On the basis of efficiencies shown in published reports, an enterprise contemplating the manufacture of chlorine would select the Finlay cell. The selection of the type of cell, however, and the installation of a plant happen to require many other considerations such as initial cost, attendance charges, upkeep, floor space, overload capacity, cost of energy, continuous or off-peak operation, market for products, etc. While it is not to be expected that complete and reliable data on these various features can be available in so new an industry, there are a number of outstanding characteristics of processes and of individual cells that bear on the above named factors.

While diaphram renewal is necessary in cells of the diaphragm type, it is looked upon rather as a matter of cell upkeep than as operating trouble. Where the brine is properly pretreated the cells are operated from. six to twelve weeks or even longer without serious falling off in efficiency or output. The mechanical cleaning of diaphragms in operation has been suggested, but the nature of the stoppage would seem to make this impracticable, if not impossible. Chemical cleansing of the cell pores is also unpromising on account of the activity of the chlorine on one side and of the caustic on the other. The diaphragm type cells are the most satisfactory on the market at present.

Offsetting the many advantages of the mercury cell are the comparatively large investment and large floor space required and the difficulty of removing impurities from the mercury. The high fixed charges can be compensated only by low energy costs, mercury cells being thus limited to regions of abundant water power.

The bell type require comparatively large floor space. Their low energy efficiency is offset by low investment, upkeep, and attendance charges. The possibilities of increasing the energy efficiency by decreasing the operating voltage offers a promising field for experimenters. The voltage above the brine decomposition voltage (2.3) is used entirely in overcoming the internal resistance of the cell. Since the resistivity of the electrolyte is about 400,000 times that of hard cast iron and 5600 times that of carbon, it is evident that, as pointed out above, by far the greater part of the voltage drop in a bell cell is due to electrolyte resistance and a very small part to electrode resistance. The problem, therefore, is to increase the area and decrease the length of the path of the current in the electrolyte and at the same time provide for the removal of the products of electrolysis without the undesirable secondary reactions. Because the area of the electrodes usually varies with the area of current path through the electrolyte and therefore with the voltage, undue importance seems to have been attached to electrode area and electrode-electrolyte contact resistance. Experience has shown that density of current in the electrolyte is the factor of prime importance. If the electrolyte current density factor is taken care of at all points, there will be no question of electrode-electrolyte contact resistance.

The capacity of rating of a cell should be based on the output of products of standard purity with maximum energy efficiency. The overload capacity would then be defined as the maximum rate of production which gives such standard products regardless of energy efficiency. Capacity stated in pounds or kilos of chlorine per 24 hours is definite; expressions such as "a 2000-ampere cell," sometimes used, are without meaning in stating capacities.

The value of overload capacity in the economics of production depends upon the relation among a number of factors. It is evident that to increase the output increase of the current density is required, and to increase the current density higher voltage, resulting in lower energy efficiency and higher energy cost of production, is required, but the higher rate tends to decrease the cost of production by cutting down the fixed charges. It follows that there is a point of maximum economy readily determinable in any given case. Thus it was found that a certain plant operating with highest ampere-hour efficiency at two tons of chlorine a day could be operated most economically at four tons a day. The character of load afforded the central station by electrolytic chlorine plants is most attractive. The low voltage energy of unvarying amperage may, for many types of cell, be taken directly from a rotary converter at the available pressure, say 110 to 500 volts. For example, a type of cell using 1500 amperes at 3.5 volts could be connected 30 in series on 110 volts, in which case the required converter capacity would be 165 kw. Such a plant would produce, say, 2880 lb. of chlorine per 24 hr. Voltage regulation is unnecessary. In addition to these attractive features, such a plant, if equipped with the proper type of cell, permits of offpeak operation.

The increasing demand for chlorine, its numerous products and its by-products must lead to the development of a recognized standard type of cell comparable in efficiency, durability and ease of operation with other standard electrical apparatus. This ultimate type of cell will doubtless have an energy efficiency above 80 per cent; it will operate with little attention, and its elements will require renewing infrequently as do those of a storage battery. Ordinary impurities in the salt and water will have no effect on its efficiency and will be periodically removed as simply as a boiler is blown off.

Many cells now in use cannot be shut down without taking special precautions to prevent mixture of brine and caustic, destruction of anodes, or other bad effects. The ultimate type will be unaffected by interruption of energy supply.

