141 
The equilibriums along AG; the sodiumaluminate: 4 Na,O. 
GALO,.16 1,0, 
When alumiumhydroxide is dissolved in ever more concentrated 
solutions of NaOH, the sodiumaluminate from the above-mentioned 
formula crystallizes; curve AG in fig. If represents the solubility- 
curve of this salt. The compound crystallizes very well in diamond- 
shaped crystals; the equilibriums are reached much more easily than 
the others. The composition of the aluminate has in the first place 
been deduced from the results of the rest analyses. In the second 
place the wet salt was sucked out without the access of air, dried 
without the removal of the adhering mother-lye and analysed 
afterwards. The result was: 30,1 °/, Na,O; 37,1 °/, Al,O, (theoretically 
for the composition above-mentioned: 29,5 °/, Na,O; 36,4 °/, Al,Q,). 
As the salt forms very strongly incongruent solutions, a complete 
removal of the mother-lye is practically impossible. Taking this into 
consideration, the composition found corresponds very satisfactorily 
with our formula. The solubility-curve AG has as stable ends: on 
the one side A, the triple-point: Al,O,.3H,O + 4Na,O.3 Al,O,. 
16H,O + solution; on the other side G the triple-point: 4 Na,O. 
3AI,0,. 16 H,O + 4Na,O. Al,O, . 10 H,O + solution. The metastable 
part ABC of the curve AG is partly determined; on this a series 
of metastable triple-points are situated, of which B and C, both 
indicating the coexistence of the aluminate with gelatinous hydroxide, 
are determined. 
The equilibriums along GH; the sodiwmaluminate 4 Na,O. 
MeO 10 HO. 
To AG is joined the curve GH relating to a second compound, 
an aluminate of the composition: 4 Na,0. Al,O,. 10 H,O. Like 
the former compound it is well crystallized in needle-shaped 
crystals, which are very hygroscopical. Isolation of the pure salt 
yielded the same difficalties as have been described with the other 
aluminate. This too was sucked out with all precautions and quickly 
dried on porous earthenware. Analysis of the product thus obtained 
yielded: 47,6°/, Na,O; 18,1 °/, Al,O, (theoretically for the above- 
mentioned composition 46,8°/, Na,O; 19,3°/, Al,O,). Analysis of 
the rests also indicate this composition: 4 Na,O. Al,O, .10H,0. 
If to this solid salt we add a very slight quantity of water or 
diluted sodium lye, it must partly be converted into the other alu- 
minate: 4 Na,0.8 Al,O,, 16H,O, while tbe solution gets the com- 
position G (see fig. ID). This conversion could very well be stated 
by microscope. 
