<a jj£5 B £ n> ] CONSTITUTION OF ANALCITE. 23 
in otir analcite residue. The great difference between FriedePs method 
of experimentation and ours renders the agreement all the more striking 
and sustains our belief that the mineral and the residue are compounds 
of the same general order. We hope to continue our experiments and 
to extend our investigations to other zeolites. 
If, now, analcite and its derivative, our analcite residue, are analo- 
gous compounds, the relation between them is expressed by these 
formula?: 
Analcite Na 4 Al.,Si 8 0.:.i . 4H 2 0. 
Analcite residue H 2 Na,>Al 4 Si 8 ,., . NH 3 . 
That is, the minimum molecular weight assignable to analcite is repre- 
sented by four times its empirical formula. Other interpretations of 
the evidence are possible, but this appears to be the simplest. The 
water of analcite, as Friedel has shown, must be regarded as water 
only, not as hydroxyl, for it can be expelled by heat without destruc- 
tion of the crystalline nucleus, the anhydrous salt, and is taken up 
again from moist air. But whatever its mode of union may be, the 
amount of water corresponds to the simple molecular ratio which is 
indicated in the formula of the species. One molecule of analcite 
holds a certain definite number of water molecules, and Friedel's 
observations are not incompatible with the idea that these are retained 
with varying degrees of tenacity. This idea is suggested by the vari- 
ous series of fractionation experiments which have been made from 
time to time by independent workers, even though the data are not by 
any means concordant. Thus Lepierre 1 found that half the water of 
analcite was driven off at or below 300°, the other half above 440°. 
In our own experiments three-fourths were expelled at 300°, the 
remaining fourth being held up to a much higher but undetermined 
temperature. In. both series the water fractions are represen table by 
fourths, but Friedel's experiments 2 indicate a continuity of loss in 
weight of quite a dissimilar order. Friedel holds that all of the water 
fractionations heretofore made upon analcite are fallacious, and that 
no definite fractions can be identified, a conclusion strongly supported 
by his own data, even though the proof is not absolutely positive. 
The most that can be said is that the weight of evidence so far is in 
favor of Friedel's contention, but that additional investigation is nec- 
essary in order to reconcile all discrepancies. The full significance of 
the water in analcite remains unknown. 
In order to discuss the constitution of analcite, let us recur to the 
analysis of the mineral itself. It is at once evident from the compari- 
son made on a preceding page that our sample of the mineral varies 
notably in composition from the requirements of theory. The silica is 
2.5 per cent too high, while alumina and soda are correspondingly low. 
No probable impurity a ,i d no presumable errors of manipulation can 
'Bull. Soc. chimique, Paris, 3d seri. a, Vol. XV, 1896, p. 501. 2 JButt. Soc. min., Vol. XIX, 1896, p. 363. 
