as fuel, the advantages of which are the ease with which it can be regulated, the completeness of its combustion, the readiness with which cleanliness can be maintained, the high heating power of such material, etc. The requirements of such a gas are, 1st, it should consist of combustible constituents only; 2d, it should be possessed of high heating power; and, 3d, it should produce on burning compounds of low specific heat. Hitherto coal-gas has been the only gas available for heating, and, notwithstanding the disadvantages attending its use, has proved itself a cheaper, more effective, and more easily managed fuel than coal, wood, or other forms of solid heat-giving material. Latterly, however, the so-called water-gas, produced by passing superheated steam over anthracite coal at full redness, has come forward with much promise, improved machinery of preparation allowing it to be easily and cheaply produced on the large scale. Though the heating power of water-gas is only about one fifth of that of ordinary coal-gas, yet the cost of the gas is so much less that an actual saving of from one third to two thirds is effected by its use. By the use of oxygen in the blast a gas of very high heating power might be produced.

Long has made a series of experiments on the decomposition of steam by ignited charcoal for the production of watergas. In his earlier experiments the results were complicated by the evolution of absorbed gases from the charcoal. When this source of error was allowed for, it was observed that no fixed relation existed between the carbonous oxide and the carbon dioxide present. But the author noticed that the carbonous oxide was directly as the amount of charcoal present in the tube. Hence it is evident that hydrogen and carbon dioxide are at first formed, and then that the latter gas is reduced by the excess of ignited carbon. If, however, there be an excess of steam present, this is reduced, and carbon dioxide again formed.

Professor Church makes the curious observation that the deterioration of the leather binding of library books, which is often rendered quite friable in time, is brought about by the action of the sulphurous gases given off in the burning of common coal-gas. He has noticed that it is the books on the uppermost shelves of the libraries that are the most affected a fact which, as the combustion products in gradu

ally cooling and descending would reach the uppermost ranges of shelves first in their descent, is made quite understandable. He asserts that he has found in the leather bindings of certain old library books that had become quite brittle as much as eight per cent. of sulphuric acid. Late researches on the permeability to gases and vapors of various materials used for building purposes have demonstrated that when not saturated with moisture, bricks, sandstone, tufa, mortar, and cements are permeable; while granite, porphyry, slate, alabaster, and limestone are practically impermeable. The sanitary bearing of these observations is obvious.

Muter has proposed a method of detecting the addition. of glycerin to milk for the purpose of maintaining its normal specific gravity when it is watered. The residue after evaporation is treated with a mixture of alcohol and ether, and the residue of the evaporation of these solvents is examined for glycerin. If found, its amount must be determined by making a complete analysis of the milk.

Peckham has investigated the cause of the explosion of the flour-mills in Minneapolis in May last, and gives it as his opinion that the explosion was due to the ignition of the fine dust of flour, with which the mill was filled, by sparks coming from millstones which had been allowed to run dry. In the dust-house connected with these stones several hundred pounds of dust a day settled under ordinary circumstances.

A correspondent of Nature writes from Burton-on-Trent that explosions during the grinding of malt, due to the ignition of the fine dust in the air, are not uncommon. Any fine impalpable powder, such as flour, sugar, coal- dust, wooddust, may be thus the cause of serious explosions.

Clémandot has patented in England a process for producing the beautiful iridescence on glass which has lately attracted attention. The glass is simply treated, under pressure and at a temperature of 120° to 150°, with a ten to twenty per cent. solution of hydrochloric acid. The colors are produced by interference.

Silliman has invented a process for making Britannia metal articles sonorous by heating them for fifteen or twenty seconds to 5° below the melting-point in a paraffin bath.

MINERALOGY.

By EDWARD S. DANA, Ph.D.,

YALE COLLEGE, NEW HAVEN, CONNECTICUT.

GENERAL MINERALOGICAL PROGRESS.

The past year and those which have immediately preceded it have been years of very important advance in mineralogy, marked by a decided increase in the number of those interested in the science, and a corresponding increase in mineralogical investigations. Until very recently there has been. but one mineralogical journal, and even in this-the longknown Jahrbuch für Mineralogie - the space was shared with geology and palæontology. In consequence of this fact, the memoirs of the few active workers in this branch of science were scattered through a large number of chemical and physical journals and of society transactions.

