the crystalline state and their molecular weights are unknown.

Molybdenum carbonyl, Mo(CO), is a very easily volatile crystalline compound. It is interesting to note that the negative valence of molybdenum (s—e=18—6) is twelve, so that with a covalence of 12 for the molybdenum atom in this compound we again obtain a structure consistent with the valence theory discussed above.

2. INCOMPLETE COMPOUNDS.-These are compounds in which some of the electrons are not arranged in complete layers or sheaths, so that the tendency of Postulate 1 is not completely satisfied. This can only occur as a result of a conflict between Postulate 1 and Coulomb's law or Postulate 3. We have seen that the tendency of Postulate 3 causes the residual charge (v) on each atom to be a minimum. The tendency of Postulate 1, however, is sufficiently strong to force the atoms to take up charges of 3, 4, or even under some conditions, 5 or 6 units, if this should be necessary in order to bring all the electrons into complete layers. Since there must be a limit to the strength of the tendency of Postulate 1 it is not surprising that residual atomic charges greater than 4 or 6 are very rare. Now the atoms of the elements near the middles of the long periods (of 18 and 32 elements), do not become complete even if they do acquire residual charges as great as 5 or 6 units, and it is therefore natural that the tendency of Postulate 3, which must become stronger as the charge increases, should prevent the formation of complete compounds of these elements. There are two types of incomplete compounds to consider.

a. Metallic Substances. Electronegative Atoms Absent.-By Coulomb's law, atoms having only small charges on their kernels, should not be able to take up enough electrons to complete sheaths of 8 or more electrons. Thus if we bring together a number of electropositive atoms there is no way in which the electrons in the incomplete sheaths can rearrange themselves to form complete sheaths. The

5 Mond, Hirtz, Cowap, J. Chem. Soc., 97, 798 (1910).

free" electrons which are thus compelled to remain in incomplete sheaths are responsible for the metallic properties shown by all electropositive elements in the solid or liquid state. It is clear, however, notwithstanding the fact that hydrogen may sometimes function as an electropositive element, that liquid or solid hydrogen should have none of these metallic properties according to this theory, for the sheath to be formed in this case contains only two electrons. The forces acting between the free electrons and the kernels of the atoms in metallic substances, are of the same order of magnitude as in salts, so that metals have about the same range of vapor pressures, hardness, compressibilities, etc., that are shown by salts.

In general, all atoms must be electropositive unless they can take up enough electrons to complete their sheaths and thus act as electronegative atoms. The tendency of Postulate 3 ordinarily prevents the occurrence of negative valences greater than about 4. In the two short periods eight electrons are needed to form a complete sheath so that the elements with kernel charges greater than about 3 can act as electronegative atoms and therefore do not normally show metallic properties. In the 2 long periods 18 electrons form the complete sheath so that about the first 14 of the elements in each of these periods can usually act only as electropositive elements and they thus have metallic properties, when in the elementary form. For similar reasons all the known elements of the rare earth period (the last two being unknown) have metallic properties.

b. Compounds Containing Electropositive and Electronegative Atoms.-As a result of Coulomb's law or Postulate 3, the positive valence of an element is usually limited to a value of 2 or 3 unless particularly strong forces are exerted to draw away electrons, and thus raise the positive valence a few units higher. Thus in the middle of the long periods the charges of the kernels are so great that all the electrons in the sheaths of the electropositive atoms can not be given up even when other atoms are present that can take up electrons. It thus happens that the long pe

riods contain series of elements which all have 3 or 2 and 3 as their principal valences. The atoms of these elements are therefore incomplete. The electronegative atoms in such compounds, however, are always complete.

It is of interest to note that as long as atoms are incomplete there seems to be no tendency for them to have an even rather than an odd number of electrons. For example, the following ions all have odd numbers of electrons: Cr***, Mn++, Fe+++, Co**, and Cu**. This seems to indicate that the remarkable tendency, pointed out by Lewis, for most compounds to contain even numbers of electrons is due merely to the relative abundance of complete compounds as compared to incomplete ones. In other words, the even number of electrons in most compounds results from the tendency of Postulate 1 rather than from any more general tendency for electrons to form pairs.

