131 
mass action. A proper equilibrium-constant is therefore not to be 
expected. 
The only exact datum concerning the composition of the alumi- 
nates is the melting-diagram of the system: CaQ—AI,O, determined 
by Snurprerp and Rankin‘). From this diagram there proved to be 
four compounds between these components. 
The modifications in which alummiumhydroaide may occur. 
In a similar way as described in the preceding paper, I tried 
to determine the solubility-curves (p and 7 constant) in this system. 
Also here the determinations were executed at 30,0° C. The NaOH 
used had been prepared from sodium, the water had been distilled 
and boiled immediately before use. The aluminiumhydroxide was 
prepared in various ways, for it is known that according to the 
preparation this compound shows different properties. The products 
used had been prepared as follows: 
A. Aluminiumhydrowide. 
Product a was obtained by precipitating an aluminium salt (sul- 
phate or chloride) with the required quantity of ammonia. The very 
voluminous, gelatinous precipitate was consequently sucked out and 
completely washed out, which took a long time. The gellous mass 
obtained in this way was dried at 1300—140°; after that it made 
the impression of a shrivelled up gellous mass and was very hard 
and glassy. Such a product does not possess a constant composition, 
the water-percentage varies according to the duration of heating. 
In the case of the product used, the time of heating had been chosen 
in such a way that the composition agreed as much as possible 
with Al(OH),. The water-percentage amounted to: 33,81 °/, (theore- 
tically for AKOH), to....34,57°/,). The particles of this product 
display no or hardly any perceptible swelling even after having 
been shaken a long time with distilled water. If however they are 
in contact with NaOH-solutions stronger than + 2 normal, they 
again swell very rapidly into a very voluminous product. This 
phenomenon renders the reaching of equilibrium particularly difficult : 
the swollen particles settle down very slowly. 
Product 8. In quite a different state aluminiumhydroxide can be 
obtained by issuing from the solution of an aluminate. If we gradu- 
ally decrease the alkalinity by carefully adding a diluted, weak 
acid (introducing CO, e.g.), then the hydroxide precipitates in a very 
compact, crystalline-looking form. Indications for the existence of 
1) Zeitschr. f. anorg. Chem. 68, 370 (1910). 
gx 
