132 
this form are to be found with various investigators '); VAN BEMMELEN 
ascribes to this product the formula: Al,O,3H,O; later on it was 
once, more examined by Russ’). The latter arrives at the same for- 
mula and finds that the separation will take place the sooner and 
the more completely as the proportion Na,O: Al,O, in the solution 
more closely approaches the value: 1,24: 1. 
The most suitable preparation of this form of the hydroxide 
appeared to me the following. To a solution of 25 Grs. of NaOH 
in 110 em? of water, 13,5 Grs. of aluminium are added in small 
quantities at a time. When the reaction is finished, the solution 
is quickly filtered and after that left open to the air for some days. 
Soon already the hydroxide begins to precipitate and as under the 
continued influence of the CO, from the air the OH'-ions eoncen- 
tration decreases, the quantity of hydroxide gradually increases. 
finally the product is filtered and completely washed out; it displays 
absorption of tons in a much smaller degree than product a, so 
that the purifying is greatly facilitated. Russ mentions that his 
product, even at a 500 fold magnification, did not distinetly prove 
crystalline; nor was this the case with the product obtained by 
me. At a 600 fold magnification a distinet crystalline structure was 
not perceptible. Therefore the opinion of former investigators, that 
here we have a crystalline form of the hydroxide, is premature 
as yet. 
Analysis of the product, after drying at 110° to constant weight, 
yielded: 34,29°/, H,O.... 65,62 °/, Al,O,, corresponding with 
the composition: Al,O,. 3 H,O. Carbonic acid could not be indi- 
cated, so that the at first not improbable supposition, that perhaps 
basic carbonates of aluminium would have arisen, was not con- 
firmed. When strongly magnified, the product also made a perfectly 
homogeneous impression, even when brought into prolonged 
contact with water, the particles do not show any swelling and 
do not alter externally. To their behaviour with regard to NaOH 
solutions, we shall revert later on, when treating the equilibriums. 
We may still remark that the particles are finer, more sandy and 
more compact as we cause the separation of the hydroxide to take 
place more slowly and gradually. If, for instance, we suddenly 
') Bonsporrr. Pogg. Ann. 27, 275 (1834). 
Becqueret. Compt. rend. 67, 1061 (1868); 79, 82 (1874). 
Kraemer. Archif. pharm. [2], 79, 268 (1854). 
Van BEMMELEN. Rec. trav. chim. Pays-bas. 7, 75 (1888). 
*) Zeitschr. f. anorg. Chem. 41, 216 (1904). 