Many of the compounds of this class, such as ZnO (zincite), Fe,O,, PbS, CuO, etc., show electric conductivity even as solids. This is undoubtedly caused by the relatively large number of electrons in incomplete sheaths. Of course we should not expect all compounds which contain such electrons to show conductivity, for the presence of the electronegative atoms might easily prevent the mobility of these electrons. We need to know much more than we now do about the arrangement of the atoms and their electrons in space before we can predict conductivity in particular cases of this kind.

3. EXCEPTIONAL CASES.-There are some substances or compounds whose structure is not adequately accounted for by the foregoing analysis. A few examples are: N2, CO, CN-, NO. The writer believes these have the single octet structure which he described in his earlier publications. It is probable that acetylene, C2H2, and the carbide ion C2- (in CaC2, etc.) have the same kind of structure. Pease has suggested that they may all have a triple bond structure. This question merits careful study.

Another set of compounds that must have 6 Jour. Amer. Chem. Soc., 43, 991 (1921).

a special structure are various compounds of boron such as B2H ̧.

Most compounds containing molecules of H2O, NH,, etc., are readily accounted for by Postulate 3 but many of these should be considered by methods somewhat different from those developed here.

2

In double molecules such as H ̧O, (in ice), H2F2, and in compounds such as KHF, etc., it seems that the hydrogen nuclei instead of forming duplets with electrons in the same atom, form duplets in which the two electrons are in different atoms. The hydrogen nucleus itself thus acts as a bond in such a case. Latimer and Rodebush' have made a somewhat similar suggestion in regard to hydrogen nuclei acting as bonds. They consider, how. ever, that the hydrogen nucleus acts on two pairs of electrons: one pair in each of the two atoms. It seems to the writer much more probable that the hydrogen nucleus is no more able to attract four electrons than is the nucleus of other atoms. Since the first layer of electrons in all atoms contains only 2 electrons it seems probable that the hydrogen in this case also holds only two electrons and that these form the definite stable group which we have termed the duplet.

The writer plans to consider the quantitative aspects of these valence theories in subsequent papers. It is aimed to put Postulates 1 and 3 into a form that will permit at least rough calculations of the relative stabilities of various substances as measured, for example, by their heats of formation.

IRVING LANGMUIR

RESEARCH LABORATORY, GENERAL ELECTRIC COMPANY, SCHENECTADY, N. Y.,

June 29, 1921

PROFESSOR H. BRUCHMANN

THE men who gave such distinction to botany in Germany during the latter half of the nineteenth century, have mostly gone, the years since 1914 taking heavy toll of those who were left when war broke out. Among the last of the veterans was Professor Bruchmann 7 Jour. Amer. Chem. Soc., 42, 1431 (1920).

whose death occurred on Christmas day, 1920.

A copy of the Gothaisches Tageblatt recently received by the writer contains an interesting sketch of his life, and shows the high esteem in which he was held by his fellow-townsmen in Gotha, where the greater part of his life was spent.

While Bruchmann is, perhaps, not so well known in America as some of his contemporaries, his work was of a very high order, and eminently worthy of recognition, and is quite indispensable to students of the Pteridophytes, which were his chosen field of study.

Helmut Bruchmann was born in Pollow, a small town of Pomerania, November 13, 1847. After his preliminary schooling he studied at Jena, where he became associated with Strasburger, who quickly recognized his abilities, and would gladly have kept him, as assistant in Jena, but financial reasons made it necessary to seek more remunerative employment.

In 1877 he accepted a position as teacher in the high school of Gotha, where he spent the remainder of his life. Later he received the title of professor.

