compounds of this class. The value of the stere in a number of unsaturated compounds is found to be Hydrocarbons, 6·87; 7·09; 6·93; 6·99. Esters and ethers, 7·14; 7·13. The values vary, practically, within the same limits as in the aliphatic compounds. As regards aromatic compounds, it would seem to follow, from the identity in the volumes of benzoyl and amyl compounds, as indicated by Kopp, as well as from the corresponding relation between the isobutyl and phenyl compounds, that CH comprises the same number of steres as CH—that is, 13. Of these, 5 are occupied by hydrogen; so that the carbon group C occupies 8 steres. 6 5 6 4 9 The values of the stere in a number of aromatic compounds are as follows :— Hydrocarbons, 6·85; 6·94; 6·98; 7·00; 6·95; 7·04; 7·04; 7.04; 706; 6·84. Other compounds, 6·91; 6·87; 7·05; 6·97; 7·16; 7·26; 7.50; 7.28; 7·14; 6·96; 7·07. The value of the stere here also varies within the usual limits; it is comparatively small for the hydrocarbons (6.870), larger in the case of the alcohols, and still larger in that of the esters (7·2-7.5). These relations, if substantiated, would seem to indicate that the law of volumetric combination among the masses of liquid molecules is essentially not more complex than the law of combination between those of gaseous molecules. There is one consideration which is vital to the whole question, and to which, therefore, a brief reference must be made. It relates to the choice of conditions under which the values we term molecular or specific volumes are really comparable. Although Horstmann and Lossen have advanced reasons against the practice, contending that at any other temperature, say 0°, relations similar to those now established are made manifest, it has been the custom, in accordance with Kopp's direction, to compare the specific volumes of liquids at the temperatures of their respective boiling points under a standard atmosphere. Whether, however, the temperature of the boiling point, under these circumstances, is a truly comparable condition is open to question. It has been urged by 10 18 38 Horstmann that, since what we call atomic volume is the space not merely filled by an atom, but also that in which "it moves, and lives, and has its being," it is not a priori probable that a temperature which differs, say, by 300°, as, for example in the case of CH (boiling point 1°) and CH (boiling point 317°), these volumes will be the same. Moreover, as pointed out by Bartoli, the boiling point cannot, in the nature of things, be a strictly comparable condition, since it is affected by pressure to a different extent in the case of different liquids. Objections of even greater weight may be urged against the suggestions of Tschermak and Krafft, to take the melting point as a comparable state. No doubt, theoretically speaking, a valid condition should be when pressure, volume, and temperature are expressed in terms of their critical values. But that certain regularities in the molecular volumes at the boiling points have, in spite of this, been discovered, may be explained, as Guldberg has shown, when we compare the values of T,, the absolute boiling point, with those of T, the absolute critical temperature; in those cases in which these two constants are known, the ratio T/T, approximates to . Hence it follows that qualities like molecular volumes, which alter only slowly with temperature, are comparable at the ordinary boiling points (Zeits. für. Physikal Chem., 5, 374). It ought, perhaps, to be stated that subsequent observations show that the so-called "corresponding temperatures" deduced from Van der Waal's generalisations have not that degree of validity as temperatures of comparison which they were originally assumed to possess. Indeed, the present condition of knowledge warrants the statement that Kopp's original method of comparison is as valuable as any yet indicated. Kopp continued to the last to interest himself in the problem which had been the mainspring of his scientific activity. Shortly before his death he gave to the world, through the Annalen (250, 1889, 1), a critical account, written with the dignity and calm that befits the well-earned leisure of a veteran controversialist, of the many strivings which had been made to solve it since the tentative efforts he put forth in his thesis of 1838. We rise from the perusal of this memoir with the conviction that, after all, the work thus summarised takes us but little beyond the threshold of the fundamental truth of which its author was the first to perceive the indication. As yet we see through a glass darkly, and know only in part; but with the fuller light of a rapidly advancing knowledge, we shall most certainly get an insight into the causes which affect the universality of Kopp's conclusions. The discrepancies, if we could only read them aright, contain within them the clues to a broader generalisation which will more clearly connect the chemical nature of molecules with their physical attributes. Our experimental material will soon be sufficient for the basis of this generalisation, even if it is not so already. What is wanted is another Kopp to interpret it correctly. XII DMITRI IVANOWITSH MENDELEEFF "SCIENTIFIC WORTHIES," No. XXVI.-NATURE, 27TH JUNE 1889. DMITRI IVANOWITSH MENDELEEFF was born on 7th February (N.S.), 1834, at Tobolsk, in Siberia. He was the seventeenth and youngest child of Ivan Paolowitsh Mendeleeff, Director of the Gymnasium at that place. Soon after the birth of Dmitri his father became blind, and was obliged to resign his position, and the family became practically dependent upon the mother, Maria Dmitrievna Mendeleeva-a woman of great energy and remarkable force of character. She established a glass-works at Tobolsk, the management of which for many years devolved entirely upon her, and on the profits of which she brought up and educated her large family. The story of Mendeleeff's youth is given in the preface to his great work On Solutions, which he dedicated to the memory of his mother in a passage of singular beauty and power. Having passed through the Gymnasium at Tobolsk, Mendeleeff, at the age of sixteen, was sent to St. Petersburg, with the intention that he should study chemistry at the University, under Zinin. He was, however, transferred to the Pedagogical Institute, the aim of which was to train teachers for the District or Governmental Gymnasiums throughout the Empire. The Institute (which was abolished in 1858) was established in the same building as the University, and was divided into two Faculties -Historico - philological and Physico- mathematical. Men deleeff attached himself to the natural sciences, and thus came under the influence of Woskresenky in chemistry, of Emil Lenz in physics, of Ostrogradsky in mathematics, of Ruprecht in botany, of F. Brandt in zoology, of Kutorga in mineralogy, and of Sawitsh in astronomy, most of whom were professors of the same sciences in the University. Whilst at the Institute he wrote his first paper on "Isomorphism," and on the termination of his course of instruction he was appointed to the Gymnasium at Simferopol, in the Crimea. During the Crimean war he was transferred to one of the Gymnasiums at Odessa, and in 1856 he was admitted to the degree of Magister Chemia of the Physico-mathematical Faculty of the University of St. Petersburg, and was made Privat-Docent in the University. Even at this early period of his career we find Mendeleeff speculating on the great problems with which his name is inseparably connected. The relations between the specific gravities of substances and their molecular weights had begun to attract increased attention. Kopp had just published the first instalment of that long and laborious series of experimental observations which constitutes the real foundation of all our knowledge concerning the specific volumes of liquids, when the young Siberian philosopher laid a number of theses on problems relating to specific volumes before the Physicomathematical Faculty of the University. He pointed out that magnetic elements have smaller specific volumes than diamagnetic elements. He also showed that Avogadro's supposition, that electro-positive elements have larger specific volumes than electro-negative elements, was in accordance with the greater number of well-established facts. When we remember how slowly, in spite of the powerful advocacy of Williamson, the ideas of Laurent and Gerhardt, and what came to be known as the modern French school, found favour in this country, it is remarkable, as indicating the radical and progressive character of his mind, and the keenness of his |