, we Re De zo iNeS0OsA 0E 
dtune „ 45 Ke .. (CnsG.o Hag 
usmn _,, A En … Na Guts0)) 20 
Further, we find the saturation lines : 
en the saturation line of CuCl, .2 H,O + CuSO, .5 H,O 
nm 5, Le sm CuCl». HO + Na,Cu (SO) 2030 
Mg » sn » » OuCl, .2,H,0 + NaCl 
