These two run partly parallel with one another; but a deviation in the parallelism appears, which is full of suggestiveness. The peaks of the curves representing oxides shift distinctly to the right of the curve representing chlorides as the atomic weight increases. Lithium marks a maximum with both curves, but the oxygen curve lags greatly at the succeeding peaks, having its maximum with lanthanum at the atomic weight 139,1 and shifting over as far as lead above 200. This simple fact standing alone would perhaps mean but little, but other similar facts seem to point in the same direction. For example, the property of electro-positiveness, exhibited by the alkali metals, instead of reappearing in copper, has been carried over with diminished intensity to zinc; and finally, among the higher atomic weights the cusp has deserted mercury (the analogue of zinc) and gone as far afield as thallium. Clearly the rate of progression which determines electro-positiveness has a longer "wave-length" than that which determines valence, if we may describe the periodicity of these zigzag curves as waves. Again, the tendency toward low melting point unquestionably likewise progresses with a longer "wave length" than most of the other properties. In the first complete period, nitrogen, oxygen, fluorine, and neon all have very low melting points. At each recurrence of these groups with higher atomic weights the melting point rises, whereas with each recurrence of the immediately following alkali metals the melting point falls. By the time antimony is reached, this analogue of nitrogen has a melting point as high as 900° absolute, whereas the next alkali metal has the lowest melting point of all these metals. Clearly the property of melting has shifted toward the right. Other examples of a similar kind have been pointed out by others, for example, the wellknown displacement from strict periodicity of argon, cobalt, and tellurium all point to an unequal rate of progression in isolated cases. Thus, this phenomenon seems to be a general one; the various properties of material seem to oscillate with varying rhythms as the atomic weights increase. The variation is so great that one may almost suspect not only varying rhythms but also rhythms represented by different types of mathematical functions.

These facts suggest a possible reason for the great irregularity of the last part of the periodic table. May it not be that the nature

1 The essential data for discovering this generalization, namely, the heats of oxidation of the metals having great affinity for oxygen, are as follows: Lithium, 72; sodium, 50; magnesium, 72; potassium, 43; calcium 76; rubidium, 42; strontium, 71; cæsium, 41; barium, 67, and lanthanum, 74. These values correspond with gram-equivalents, that is, combination with 8 grams of oxygen, and are expressed in kilogramcalories. The typical oxide is always meant. The figures rest chiefly upon the recent work of Rengade, de Forcrand and Guntz. References to most of the papers are to be found in Abegg's "Handbuch der anorganischen Chemie." The work of Guntz is published in Compt. rend., 1903, vol. 136, p. 1071; 1905, vol. 140, p.863; Bull. Soc. chim., 1906 (iii), vol. 35, p. 503. The work on lanthanum was done by Matignon, Ann. Chim. Phys., 1906 (viii), vol. 8, p. 426. The heat of oxidation of beryllium is not accurately known, but since the oxide may be decomposed by magnesium at high temperatures, the value is very probably less than 70 calories per gram-equivalent.

of the elements is determined by several fundamental tendencies which may be compared to the Mendelian characters of the modern theory of heredity? If these characters recur at different intervals as the atomic weight increases, a given rhythm occurring at first would necessarily be obliterated toward the end of the system. To change the analogy and borrow a term from the nomenclature of light, we may say that the tendencies which produce the curves in this diagram, might first reënforce and afterwards interfere with one another, because they possess different wave lengths. At first, overlapping might accentuate one set of properties; later the changing relation might annihilate this set of properties and cause another. Thus, all the varieties of material may be functions of some few fundamental characteristics which progress at different rates as the atomic weights increase.

Any attempt to discover the nature of these fundamental tendencies must be of a highly speculative character. In our ignorance we can not distinguish between cause and effect. The well-known definite relations of the spectrum lines suggest that at least one of the essential requirements for the existence of an atom may be susceptibility to certain definite harmonic vibrations; those compressible atoms capable of vibrating in certain rhythms may be permanent, whilst other aggregations may be unstable. The gap in the periodic system where ekaiodine and ekacæsium should be, and the amazing instability of the elements immediately following, supports the notion.

But here we have a cosmic puzzle for future solution. To-day we lack adequate data; we are blocked at every turn by our ignorance; therefore, the immediate problem is to discover and test each step as carefully as possible. When the facts have been ascertained, man will have a solid basis upon which to build his future superstructure of theoretical interpretation.