Now, however, there is the Zeitschrift für Krystallographie und Mineralogie, published by Professor Groth at Strasburg, of which the second volume in nearly seven hundred pages is completed this year. There are also the Mineralogische Mittheilungen, of Professor Tschermak, a journal which, for several years, was published at Vienna in connection with the Yearbook of the Austrian Geological Survey, but which this year has commenced an independent existence in a new form with an increased range of topics. There is also the Mineralogical Magazine of Great Britain and Ireland, of which the second volume is now being published. It is the organ of the British Mineralogical Society. In addition to the above, the Crystallological Society of London, founded in 1877, also publish a series of Proceedings. Finally, there must be mentioned the "Société Minéralogique de France," which was organized in March, 1878, and which, with Professor Des Cloizeaux, of Paris, as the president, is showing a high degree of activity. The meetings of the society are held about once a month, and five of their Bulletins have already been issued.

Each one of the above-mentioned journals gives, in addi

tion to the original articles, a more or less complete summary of mineralogical papers printed elsewhere. In consequence of this almost every paper bearing upon the science, wherever published, sooner or later finds mention in one of these half-dozen periodicals, and hence the range of mineralogical literature is narrowed down and brought within the reach of all those interested in what is being done.

RECENT PUBLICATIONS.

The number of independent works on mineralogy which have appeared within the past year is not large. Prominent among them stands the descriptive "Catalogue of the Mineralogical Collection of the Strasburg University." This is a quarto volume of nearly three hundred pages, prepared by Professor Groth. It is a work of more general importance than its name would indicate; for it contains not only a catalogue of the individual specimens in this exceptionally fine and complete collection, but also full crystallographic descriptions of the different species. In many cases these descriptions are in fact real monographs, and contain a large number of new facts.

The veteran mineralogist and poet of Munich, Von Kobell, has issued a fifth edition of his excellent little "Mineralogy." The great work undertaken by Schrauf of Vienna-the "Atlas of Forms of Crystals"-has been advanced one stage farther towards completion by the publication of the fifth part. This work contains the figures of the various forms of the crystals of the different species. These species are arranged alphabetically; and as the author has not yet completed the third letter of the alphabet, it will be seen that the end is still far in the future. The first part was issued in 1865. A new book on "Mineralogy," of a somewhat practical and elementary character, has been published in England: the author is Mr. J. H. Collins, editor of the Mineralogical Maga zine.

In this country there has recently appeared a new edition of Dana's "Manual of Mineralogy," an elementary work of about four hundred and fifty pages. The previous edition bears the date of 1857. A new edition of Brush's "Determinative Mineralogy" has been published, in which the mineral formulas have been altered so as to correspond to the

modern chemistry. An important addition to the literature of the science is Mr. G. W. Hawes's volume on the "Mineralogy and Lithology of New Hampshire," which forms a part of Professor Hitchcock's "Survey of the State."

RESEARCHES IN PHYSICAL MINERALOGY AND CRYSTAL

LOGRAPHY.

M. Dufet has made a series of experiments in regard to the indices of refraction in mixtures of isomorphous salts, and has arrived at the conclusion that the differences between the indices of a mixture of two isomorphous salts and those of the component salts themselves is in an inverse ratio to the number of equivalents of the two salts which enter into the mixture. Although obtained with artificial compounds, the results have an important bearing on the many series of isomorphous minerals.

The effect of increase of temperature on the indices of refraction of the natural sulphates of barium, strontium, and lead (barite, celestite and anglesite) has been investigated with great accuracy by Arzruni. He concludes that an increase of temperature diminishes the three indices in each of the species named, but to an unlike degree, though in an analogous manner. He finds also that the directions of greatest, mean, and least expansion bear no relation to the three axes of optical elasticity.

Sorby has published additional explanations of the method of determining the indices of refraction in thin sections, mentioned in the last volume of the Annual Record. The principle involved is indeed not original with him, but he has given it a new and more extended application. It promises to be of very considerable practical value. Another method of obtaining the indices of refraction has been redescribed and elaborated by Kohlrausch, which is of easy application and gives quite accurate results. It is based upon the determination of the angle of total reflection of the given substance when observed in a medium-as carbon disulphidewhich has a higher index. Determinations made by him on a variety of substances, both isotrope and optically uniaxial and biaxial, gave most satisfactory results.

The papers of Professor J. P. Cooke upon the haloid salts of antimony contain some facts which have an important