With the development of the efficient and dependable cell for the production of chlorine will come the development of simpler and safer methods for its utilization. Which of the fields of its present application will come to demand the bulk of the output it is impossible to foresee. Most interesting to the chlorine manufacturer, to the central station power salesman and to the industrial engineer is the fact that wonderful growth in the electrolytic chlorine industry appears to lie immediately ahead.

Civil Service Examinations

Metallurgist (Male).-A vacancy exists in the Navy Yard, Norfolk, Va., at $2800 a year. Bachelor's degree in metallurgy or mining engineering and at least three years' experience in metallurgy, including inspecting and testing of metals, are required. Applications must be filed prior to July 29, 1919.

Metallographist (Male).-A vacancy exists at the Engineering Experiment Station, Naval Academy, Annapolis, Md., at $7.52 per diem. Applicant must have bachelor's degree in chemistry, engineering or metallurgy and must have had not less than one year's experience in the use of the microscope in the examination of metals. Examination closes July 29, 1919.

T

I

HE address of Dr. Irving Langmuir delivered at the Buffalo meeting of the American Chemical Society on "The Arrangement of Electrons in Atoms and Molecules" made such a deep impression upon those who heard it, and the potentialities of the Langmuir postulates loom so large as applied to research, that we resolved to give our readers a report on the subject as soon as this could be made ready. The first original paper appeared in the June number of the Journal of the American Chemical Society. Owing to the intense concentration of the text it is not easy reading, even to the average chemist, and in what follows we shall not attempt to cover the field with thoroughness, or even to touch upon problems that require experience in applying the postulates. Our purpose is to write an introductory chapter, and to begin "further back" for the benefit of those who have not followed diligently the voluminous literature of research on the structure of atoms and molecules. We shall not even attempt to make the line clear between the Langmuir postulates and the work of other men in research whose conclusions are in part accepted. We are dealing with a new philosophy of chemistry which differs from that of the present text-books in various concepts, but which provides a definite means of determining upon the arrangement of atoms in combination, as well as that of electrons in atoms and molecules.

PRACTICAL VALUE OF THE THEORY

We shall try to give at least a glimpse of its amazing practicality when applied in the laboratory. It is, in effect, a new angle of attack which calls for new mental processes; and, as with any new tool, these seem difficult at first. When we state, however, that with adequate understanding and experience, it becomes possible to predicate the physical and chemical qualities of a substance, even to its crystalline structure, before it is synthetized; that it opens up a new and workable theory of valence; that it explains the curious manifestations of the elements of the rare earths and other elements in the periodic table, the irregularities of nitrogen, and the magnetic properties of the iron and platinum groups of metals, as but a part of its contributions, we need give no further emphasis to its value as an aid to technology as well as to research. We shall not undertake to make all these facts clear. Our purpose is to lure the reader into a consideration of the subject, so that he may approach Dr. Langmuir's present and future papers with that quality of interest which is warranted by their importance.

For lack of space and with a view to confining ourselves to the simplest features in this article we shall omit discussion of the principle involved in the secon

dary planes (Postulate I) in connection with the position of electrons in atoms of greater complexity, also the magnetic forces as indicated in Postulate V, and the illumination shed upon the great work of Werner, and refer the reader to the first paper in the June number of the Journal of the American Chemical Society for the explanations and a much more comprehensive discussion of the entire subject in a very condensed form.

We are indebted to Dr. Langmuir for a number of extended interviews, and we express our sincere obligations to him for his patience in exposition.

STRUCTURAL RESEMBLANCE OF NO AND CO2

By way of indicating the workings of the theory let us take as an example two gases that we have not heretofore regarded as having any qualities in common: N,O, or laughing gas, and CO,. According to the Langmuir postulates, as we shall try to develop them in part, these gases display a remarkable resemblance in the structure of their molecules, containing each the same balanced number of positive and negative charges, and the same exterior arrangement of electrons, so that, were they magnified to visibility, and the kernels of the atoms hidden from view, we should be unable to tell them apart by looking at them. At least it is a fair guess that by looking at them, under these conditions, we should be unable to distinguish them, one from the other. Then we conclude that they must have certain physical properties in common. The figures which follow have not been published elsewhere at the present writing; we are indebted for them to Dr. Langmuir, who will present them later on with detailed explanation in the Journal of the American Chemical Society, but they will serve to indicate the points of remarkable similarity in the physical properties of two gases which Dr. Langmuir concludes to be similar in structure. The records are taken from unrelated pages of published works:

Both gases form hydrates, N,O.6H,O and CO,.6H,O. The vapor pressure of the hydrate of N,O is 5 atmospheres at 6 deg. C., while the hydrate of CO, has this vapor pressure at 9 deg. C. The heats of formation. of the two hydrates are given respectively as 14,900, and 15,000 calories per gram-molecule.

