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repeated treatments with ammonium chloride a complete decomposition might be effected, but this question is one upon which it seemed unnecessary to spend further time,
The empirical formula for pyrophyllite, AlHS1,08 is apparently that of an acid metasilicate, and the mineral is therefore peculiarly available for fractional analysis. The compact variety from Deep River, North Carolina, was taken for examination, and a uniform sample was prepared. Analysis gave the following results:
.73 29. 16
If, now, pyrophyllite is an acid metasilicate it should break up on ignition in accordance with the equation
2A1HSI:0.= Al Siz0y + Si0, + H2O.
That is, one-fourth of the silica, or 16.18 per cent, should be liberated. The mineral itself is very slightly attacked by boiling with the sodium carbonate solution, and in an experiment of this kind only 0.72 per cent of silica was dissolved. Upon ignition under varying circumstances the following data were obtained:
Ignited ten minutes over a Bunsen burner, and then extracted with sodium carbonate solution, 1.51 per cent of Si0, dissolved.
Ignited fifteen minutes over a Bunsen burner, 1.89 per cent became soluble.
Ignited ten minutes over a Bunsen burner and then fifteen minutes over the blast, 2.84 per cent of silica was liberated.
These results are of a different order from those given by pectolite and talc, and raise the question whether pyrophyllite, despite its ratios, is a metasilicate at all. So far as the evidence goes, it may with propriety be regarded as a basic salt of the acid H.Si,O5, and its formula then becomes
Si205 = Al — OH. This formula is at least as probable as the metasilicate expression, which latter rests upon assumption alone. Still other formule, but of greater complexity, are possible; but until we know more of the genesis and chemical relationships of pyrophyllite, speculation concerning them would be unprotitable.
By heating with dry ammonium chloride, pyrophyllite is very slightly attacked. In two experiments it lost in weight 6.17 and 6.30 per cent, respectively. The excess of loss over water is due, as we have proved, to the volatilization of a little ferric and aluminic chloride. The residue of the mineral after this treatment contained no chlorine, so that no chlorhydrin-like body had been formed. The formation of such a compound, the replacement of hydroxyl by chlorine, would, if it could be effected, be a valuable datum toward determining the actual constitution of the species.
The simplest constitutional formula for calamine, the one which is generally accepted, represents it as a basic metasilicate, Si0=(ZnOH)2. In this the bydrogen is all combined in one way, and so, too, is the zinc. In all other possible formulee, simple or complex, the hydrogen as well as the zinc inust be represented as present in at least two modes of combination; a condition of which, if it exists, some evidence should be attainable. Our experiments upon calamine have had this point in view; and we have sought to ascertain whether water or zinc could be split off in separately recognizable fractions. Our results, in the main, bave been negative, and tend toward the support of the Iisual formula; but the data are not conclusive, although they seem to be worthy of record.
The beautiful wbite calamine from Franklin Furnace, New Jersey, was selected for study, and gave the subjoined composition:
Incipient red heat.
Here no clear and definite fractionation of the water is recognizable, at least of such a character as to suggest any other than the ordinary formula for calamine.
Upon boiling powdered calamine with water practically nothing went into solution, but by boiling with the solution of sodium carbonate 0.25 per cent of silica was dissolved. After ignition at a red heat, only 0.14 per cent of silica became soluble in sodium carbonate, and after blasting, only 0.24. In these experiments a very little zinc was dissolved also; but there was no evidence that any breaking up of the mineral into distinguishable fractions had occurred. In a hot 10 per cent solution of caustic soda both the fresh and the ignited calamine dissolve alınost completely; but boiling with aqueous ammonia seems to leave the mineral practically unattacked. All experiments aiming to extract a definite fraction of zinc while leaving a similar fraction behind resulted negatively.
By heating with dry ammonium chloride, calamine is vigorously attacked, and gains in weight by absorption of chlorine. In two experiments the mineral was intimately mixed with three times its weight of powdered salaminoniac and heated in an air bath for several bours to a temperature somewhat over 4000. A large part of tbe residue was soluble in water, and the percentage of this portion, together with the percentage increase in weight, is given below.
Gain in weight...
A conversion of calamine into the chlorhydrin, SiO3 (ZnCl), would involve a gain in weight of 15.34 per cent. Complete conversion into 2ZnCl2 + SiO2 implies an increase of :38.14 per cent. The figures giveu lie between these two; and are indefinite also for the reason that there was volatilization of zinc chloride.
