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For the first mentioned three-phase lines 
Three-phase line Three-phase line 
Na 3 S0 4 10 aq. + L + G 
Na 3 SQ 4 + L + G 
32.8 
33.8 
35.0 
37.0 
vas found: 
Three-phase line 
Na*SO 4 10aq -f Na,S0 4 -f G 
in which P, and P, are two three-phase pressures at the absolute 
temperatures T„ T„ P„ and P, denoting the vapour tensio 
pure water at the same temperatures. ,,, 
Q indicates then the heat-effect in the formation of decahydrate 
from 1 gr. mol. of liquid water and anhydride. 
If we take the pressures corresponding with 20 and 32 4 we 
find for Q = 2440 cal., from which follows that the total heat o 
hydration of Na, S0 4 .10 H,0 = 24400 cal. . 
We may mention here at the same time that this indirect dete - 
