D. Six grams of mineral and 28 of chloride, mixed by thorough grinding, were heated to 350° for fourteen hours; then were reground with 28 grams of fresh NH,Cl and heated for thirty-five hours. Loss of weight, 0.13 per cent; 5.07 per cent of soda was extracted as chloride, plus 0.14 of ammonium chloride unexpelled; 2.03 per cent of silica was rendered soluble in sodium carbonate.

So far, three facts are noticeable. First, the weight of the mineral after treatment is almost exactly the same as before; showing that gains and losses have balanced each other. Second, little silica has been split off. Third, approximately, but not rigorously, one-half of the soda had been converted into NaCl. In A, it was exactly half; in the other experiments, a little less than half. Furthermore, in the sodium chloride dissolved out there is only a very little ammonium chloride, amounting at most to 0. 14 per cent, calculated upon the weight of the original mineral.

In the residue of the analcite after extraction of sodium chloride, abundant ammonia can be detected, with either no chlorine or at most a doubtful trace. If, however, the unleached mineral, still retaining its sodium chloride, be heated strongly, say from 400° up to redness, NHCl is regenerated and given off. Its absence, as such, both from the leach and the residue was repeatedly proved. The ammonia and water retained by the analcite after heating to 350° with ammonium chloride were several times determined; and the following percentages, still reckoned on the original mineral, were found:

Correcting the ammonia for the 0.14 of NH4Cl found in D, the mean value becomes 2.15. This permanent ammonia is not given off upon warming the material with caustic soda solution, and is therefore not present as a salt. The determinations of it were made by three distinct methods, and there is no possible doubt as to its presence and character. The composition of the analcite after the treatment with ammonium chloride may now be considered, with the subjoined combination of the data. The NaCl in A, 11.50 per cent, was in material which had gained 2.18 per cent, and is subject to a correction which reduces the figure to 11.26. In B, C, and D the corresponding correction is so small that it may be neglected. The last column gives the composition of the leached residue, recalculated to 100 per cent, after deduction of NaCl and the soluble silica. The letters refer back to the several experiments, and the little iron is included with the alumina.

The analcite residue, like the original mineral, is completely decomposable by aqueous hydrochloric acid. It may be a mixture, but it seems more probable that it is a definite compound, for it approximates in composition to the formula

H2Na Al SiO24. NH3.

The

This represents a quadrupled analcite formula, in which hal of the sodium is replaced by hydrogen, and with NH3 in place of 4H2O analytical comparison is as follows:

The agreement is not close, but it is close enough to be suggestive and to indicate the character of the reaction which has taken place. It needs, however, verification by additional experiments upon other preparations, and upon analcite from other sources. In this connection it may be well to reiterate that the substance was prepared by very long heating at 350°, and is therefore stable at that temperature.

An interesting feature of these experiments is their harmony with the researches of G. Friedel, who has shown that the water of zeolites may be replaced by ammonia and other substances, without change of the crystalline structure. In the case of analcite, ammonia was taken up to the extent of 2.04 per cent, or almost exactly the amount found

1 Bull. Soc. Min., Vol. XIX, 1896, p. 94.

in our analcite residue. The great difference between Friedel's 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 analogous compounds, the relation between them is expressed by these formulæ :

Analcite....

Analcite residue..

Na AlSiO24. 4H2O.
H2NаAlSigO24. NH3.

That is, the minimum molecular weight assignable to apalcite is represented 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 destruction 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 various 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 Lepierre1 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 representable by fourths, but Friedel's experiments 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 necessary 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 comparison 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 and no presumable errors of manipulation can 'Bull. Soc. chimique, Paris, 3d series, Vol. XV, 1896, p. 561. 2 Bull. Soc. min., Vol. XIX, 1896, p. 363.

account for so great a divergence. If we consult other analyses, as we find them tabulated in manuals like those of Dana and of Hintze, we shall find other cases resembling this, and also examples of variation in the opposite direction, with silica low and an apparent excess of bases. Most analcite gives quite sharply the metasilicate ratios required by the accepted formula; but the variations from it are large enough, common enough, and regular enough to command attention. The analyses are not all covered by the recognized theory, and the apparent irregularities are not fortuitous, but are systematic in character. One explanation of the seeming anomalies is simple and clear. If analcite, instead of being a metasilicate, is really a mixture of orthoand trisilicate, then all of the analyses became intelligible. In most cases the two salts are commingled in the normal ratio of one to one; but in our analcite the trisilicate predominates, while in some other samples the orthosalt is in excess. All reduce alike to the simple expression

NaAIX. H2O,

in which X represents nSiO,+mSiO; a formula which agrees with evidence from various other sources.

For example, analcite may be derived in nature either from albite, AINASi Og, or nephelite, AlNaSiO,, and, on the other hand, alterations of it into feldspars have been observed. Its closest analogue, leucite, has yielded pseudomorphs of orthoclase and elæolite; while leucite and analcite are mutually convertible each into the other. The evidence of this character, the evidence of relationship between analcite and other species, is varied and abundant, and the simplest conclusion to be drawn from it is that which has been given. Every alteration, every derivation, every variation in the composition of analcite points to the same belief. The consistency of the data can not well be denied. In the case of a normal analcite-that is, one which conforms to the usual empirical formula-the expression which best represents these relations is

Al,Na(SiO4)2 (SiO2)2. 4H2O;

and this accords with the minimum molecular weight as determined by the study of our ammoniated residue. Structurally, this is comparable with the formule of garnet, zunyite, sodalite, nosite and leucite; all of which are also isometric in crystallization. The more important of the symbols are as follows:

STEIGER.

That is, analcite and leucite become members of the garnet-sodalite group of minerals, and their relations to nephelite, albite, prehnite, natrolite, etc., natural and artificial, are perfectly clear. In analcite there may be admixtures of strictly analogous ortho- or trisilicate molecules; but these remain to be separately discovered.

Now, these formulæ are not ultimate verities to be blindly accepted. They are simply expressions which represent composition and a wide range of established relationships, and which serve a distinct purpose in the correlation of our knowledge. Properly used, with due recognition of their limitations, they are helpful, and suggest possibilities of research; misused, they may become mischievous. They now satisfy all known conditions, and that is a sufficient warrant for their existence.