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of the V,O3. In one case, unfortunately, the air could not have been fully expelled, for the solution after decomposition was blue instead of green and much less oxygen was required in titration than when the color was green.
The contents of the tube, still warm, were poured into fairly hot freshly boiled water and titrated rapidly. Iron and vanadium were then reduced by HS gas, the latter boiled out in a current of CO2, and titration repeated on the hot liquid. The solution was then boiled with ammonia, the precipitate fused with Na,003, leached with water, and the residue again fused with Na2CO3 and leached to remove the last of the vanadium. This residue was then fused with KHSO,, dissolved in dilute H2SO4, boiled first with H2S and then in a current of CO2, and the liquid titrated for total iron. The solution held titanium which was then estimated colorimetrically,
The first of the titration results gave the effect of all iron, assuming its existence as Feo, and of all vanadium that might exist in a lower state of oxidation than V205. The second gave all iron as FeO and all vanadium as V204. Deduct from both the figure for FeO and the remainder gives that for vanadium. In this way two very concordant results were obtained for total vanadium as V,0s, which were supplemented by tests on portions used for other constituents, but only one was obtained for the vanadium as it exists in the mineral, a second being vitiated by evident oxidation during decomposition in the tube. As a check, however, a fresh sample of unpurified mineral was similarly treated, and it was found that fully nine-tenths of the vanadium existed as V203, a result confirming the single test on the purified material which showed 93.5 per cent as V,03. It is not impossible that slight oxidation had iaken place even in these cases, and I feel justified in assuming with Genth that the vanadium should be considered wholly as V203.
In the other portions analyzed the vanadium was likewise titrated in V20, condition, but only after separation from iron, titanium, and alumi. num by fusion with Na,003, extraction with water and separation of dissolved alamina by ammonium carbonate. A second fusion of the residue and of the precipitated alumina was necessary in order to extract all the vanadium. These numerous manipulations render the figures for Al,03 perhaps the least trustworthy of all, but the average given is probably not far from correct.
The iron is assumed to be present as FeO; and the titanium to belong to a foreign mineral, since a test on unpurified material gave much more, namely, 1.50 per cent TiO2, without accompanying increase in FeO, which latter observation seems to exclude ilmenite as the source of the titanium.
Both the iron and magnesium are supposed to belong to the roscoelite, since they were found by Genth in nearly the same amounts and no recognizable iron or magnesium minerals were noticed in the purified powder.
'Any sligbt trace of vanadium remaining will impart a bright yellow color to the cold KHSO,, fusion, a test which proved useful more than once during the analysis.
For comparison, the mean of Roscoe's analyses and that one of Genth's considered by himself to be his best are also given in the table below.
Very marked differences are apparent in the three analyses by different chemists. If titanium was present in the material analyzed by Genth and Roscoe, as is very probable, their high results for alumina are in great part at least accounted for. It is inconceivable how Genth obtained his value for water by ignition, since the mineral oxidizes when heated in air. In fact the oxidation in one of my own analyses, after allowing for loss of water as ascertained by direct weight, was almost what theory requires for the oxidation of V,0, to V,0, and of Fell to Fe,03, or 5.14 per cent instead of 5.27 per cent. It may fairly be assumed that his water was weighed directly after expulsion by ignition of the powder. Roscoe's figures for water, if not for moisture, must be affected by error, probably arising from the unsuspected oxidation of vanadium.
Analyses of roscoelite.
Amount used..... 0.3000g. 0.2531g. 0.26359. a0.1560g 0.20389. Mean.
1. 13 1. 15
2. 01 8. 56
H2O below 1039 C.
a 4.94 per cent oxygen used for complete oxidation instead of 5.27 needed for all V as V,0, and Fe as Feo.
o Equivalent to 23.59 per cent V,03.
From the column of means of my own analyses the following ratios are obtainable:
159 . 113 .022 .041 . 110 .229
The entire absence of manganese and of calcium in my own and Genth's samples tends to confirm the suspicion that Roscoe's material was far from pure. It is to be remarked, however, that my figures for vanadium agree quite closely with his and differ widely from Genth's.
Discrepancies of this kind are not necessarily to be ascribed to faulty analyses. It is well enough known that in any one species of mica various molecules must sometimes be assumed to exist in different proportions, and the general formula for such a species can only be arrived at by comparison of a series of analyses of different varieties. Hence, in view of the lack of any simple ratios, the deduction of a definite and final formula from my data is not justifiable. Further analyses are needed of new and very pure material from other locations, even if these be not far removed from the source of the present material. Nevertheless, in the hands of an expert very unpromising data may often be made to afforıl positive indications, and that this is true in the present case the following discussion by Prof. F. W. Clarke clearly shows:
CHEMICAL CONSTITUTION OF ROSCOELITE, BY F. W. CLARKE.
The ratios given in the foregoing new analysis, used directly, lead to the following empirical formula for roscoelite:
Here H to K and Mg to Fe are as 2 to 1. Between 0 and Si, however, the ratio is not simple, and lies below the orthosilicate and above the trisilicate proportion. Since in many micas the groups $io, and Siz0, are replaceable, that suggestion may be followed out here; and then the formula reduces to
From this expression, applying Clarke's mica theory, the mineral may be regarded as a molecular mixture of the three compounds
3. SiOEKH, Al-S103V
in the ratio 21:22:159, or nearly 1:1:8. Upon reducing the analysis to 100 por cent, after throwing out the Ti0, and the water lost below 280° as extraneous, we get the following comparison between the results found and the theoretical composition:
This comparison, based on the ratio 21:22: 159, is as satisfactory as could be expected.
Of these component molecules the first represents the normal phlogopite type, the second is a trisilicate alkaline biotite, and the third, which forms 74.5 per cent of the whole mass, is a muscovite in which two-thirds of the aluminum have been replaced by vanadium-in short, a vanadium muscovite. Ordinary muscovite is Al;(SiO4)3KH., and whether a corresponding V:(SiO4)3KH, exists can be determined only by analyses of roscoelite from other localities, and so learning its range of variation. That vanadium may replace aluminum is shown by the fact that Piccini has prepared true vanadium alums. That roscoelite is essentially a vanadium muscovite seems to be fairly well established. As for the molecule Al2(Si,O3)3K H,, its existence is indicated in some other micas, and in Simmler's “helvetan" it seems to be the dominant molecule.
NOTE.—A full discussion of the mode of occurrence of roscoelite, with historical data relative to the species, is given by Mr. H. W. Turner in the American Journal of Science, 4th series, Vol. VII, June, 1899, p. 455.
Samples of the peculiar micaceous mineral named mariposite by Silliman were collected at the Josephine mine, Bear Valley, Mariposa County, California, by H. W. Turner in 1894. According to Turner it resembles talc optically, but chemically it appears to be one of the illdefined substances known, for want of a more precise name, as pinite. Two varieties were analyzed-one white, the other green, but neither analysis leads to any definite formula. The data are as follows:
10ccurrence described by Turner in Am. Jour. Sci., 3d series, Vol. XLIX, 1895, p. 377.
No water was lost below 3000. The reaction for lithia was very strong. The color of the green mariposite is evidently due to chromium.
11. Two SULPHATES FROM MONTANA.
Mr. W. H. Weed collected in the St. Paul mine, near Whitehall, Montana, a magnificent specimen of a compact soluble fibrous sulphate, supposed to be melanterite. It seemed to be a filling between fragments of broken rock. Outwardly it was white from dehydration, but at some depth the unaltered green mineral was to be found. This had the following composition:
.077 21. 88