188 
be washed out very rapidly. On drying at 40°—50° the analysis 
yielded : 
18,06 °/, H,O; 81,91 °/, ZnO (Theoretically for Zn(OH),....18,11°/, H,O 
81589 „Za: 
The concentration of the KOH-solution was varied between the 
limits of 4,0 and 0,1 normal; the concentration of the zinc sulphate 
solution likewise; the crystals formed always were of the same 
shape and composition. 
Stability of crystallized zinc hydroxide towards zinc oxide. 
The experiments Nes 26—31 of Table 1 give an insight into the 
stability-relation of the crystallized Zn(OH), and ZnO. With No. 26 
the solid phase was added as crystallized Zn(OH),; the mass was 
kept for over a fortnight in the thermostat at 30°. It then appeared 
that the crystalline Zn(OH), had been entirely converted and 
the solid phase consisted of ZnO. This was confirmed by the ana- 
lysis of the solution and remainder, the point found falls on the curve 
AB. So it appears from this, that at 30° the erystallized zine hy- 
drozide is metastable towards ZnO. 
With a shorter equilibrium-adjustment 7 proved possible to deter- 
mine the metastable solubility curve of Zn (OH),. No. 27 was set 
in with erystallized Zn (OH), and after + 24 hours the solution 
was analysed; the solid phase appeared to consist even then of 
crystallized hydroxide. Conformable to this the zine percentage of 
the solution (c. f. table) was considerably higher than corresponds 
to the curve AB. Numbers 30 and 31 have been executed in a 
similar manner, here again crystallized Zn (OH), was added as a 
solid phase, the solution being analysed after + 24 hours. The 
determined compositions of the solution again lie considerably above 
curve 4B. The points representing these solutions form together the 
metastable solubility curve ZF of the crystallized zine hydroxide. 
Finally the determinations Nes 28 and 29 have been carried out 
in the same solution, to which erystals Zn(OH, were added as a 
solid phase. After about + 24 hours the solution yielded the com- 
position N°. 28, Zn(OH), being present as a solid phase. Whereas 
after one day these crystals still appeared to be present, the solution 
still being of the same composition, we found three weeks later on 
the composition N°. 29. All the Zn(OH), crystals had disappeared; 
the point now found lies on AB, while the analysis of the rest 
indicated too, that ZnO was present as a solid phase. Other circum- 
stances being equal the solubility of crystallized Zn(OH), is conside: 
rably higher than that of ZnO. 
