Изображения страниц
PDF
EPUB

Further instances of "small series," each consisting of seven members, known or unknown, are the following:

[merged small][merged small][merged small][ocr errors][ocr errors][ocr errors][ocr errors][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small]

Thus M. Mendeleeff considers that all the functions by which the dependencies of the properties of the elements on the atomic weights are expressed appear as periodic. The properties change in accordance with the increasing atomic weights, and are then repeated in a new period with the same regularity as in the former. If we examine his scheme we must admit that it brings admitted relations into a very prominent light. Such groups as fluorine, chlorine, bromine, and iodine; as sulphur, selenium, and tellurium; as nitrogen, phosphorus, arsenic, and antimony; as calcium, strontium, and barium; or as potassium, rubidium, and cæsium, though their respective members are placed in different series,-fall into positions which well agree with their respective analogies. Even the trinity of the commercial world-gold, silver, and copper-fall in the same horizontal line across the series; gold being a representative of its companion metals in a higher series. A further study of Table II. will bring to light many more curious instances of such representation, which we submit lend a powerful support to M. Mendeleeff's arrangement.

As a matter of course the mere arranging the elements in one arithmetical series would thrust these analogies totally out of sight. As completely would they be hidden if the series were made to consist of any other number of elements. M. Mendeleeff's classification is shown in two tables taken from the translation of his memoir in Liebig's "Annalen." He admits that not all the known elements can be introduced into the small series. Thus in Table I. we see iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum forming an appended eighth group, concerning which the author remarks that they are all grey, all very sparingly fusible, their fusibility increasing in each line from iron to nickel, from ruthenium to palladium, and again from osmium to palladium. Between the corresponding members of the even and the odd small series (except the two first) there is a distinct difference, whilst the corresponding members of the even and again of the odd, series show a close analogy.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

Thus if we recur to the four series above mentioned :—

[merged small][merged small][merged small][merged small][ocr errors][ocr errors][ocr errors][ocr errors][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][ocr errors][ocr errors][merged small][merged small][merged small]

Here it is at once evident that there a decided analogy prevails between the corresponding members of Nos. 4 and 6, and again of Nos. 5 and 7. But between Nos. 4 and 5, 5 and 6, or 6 and 7, there is no such analogy.

Table II. shows the elements as arranged in " great series." In Series I. stands hydrogen alone. This reminds us of a remark made lately by Prof. F. Guthrie, that very generally the commonest bodies are the most anomalous. Series II. contains the seven elements from lithium to fluorine inclusive, these two first groups being designated typical." Series III. contains also seven elements. Series IV. contains fourteen bodies, which, when the three blanks indicated by M. Mendeleeff have been filled up, as one of them already is by the discovery of gallium (ekaaluminium), will be raised to seventeen.

This "great series" consists of the two "small series," No. 4 and No. 5, with three of the non-serial elementsiron, cobalt, and nickel-interposed between them. The great series No. 5 is composed of sixteen known elements, and a blank space is left for a body not yet discovered. The small series here embraced are Nos. 6 and 7, and again three of the non-serial elements-ruthenium, rhodium, and palladium-are interpolated. The great series VI. is very imperfect, comprehending only four elements, which are placed parallel with the first four bodies in Nos. IV. and V. Great series VII. is more perfect; it contains parts of two small series, and again three non-serial elements-osmium, indium, and platinum. Here, however, we are struck with a difficulty: between the atomic weights of tungsten (W=184) and osmium (Os=195) there is the gap of II. Now if M. Mendeleeff concluded that two undiscovered elements, eka-aluminium and eka-silicium, must exist to fill up the interval of 10 between Zn=65 and As=75, in great series IV., why may we not with equal right calculate on the discovery here also of two unknown bodies? But should this be hereafter found to be the fact, the correspondence between the members of Series V. and VII. will be deranged. Gold will occupy the position corresponding not with silver, but with cadmium; mercury VOL. VII. (N.S.)

Y

will figure as the representative of indium; thallium, of tin; lead, of antimony; and bismuth, of tellurium; changes which will not commend themselves to the approval of chemists. Altogether we find that the difference between the successive atomic weights, in parts of the series where M. Mendeleeff does not suspect-or at least does not indicate an absent element, ranges from 1 to 5. What will then become of the interesting harmonies which the scheme exhibits if some undiscovered element should crop up to fill some of the larger of these intervals? We certainly do not find that the author shows any reason why such an event should be improbable. M. Mendeleeff himself declares that the Periodic Law cannot be harmonised with the Atomic theory without inverting known facts.

It will, we think, be evident to the reader that-splendidly as the discovery of gallium has fulfilled the deductions drawn from the law under consideration-the subject is still in its infancy, and that future research is abundantly needed to confirm, to modify, or to extend. We should suggest to chemists and physicists a course parallel to what we have recommended to biologists in the case of the Darwinian hypothesis. We would say-Take up the law provisionally, and work with it. One of the most essential steps is the search for "eka-silicium," conducted, as the author proposes, by the spectroscopic examination of titaniferous minerals and residues. The contents of certain sealed papers which M. Lecoq de Boisbaudran has deposited with the Institute, and in which he has explained his special ideas on the classification of the elementary bodies, must be awaited with interest. Readers who would wish to pursue this subject further will find detailed information in the "Journal de la Soc. Chimique Russe " (i., p. 60); in Liebig's "Annalen" (Supplement-Band viii., p. 183, 1871); and, if they understand the Russian language, in M. Mendeleeff's work, “Foundations of Chemistry" (vol. ii.). As far as the "periodic law" may be considered established, it seems to us most decidedly to contradict the hypothesis of some sixty primordially distinct bodies, and to exhibit our present elements as products of the evolution of something to us yet unknown. For that something it must be the task of chemists to search.

II. ON THE PROBABLE ORIGIN AND AGE OF THE SUN.

By JAMES CROLL, LL.D., F.R.S.,

Of H.M. Geological Survey of Scotland.

HE total annual amount of radiation from the whole surface of the sun is 8340 x 1030 foot-pounds.

To

maintain the present rate of radiation it would require the combustion of about 1500 lbs. of coal per hour on every square foot of the sun's surface; and were the sun composed of that material it would all be consumed in less than 5000 years. The opinion that the sun's heat is maintained. by combustion cannot be entertained for a single moment. Mr. Lockyer has suggested that the elements of the sun are, owing to its excessive temperature, in a state of dissociation, and some have supposed that this fact might help to explain the duration of the sun's heat. But it must be obvious that, even supposing we were to make the most extravagant estimate of the chemical affinities of these elements, the amount of heat derived from their combination could at most give us only a few thousand years additional heat. Under every conceivable supposition the combustion theory must be abandoned.

It is now generally held by physicists that the enormous store of heat possessed by the sun could only have been derived from gravitation. For example, a pound of coal falling into the sun from an infinite distance would produce by its concussion more than 6000 times the amount of heat that would be generated by its combustion. It would, in fact, amount to upwards of 65,000,000,000 footpounds an amount of energy sufficient to raise 1000 tons to a height of 5 miles.

There are two forms in which the gravitation theory has been presented the first, the meteoric theory, propounded by Dr. Meyer; and the second, the contraction theory, advocated by Helmholtz. The meteoric theory of the sun's heat has now been pretty generally abandoned for the contraction theory advanced by Helmholtz. Suppose, with Helmholtz, that the sun originally existed as a nebulous mass, filling the entire space presently occupied by the solar system, and extending into space indefinitely beyond the

« ПредыдущаяПродолжить »