Bruchmann's name will always be associated with his truly remarkable studies on the life history of the European species of Lycopodium. These familiar plants had hitherto baffled all efforts to trace their life history, and Bruchmann spent nearly twenty years at work before he published his monograph in 1898. This is a masterpiece of careful work, and its great value was quickly recognized. The patience required to complete this work will be appreciated when it is realized that in some species six to seven years elapsed before the first germination stages were evident and twelve to fifteen years before the prothallia

SCIENTIFIC EVENTS

FIELD WORK OF THE SMITHSONIAN INSTITUTION

THE Smithsonian Institution has issued its annual exploration report describing its scientific field work throughout the world in 1920. Twenty-three separate expeditions were in the field carrying on researches in geology, paleontology, zoology, botany, astro-physics, anthropology, archeology, and ethnology, and the regions visited included the Canadian Rockies, fourteen states of the United States, Haiti, Jamaica, four countries of South America, Africa from the Cape to Cairo, China, Japan, Korea, Manchuria, Mongolia, Australia, and the Hawaiian Islands.

In an outline of the year's work, the Institution says that

Secretary Walcott continued his geological work in the Cambrian rocks of the Canadian Rockies in the region northeast of Banff, Alberta. The work was hindered considerably in July and August by forest fires, and by continuous stormy weather in September, but the particular questions involved in the season's research were settled satisfactorily and some beautiful photographs of this wild and rugged region obtained. Other geological field work was successfully carried on in various states of the United States by members of the staff.

In astrophysical research the institution was unusually active. Through the generosity of Mr. John A. Roebling of New Jersey, the Smithsonian solar observing station located on the plain near Calama, Chile, was moved to a nearby mountain peak, where the observations will be unaffected by the dust and smoke, and a new station was established on the Harqua Hala Mountain, Arizona, probably the most cloudless region in the United States. From daily observations of the radiation of the sun at these two widely separated stations, it is hoped to establish definitely the value of the "solar constant" observations in forecasting weather. Dr. C. G. Abbot, director of the work, also describes the successful operation on Mt. Wilson, California, of a solar cooker devised by him. With this apparatus it was possible, using only the sun's heat, to cook bread, meat, vegetables, and preserves.

Mr. H. C. Raven represented the Smithsonian on an extensive collecting expedition through Africa from south to north. Although many difficulties were encountered, among others a railway wreck in which two members of the expedition

were killed, Mr. Raven shipped to the Institution much interesting zoological material, which was greatly needed for purposes of comparison in working up the famous Roosevelt and Rainey collections already in the National Museum. Many interesting photographs of the animals, the natives, and the country itself are shown in this account and in that of Dr. Shantz, who accompanied the expedition as a botanical collector. In Australia, a Smithsonian naturalist collected, through the generosity of Dr. W. L. Abbott, specimens of the fast disappearing remarkable fauna of the continent, while Dr. Abbott himself secured a great number of plants, birds, and other natural history material for the National Museum, in various regions of Haiti. A number of other zoological and botanical expeditions are briefly described and illustrated.

THE MEDICAL SCHOOL OF THE UNIVERSITY OF VIRGINIA

AT a session held in Cabell Hall on June 3, the General Alumni Association of the university unanimously adopted resolutions opposing the removal of the medical school to Richmond. An address was made by Dr. Alderman appealing for the preservation of the integrity of the university.

The resolutions as adopted are as follows: WHEREAS, the commission on medical education in Virginia has, by a vote of 5 to 4, recommended the consolidation of the Medical College of Virginia with the medical department of the University of Virginia, and that the consolidated institution be operated as the medical department of the University of Virginia, and located in Richmond; and,

WHEREAS, the overwhelming weight of the testimony of disinterested experts of national reputation opposes, as utterly contrary to the best scientific thought of the day, the separation of the medical department of the University of Virginia from the other departments of the university and favors, with singular unanimity, its retention at Charlottesville; .

...

Resolved, That the General Alumni Association of the University of Virginia hereby expresses its unqualified opposition to the proposed removal to Richmond of the medical department of the university as a step opposed to the interests of the state of Virginia, as injurious to the cause of medical education, as destructive of the integrity of the University of Virginia, and as violative of

those principles of higher education which, established by Thomas Jefferson, have received the sanction of time and of experience.

Resolved, further, The president of this association be and he is hereby instructed and empowered to appoint such committee, make such expenditures and do such other acts and things as in his judgment will best effectuate the purpose of these resolutions and preserve and protect the educational fabric of the state of Virginia.