The surface tension of liquid N,O is 2.9 dynes per sq.cm. at 12.2 deg., while CO, has this same surface tension at 9.0 deg. C.

Thus NO at any given temperature has properties practically identical with those of CO, at a temperature of 3 deg. lower.

These results indicaate the similarity of the outside structure of the molecules.

DISAGREEMENT IN FREEZING POINT

There is one property, however, that is in marked contrast to those given above: the freezing point of N,O is -102 deg. C. while that of CO, is -56 deg. This may be taken as an indication that the freezing point is a property which is abnormally sensitive to even slight differences in structure. The evidence seems to indicate that CO, is slightly more symmetrical and has a slightly weaker external field of force than that of N2O.

It would be hard to find such an array of coincidences unless there were reasons for them, and it is one of the purposes of this paper to show reasons for them, as we proceed.

All of these figures have been gathered by painstaking research in the past. They were uncorrelated and uninteresting. But in the light of this theory we find them ranging themselves into such subtle correlation as to cause them to function as parts of that greater whole which men of research are ever trying to discover. For decades these figures have been available. But in this case, as in that of other bodies which we shall consider later, the identical physical characteristics of those of like structure have remained unobserved.

II

At the end of the paper we present the postulates upon which the work is based, and we shall refer to them from time to time as we proceed. But, going "further back," as we promised to do, let us consider every atom as made up of two component parts: the electro-positive charges concentrated in the nucleus of each atom, which is individual and peculiar to each element, and the electrons which are electro-negatively charged, and which, from their positions about the nucleus, neutralize the positive charges on it. The electrons are arranged in a definite configuration about the nucleus of each atom. They are not of necessity held absolutely still. There is no reason why they may not move about, but the area of activity of each electron that forms a part of an atom is circumscribed within limits of space similar to that of its neighbor. Unlike the nuclei which, as we have just said, are held to be peculiar to each element, we consider the electrons to be all alike.

Now let us bear in mind the atomic numbers of the elements in the order of their atomic weights in the periodic table. They are: H, 1; He, 2; Li, 3; Be, 4; B, 5; C, 6; N, 7; 0, 8; F, 9; Ne, 10; Na, 11; Mg, 12; Al, 13; Si, 14; P, 15; S, 16; Cl, 17; Ar, 18; K, 19; Ca, 20; Sc, 21; Ti, 22; V, 23; Cr, 24; Mn, 25; Fe, 26; Co, 27; Ni, 28; Cu, 29; Zn, 30; through to U, 92.

ATOMIC NUMBER COINCIDES WITH ELECTRO-POSITIVE CHARGES

Thanks to the brilliant Moseley of Manchester, England, killed as a private soldier in the flower of his youth in the Gallipoli fight, we have confirmation of the statement that the atomic number of each element in the periodic table and the number of electro-positive charges on the nucleus of its atom are the same. Thus from the above we read that the number of positive

charges on the nucleus of the hydrogen atom is 1; that of the lithium atom is 3; carbon, 6; nitrogen, 7, and so on, so that the table of atomic numbers is also that of the positive charges on the nucleus of the atom of each element. From this we gather also that the nucleus of the atoms of no two elements can be the same, and we learn, too, that the table of atomic numbers gives, in addition to the foregoing, the number of electrons that are attached to, and form part of, every atom of every element. There must be an electron to neutralize every positive charge, because the difference between an atom and an ion is that in the former every positive charge of the nucleus is satisfied with an electron, and is therefore neutral, while in an ion this is not the case. In an ion there are either more or fewer electrons than will completely balance the positive charge of the nucleus of the atom, or the nuclei of the atoms, which constitute it.