The quest is not dictated by mere curiosity alone. All organic life is actuated by chemical energy, and exists in a mechanism and environment composed of chemical substances; and the effort to understand these essential conditions of human existence constitutes one of the most important objects of human endeavor. Superficial observation of the complex phenomena of life can do but little; as Faraday well knew, patient study of the fundamental laws of the physical universe alone can help to unravel the interwoven threads. Health, well-being, and a profound philosophic outlook are alike dependent upon the result. No one can predict how far we shall be enabled by means of our limited intelligence to penetrate into the mysteries of a universe immeasurably vast and wonderful; nevertheless, each step in advance is certain to bring new blessing to humanity and new inspiration to greater endeavor.

THE PRODUCTION AND IDENTIFICATION OF ARTIFICIAL

PRECIOUS STONES.1

[With 3 plates.]

By NOEL HEATON, B. Sc., F. C. S.

During recent years the production of artificial stones on a commercial scale has become an accomplished fact, and a great many misconceptions and misleading statements have been made as to the relation which these productions bear to natural products on the one hand and imitations gems on the other. It may therefore be of some use to make the matter clear by describing as fully as circumstances permit what has been done in this direction and what has not been done; what is practicable and what is impracticable in the present state of our knowledge.

I suppose there are few subjects of interest from so many points of view as that of precious stones. The beauty and rarity of fine specimens has from time immemorial rendered them the most treasured of possessions. With the romance that surrounds this aspect of the question we have nothing whatever to do to-night, except to bear in mind that on account of their great value men have for centuries strained their ingenuity to solve the mystery that surrounds the origin of such stones, and amass wealth by producing them at will instead of by the laborious and highly speculative process of digging for them in the earth.

Until the development of modern science and accurate methods of investigation this problem resisted all attempts at solution, and it is, in fact, only within the last few years that the artificial production of any species of gem on a commercial scale has become practicable.

Of course, one can cut the Gordian knot by preparing a colorable imitation of the real thing, but that is quite another matter, and I want to make it quite clear at this point that I propose to limit the term "artificial" to such productions as possess the same chemical composition and physicial constants as the natural stones, differing from them only in minute details consequent upon their being produced in the labora

1 Read before the Royal Society of Arts, Wednesday, April 26, 1911. Reprinted by permission from Journal of the Royal Society of Arts, London, No. 3049, Vol. 59, Apr. 28, 1911.

tory instead of being dug out of the earth; all other makeshifts being properly described as "imitations." The production of imitation gems is by no means a modern invention, as is doubtless well known to you. To go no further back than the time of the Roman Empire, the master glassmakers of the dawn of our era, whose skill and knowledge of glassmaking one appreciates more highly the more one investigates the industrial life of those times, were able to imitate almost any precious stone exactly, as far as outward appearance went, in colored glass— and not only the transparent gems, but the structure of such semiprecious stones as agate, cornelian, lapis, and porphyry. It would be quite out of place to devote any time to-night to this historical aspect of imitation gems, but I can not refrain from alluding to the remarkable examples of such imitations found by Mr. Woolley at Karanog,1 from which it is difficult to resist the conclusion that in quite early times Nubia was the center of this industry. To judge by the stories one reads about jewels in those times-stories of the Emperor Comnenus, for example-one suspects that the glassmakers turned their skill in this direction to some account and considerable profit on behalf of an ignorant and somewhat credulous aristocracy; for in those days, and, in fact, until quite recently, not only was the nomenclature of gems very vague, but methods of identification were chiefly remarkable for their nonexistence.

The chief criterion of a precious stone was its color, so much so that throughout medieval times blue glass was known as sapphire and green glass as beryl, etc., giving rise to the legend that in the time of Queen Elizabeth windows were glazed with sheets of beryl. As the tendency still lingers to regard all red stones as rubies and green as emeralds, and so on, I would like to make it clear at this point that color is really quite an accidental property of precious stones; the substance of which nearly every species of transparent gem is essentially composed is colorless, and the color is really produced by minute proportions of impurity.

This being the case, we find that on the one hand the same species of gem stone may exist in a large variety of colors, and on the other hand that a color characteristically associated with one gem may often be found in another having essentially different composition and properties. Owing to this confusion it was very difficult to draw the line between a genuine and imitation stone until the various species of gem stone were accurately defined and their names clearly associated with particular composition and properties, the determination of which forms at the present time a means of distinguishing one from another,

1 Karanog, by C. L. Woolley and D. Randall. MacIver: Philadelphia Museum, 1910.

2 This is quoted in Hollingshed. We read in Theophilus (II, cap. xii) of "tabulas saphiri pretiosas ac satis utiles in fenestris." In a previous paper (Journal, Mar. 15, 1907) I have shown how the name jet was variously applied.