183 
belongs to those salts that form the so-called incongruent solutions. 
On adding water, these salts do not yield a simple solution, but 
one of the components, from which we can imagine the salt to be 
formed, separates on the addition of water. Many instances of this 
are already known. With the zineate of sodium this phenomenon 
is specially pronounced. Not only will the addition of water to the 
solid salt effect a separation of ZnO, hence a decomposition of the 
compound, but diluted solutions of NaOH will likewise produce the 
same effect. From the isotherm we may infer, that solutions below 
a concentration of 33,3 Gr. NaOH to 100 Gr. solution (hence 1 
part NaOH to 2 parts of water) will cause a separation of ZnO 
from the solid salt, i.e. the concentration of the NaOH-solution will 
have to be raised beyond this boundary in order to obtain pure 
zincate crystals. The inadequate attention paid to this circumstance 
is probably the cause of the manifold contradictions in the literature, 
hardly anywhere do we find the concentration of the solutions 
indicated, thus obtaining in many cases mixtures of zincate crystals 
and ZnO, the possibility for this being very great as appears from 
the situation of the solubility-eurves. In analysing these mixtures 
investigators attributed the incorrect composition of a compound to 
them. This occurred among others with the experiments of Comry 
and Lorie Jackson’), who prepared zineates by solving ZnO in a 
hot, concentrated NaOH-solution, they then added alcohol to the 
liquid and in this way obtained two products: one from the layer 
of water by shaking out so long with alcohol till crystals appeared 
and one from the alcoholic liquid. 
I have repeated this method and in doing so I started from 50 
Gr. of water, to which 50 Gr. NaOH was added. After introducing 
17 Gr. ZnO in small quantities at a time, the zincate crystallized 
out in an appreciable quantity. According to our diagram we are 
in the centre of the saturation-region of the zincate. With the 
necessary precautions the crystal agglomerate was sucked out without 
any access of air and carbonic acid, and was then dried on porous 
earthenware. Of course the remaining liquor could not be altogether 
removed in this way, but washing-out without simultaneous decom- 
position is impossible. The analysis of the crystals produced: 
NasOs 208: 2/1 Zn0:537.8°/, HO. 13240 
(Theoretically for Na,O . ZnO. 4H,O... Na,O...28,9 °/,, ZnO...37,6 °/,, 
H,0...33,5 °/,). On microscopic inspection the product appeared to 
be perfectly homogeneous, the crystals showed as long bars with a 
1) Loe. cit. c.f. also GmeLIN-KRAvut?’s Handbuch. 
