Ho 
was a possibility that under special circumstances, a erystallized 
hydroxide of a constant composition could be obtained. There are 
some intimations in the literature, that Zn(OH), sometimes seems 
to arise in a crystallized form. Thus Bercqurrer') states that he 
obtains the crystallized hydroxide by placing a zine bar wound 
round with a copper-wire in a solution of sicilie acid in caustic lye. 
In this process isometric octahedrons were formed, to which he 
ascribed the formula Zn{OH),. Various similar indications are found 
in the older literature though the observers do not agree as regards 
the composition of the crystals’). Of late years the zinchydroxides have 
been newly examined among others by Krein *). He distinguishes three 
forms of the hydroxide; form A is most strongly soluble in NaOH 
and arises by adding drop by drop ZnSO,-solution to a NaOH-solu- 
tion. The analysis of the product dried at a normal temperature 
yielded: 2Zn0.H,O. In course of time the forms B or C' separate 
out from the saturated solutions of A; both would have the com- 
position: ZnO.H,O, but B is sometimes obtained in fine crystals, 
whereas C is always amorphous. 
It is clear from the preceding that we need not demonstrate that 
a constant composition of the amorphous hydroxides is out of the 
question. The water-percentage of these substances depends on all 
kinds of factors: preparation, duration of keeping, ete.; hence a 
definite formula for them is valueless. 
The case is otherwise with the crystallized hydroxide. I really 
found it possible, to isolate the zinchydrovide as a crystallized phase 
of a constant composition. In doing so, [ set about it in the following 
manner: to 50 ¢.c. of a normal solution of KOH, I added a normal 
solution of zinc sulphate in drops from a burette. At the outset 
the hydroxide forming immediately dissolves, but finally a point 
is reached at which the liquid remains slightly turbid when 
shaken. On vigorous shaking and especially on scratching the 
glasswall and allowing to stand for a few minutes a heavy, sandy 
precipitate arises. Grafting with ervstals already obtained, appeared 
greatly to accelerate the separation. On mieroscopic examination the 
product gives an altogether homogeneous impression and it appears 
to consist of very small, drawn-out bar-shaped crystals. They filtrate 
very easily and contrary to the amorphous product, the erystals can 
1) Lieb. Ann. 94, 358 (1855). 
4) Cf. among others BopEKeErR. Lieb. Ann. 94, 358 (1855); ViLLE, Comp. Rend. 
101, 375 (1885). 
3) Zeitschr. f. anorg. Chem. 74, 157 (1912). See also Woop, Journ. Chem. Soc. 
97, 886 (1910). ¥ 
13 
Proceedings Royal Acad. Amsterdam. Vol. XXII. 
