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DDM MAR 
1. The solubility-isotherm in the system Na,O-ZnO-H,O was com- 
pletely determined at 30°. 
2. We found that the following substances appeared as stable, 
solid phases: zinc-oxide ZnO, zincate of sodium Na,O-ZnO-4H,0, the 
monohydrate of sodium hydroxide NaOH-H,O. 
3. The sodium zincate forms very strongly incongruent solutions, 
by solutions below a concentration of 1 part of NaOH to 2 parts 
of water it is decomposed while separating out ZnO. | 
4. The amorphous, gelatinous zinchydroxide must be considered as 
a phase of a varying water-percentage; it cannot possibly be cleaned 
of adsorbed ions. It is metastable as regards crystallized zinchydroxide. 
5, Under special circumstances zinchydroxide is obtainable as a 
crystalline phase of the constant composition Zn(OH),. 
6. This crystallized hydroxide is metastable at 30° as regards ZnO. 
The cost of these investigations has been partly defrayed by a 
subsidy from the Van ’r Horr Fund which was put at my disposal. 
I here beg to express my cordial thanks to the Board of Admini- 
stration of this Fund. 
Anorganic and Physical-chemical 
Laboratory of the Technical University. 
Delft, June 1919. 
13* 