THE SCIENCE CLUB OF THE UNIVERSITY OF TEXAS

During the academic year 1920-21, the Science Club of the University of Texas, composed of members of the university science faculties, held eight meetings. The following papers were presented :

Oct. 11, 1920. "Some modern conceptions of the atom," by W. T. Mather, Professor of Physics. Nov. 1, 1920. "Habits and instincts of spiders,''

by T. S. Painter, Adjunct Professor of Zoology. Dec. 6, 1920. "Relative birth-rates of white and colored races," by J. E. Pearce, Associate Professor of Anthropology.

Jan. 3, 1921. "The occurrence of latex (milk) in plants," by F. McAllister, Associate Professor of Botany.

Feb. 7, 1921. "Luminescence," by H. B. Weiser, of Rice Institute, Exchange Lecturer from the Houston Philosophical Society.

March 7, 1921. "Species of the genus Schwazerina and their stratigraphic significance," by J. W. Beede, Geologist in the Economic Geology Division of the Bureau of Economic Geology and Technology.

are

The officers elected for the year 1921-22

Dr. H. J. Ettlinger-president.

Dr. T. S. Painter-secretary-treasurer.

H. J. ETTLINGER,

Secretary

THE ROCHESTER MEETING OF THE OPTICAL SOCIETY OF AMERICA

THE Optical Society of America will meet in Rochester, N. Y., on Monday, Tuesday and Wednesday, October 24, 25, and 26, at the Hotel Rochester. In order to provide the maximum opportunity for social meetings of members and guests, arrangements will be made for society lunches and dinners.

The regular sessions for the reading of papers will be open to all interested persons. Members and others desiring to communicate results in optical research are invited to submit titles of papers for the program to the secretary any time before September 25. No arbitrary time limit is set for the presentation of a paper, but each author is requested to estimate carefully the time which will be sufficient to present his paper briefly and intelligibly, and to submit this estimate with the title.

Each title must be accompanied by an abstract (100 to 200 words). Authors are urged to make every effort to present the essence of their papers as cogently as possible in these abstracts. It is expected that they will be printed in the program and in the minutes of the meeting. No titles will be printed to be presented "by title."

Persons having papers ready for publication which can not be presented at the meeting are invited to submit them to Paul D. Foote, editor, Journal Optical Society of America, Bureau of Standards, Washington, D. C.

Because of the optical industries in Rochester it is expected that this will be a particularly interesting meeting. The local committee is arranging for a visit to the Bausch and Lomb Optical Company and the Eastman Kodak Company.

The National Research Council Committee on Physiological Optics has asked the society to form a section on vision. It is hoped to do

this at the coming meeting; and, if a sufficient number of papers on this subject are submitted, one whole session will be devoted to vision and physiological optics.

For further information in regard to the society consult SCIENCE for April 1, 1921. IRWIN G. PRIEST,

Secretary

AMERICAN ENGINEERS IN EUROPE

WITH the presentation of the John Fritz Medal to Eugene Schneider, head of the famous Creusot Works, in Paris on July 8, by a mission of American engineers, came cable advices from London to the national headquarters of the American Society of Mechanical Engineers announcing that more foreign honors had been conferred upon Americans distinguished in the engineering profession.

Ambrose Swasey, of Cleveland, sponsor of the Engineering Foundation and past president of the American Society of Mechanical Engineers, has been elected to honorary membership in the British Institution of Mechanical Engineers, in the British Institution of Mining and Metallurgy and in the British Institution of Mining Engineers. Charles F. Rand, of New York, has been elected an honorary member of the Institution of Mining and Metallurgy, and of the Institution of Mining Engineers. Mr. Rand, who is chairman of the executive board of the Engineering Foundation, has also been made an honorary member of the British Iron and Steel Institute. Other elections announced by cable were those of Colonel Arthur S. Dwight, of New York, and William Kelly, of Vulcan, Mich., to honorary membership in the Institution of Mining Engineers.

The ceremonies in Paris, participated in by a special deputation of thirteen American engineers under the general chairmanship of Mr. Swasey, followed similar ceremonies in London on June 29, when the John Fritz Medal for distinction in applied science was presented to Sir Robert Hadfield, known for his work in the development of manganese steel. The Hadfield award was for 1921 and