In two more experiments the calamine, mingled with three times and four times its weight of ammonium chloride, respectively, was heated for an hour and a half to bright redness in a combustion tube. The zinc chloride which was formed, volatilized, and was collected by suit. able means for determination. It corresponded to 59.6 and 59.0 per cent of the original mineral, calculated as zinc oxide; which indicates a nearly complete decomposition of the calamine into 2ZnCl, + Si0,. The residue was mainly silica, with a small part of the zinc, about half of the silica being soluble in sodium carbonate solution. Here again no definite fractionation of the mineral could be observed.
Finally the action of dry hydrogen sulphide upon calainine was investigated. The mineral was heated to redness in a current of the gas, and gained perceptibly in weight. The percentage data, reckoned on the original calamine, were as follows, in two experiments:
Gain in weight...
6.00 16. 45
6.43 20.95 24.12
Complete conversion of calamine into 2ZnS + Sio, implies a gain in weight of 5.80 per cent; and it is therefore evident from the figures of the second experiment that the limit of change was approached very nearly. The 24.12 of sulphur taken up is quite close to the 26,53 per cent which is required by theory. About eight-ninths of the calamine had undergone complete transformation. Again, no definite fractionation was detected.
The hydrogen sulphide reaction was examined still further with reference to the temperature at which it becomes effective. Even in the cold calamine is slightly attacked by the gas, but its action is unimportant until the temperature of 400° is approximated. Then it becomes vigorous and the reaction goes on rapidly. A few experiments with willemite showed that it also was attacked by hydrogen sulphide, but less vigorously than calamine.
ANALCITE. Analcite, from many points of view, is a species of peculiar interest, and of late years it has received a great deal of attention. Its formula may be written in various ways, especially as regards the interpretation of its one molecule of water; but evidence too often has yielded before preconceived opinion. Additional evidence is now available, partly from the experiments of Friedel and partly from the data obtained during the present investigation.
The analcite examined by us was in well developed crystals from Wassons Bluff in Nova Scotia. A uniform sample was prepared as usual, and the analysis given below is contrasted with the theoretical composition required by the accepted empirical formula NaAlSi,06 H,0.
The fractional water determinations were made by heating in an air bath to constant weight at each temperature up to 300° and finally over the direct flame. The first fraction, at 1000, is evidently hygroscopic or extraneous water, which can be disregarded. The remainder of the water, 8.38 per cent, belongs to the species. The significance of the analytical figures will be considered later.
Upon boiling the powdered analcite with sodium carbonate solution, 250 grams to the liter as in all the preceding experiments, 0.73 per cent of silica was extracted. After ignition the mineral in two determinations yielded 1.46 and 1.38 per cent respectively. The splitting off of silica is therefore very slight; and one of the formulæ proposed by Doelter,' Na, Al,Si,08 +2H,Si03, may be set aside as improbable. Metasilicic acid or an acid metasilicate can hardly be present in analcite, although the possibility of a neutral metasilicate, as indicated by the empirical formula, is not excluded. By Doelter's formula one-half of the silica ought to be removable.
Upon heating analcite with dry ammonium chloride results of a remarkable character were obtained. Sodium chloride was formed which could be leached out by water and measured, while ammonia free from chlorine was retained by the residue to a notable and surprisingly stable degree. The experiments in detail were as follows:
A. Analcite, mixed with four times its weight of ammonium chlorido was heated. for four hours to 350-. There was a gain in weight of 2.18 per cent, and 6.10 per cent of soda, or one-half of the total amount, was converted into NaCl, which was leached out by water, examined as to its purity, and weighed. In the residue 1.20 per cent of silica was extractable by sodium carbonate, showing that no more splitting off had occurred than was previonsly observed. The gain in weight, as will be seen from subsequent experiments, is due to the fact that all of the NH CI had not been driven off; or else that more water was retained.
B. Analcite was ground up with four times its weight of NH,CI, heated for several hours, reground with another fourfold portion of chloride, and heated to 350° for twenty-one hours. Gain in weight, 0.08 per cent; 5.57 per cent of soda was extracted as chloride.
C. Analcite heated to 3500 for eight hours, with four times its weight of NH,CI. Loss of weight, 0. 10 per cent.
Neues Jahrb. für Min., 1890, Vol. I, p. 133.