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PREFATORY NOTE.

In the following pages there have been brought together a variety of chemical and mineralogical researches, which were carried out in the laboratory of the United States Geological Survey between July 1, 1893, and July 1, 1899. In one sense the bulletin is a continuation of the series represented by Bulletins Nos. 9, 42, 55, 60, 64, 78, 90, and 113; only, unlike them, it reports no miscellaneous analyses. The latter represent by far the larger part of the work done in the laboratory; but most of them are published in other form, in connection with the geological investigations to which they relate. Their repetition here is unnecessary.

F. W.0.

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EXPERIMENTS RELATIVE TO THE CONSTITUTION OF PECTOLITE, PYROPHYLLITE,

CALAMINE, AND ANALCITE.

By F. W. CLARKE and GEORGE STEIGER.

In a series of investigations by Clarke and Schneider, which were carried out in the laboratory of the United States Geological Survey between 1889 and 1892, a number of reactions were examined which shed some light upon the constitution of several natural silicates. The work then begun was unfortunately interrupted for several years; but it is now resumed, with the hope that it may be pushed considerably further.

Two of the reactions studied by Clarke and Schneider were of peculiar interest. First, in the case of talc, it was found that one-fourth of the silica could be liberated by ignition; and that the fraction thus set free was measurable by solution in aqueous sodium carbonate. This reaction suggests that other acid metasilicates may behave in a similar way, and that we perbaps have a means of discriinination between such salts and other compounds which simulate them. In other words, an acid metasilicate may be experimentally distinguished from a pseudometasilicate by the way in which it splits up when ignited. Evidence bearing upon this supposition will be found in the present paper.

The second of the reactions just referred to is that between dry ammonium chloride, at its temperature of dissociation, and various silicates. This involves, in part at least, the action of dry gaseous hydrochloric acid upon the compounds which are studied; and different minerals are very differently attacked. Some are almost completely decomposed, others are affected but slightly; and here again there seems to be a method of diagnosis which deserves further attention. Both reactions suggest the main purpose of the investigation; which is, the fractional analysis of silicates by means of various reagents, in

Bull. U.S. Geol. Survey No. 78, p. 11; Bull. No. 90, p. 11; Bull. No. 113, p. 27.
2 Bull, U.S. Geol. Survey No. 113, p. 34.

order to gain evidence bearing uport their chemical structure. The evidence, at least, is of value, whether the interpretation of it be right or wrong. Each fact helps to the ultimate solution of the central problem, the problem of cokštitution.

PECTOLITE.

The poetolite which was chosen for examination was the well-known radiated variety from Bergen Hill, New Jersey. The mineral was in long, white needles, and apparently quite pure; but the analysis shows that it contained some carbonate as an impurity. Enough of the material was ground up to furnish a uniform sample for the entire series of experiments, and the work properly began with a complete analysis. The results obtained are as follows:

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All of the water was given off at a barely visible red heat; and the figures show that practically all of it is constitutional, a fact which perhaps hardly needed reverification. The analysis gives the accepted formula for pectolite,

HNaCa SizOg.

Does this represent, as is commonly assumed, a true metasilicate! If it does, we should expect that ignition would split off silica proportional to the acid hydrogen, or one-sixth of the total amount. To answer this question several portions of the pectolite were sharply ignited, to complete dehydration, and then boiled each for fifteen min.

utes with a solution of sodium carbonate containing 250 grams to the liter. In the extract so obtained the silica was determined; and three experiments gave the following percentages:

8.96 8. 67 8.42

Mean, 8.68

One-sixth of the total silica is 8.89 per cent; and the experiments, therefore, justify the original expectation. The belief that pectolite is a metasilicate is effectively confirmed.

Upon the unignited pectolite the sodium carbonate solution has a slow decomposing action, both silica and bases being withdrawn. In two experiments fifteen minutes of boiling extracted 2.07 and 2.55 per cent of silica, and by a treatment lasting four days 4.80 per cent was taken out. With water alone similar results were obtained; the action being so rapid, although relatively slight, that pectolite, moistened, gives an immediate and deep coloration with phenol phthalein. By boiling the powdered pectolite with distilled water alone 1.65 per cent of silica was brought into solution, and the ignited mineral, similarly treated for fifteen ininutes, gave 1.78 per cent. The extraction in these cases is really an extraction of alkaline silicate, as the two following experiments prove. In A the unignited pectolite was boiled for fourteen hours with distilled water; and in B the mineral after ignition was subjected to like treatment for four hours. The dissolved matter in each case was determined, with the subjoined results:

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In A, no simple ratio appears; but in B the extracted silicate approximates very nearly to the salt Na Si,03. In each instance the ratios vary widely from those of the original mineral, showing that actual decomposition and not a solution of the pectolite as such has occurred.

In the experiments upon pectolite the heating with dry ammonium chloride was omitted, for the data are already given in the original paper by Schneider and Clarke. In their experiments the mineral was thrice heated with ten times its weight of the reagent to above 3500, and then leached out with water. In the solution 20.50 per cent of lime and 6.95 of soda were found, with part of the manganese; showing that a very considerable decomposition had taken place. Possibly, by

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