In acknowledging and accepting in part certain theories of W. Kossel and G. N. Lewis, Dr. Langmuir carries them further, with various changes and extensions, but, as already stated, for the sake of brevity we shall not attempt to indicate the specific authorship of each idea.

III

By themselves electrons repel each other, but in the presence of positive charges they show a disposition to arrange themselves into definite groups; they indidate a law, or series of laws, of configuration, and this is the first step in the present work. If, then, these groupings, these configurations, may be found complete in the most stable of the elements, and incomplete in others, we may infer that in the inert gases the electrons are satisfied, that they have fulfilled their tendency to conform to certain arrangements, and that the activity of other elements is due to the drive to conform as nearly as possible to the complete, and therefore inert, elements. The author of these postulates will have nothing to do with metaphysics in the development of his theories of the constitution of atoms and molecules, but we cannot resist the observation that in this pair-forming and octet-forming nature of electrons about positive charges we find suggested the tendency in nature toward a condition of balance and rest which is the basis of the great postulate of Gautama Buddha, and the substance of the ancient philosophy of the East.

HELIUM THE MOST STABLE Element

Different elements do not behave the same; they differ in their nuclei and in their arrangement and number of electrons, but in this striving to become as nearly as possible like the fixed gases we find the key to all chemical phenomena. It behooves us, therefore, first to consider the most stable element, which is helium. The

FIG. I

atomic number of helium being 2, the positive charge of its nucleus is 2, and it has two electrons. How are these arranged? There being but two they cannot follow an isometric system: the simplest would be the tetragonal system, having, like the earth, a polar axis and an equatorial plane (Postulate I). We imagine these two electrons as held by the positive charges of the nucleus very much as though the nucleus were in the center and the electrons each in the half of a complete shell, say, like a walnut-shell, that surrounds it. Neither electron crosses the plane which divides these two hemispherical shells. We might picture, as in

This must be the most permanent arrangement of electrons about a nucleus: one electron in each half of a spherical shell, and neither trespassing upon the territory of the other. And while there is no reason to regard the electrons as stationary, save that each keeps

within what we call its cell, it will be convenient for

us to consider each as occupying its average position, which would be on an axis perpendicular to the plane which divides them. Here we have a complete satisfaction of the positive and negative charges with almost no force extending beyond the atom in any direction. Let us say the electrons have achieved a position of complete balance and contentment, thus making helium the most permanent substance known. Because there is practically no external force about the atoms, and the primary disposition of its electrons to form pairs is satisfied, the atoms do not form molecules; they remain independent and inert. So independent and inert are they that not only is He a gas, owing to the lack of external force about its atoms, but these atoms are readily separated, and its boiling point is therefore only 4 degrees above absolute zero. We have, then, in helium, the achievement of the first electronic ideal: the grouping in pairs about a positive charge. Such a central part we consider to be common to all atoms except that of hydrogen: the nuclei varying from 2 to 92 positive charges, according to the element, and the first pair of electrons invariably next to the nucleus.

neon.

V

FIG. 2

FIG. 3

The next element to helium in point of stability is Its atomic number being 10, we must find an ideal arrangement of its ten electrons. The nucleus has ten positive charges, and the conclusion is that the first pair group themselves about the nucleus, just as in helium, leaving eight positive charges to be satisfied. These eight electrons arrange themselves in a second shell outside that containing the pair, four in either hemisphere of the outer shell, and each in its own cell. A top view would appear as in Fig. 2, with the nucleus and pair hidden under the outer shell. A perspective view would be as in Fig. 3. These eight electrons, four in either hemisphere of the outer shell, we call an octet. This shell is twice the diameter of that including the pair below it, and its surface is four times as great. This is in order to give the same space or room to each cell. There are eight cells, and every cell in the outer shell of neon is occupied. Now since we hold that chemical activity emanates mainly from the outer shell of electrons, there is no occasion for chemical activity in neon. And bearing in mind this greater chemical activity of the outermost shell we shall follow G. N. Lewis in calling all that part of any atom that is within the outer shell, its kernel. The second disposition of electrons is to group themselves into octets, and here they have done it. We have a pair, and an octet, all balanced, all filling every available space, and so there is no chemical activity to neon. It is inert; it is a gas; it has a low boiling-point, and it does not form molecules. It is completely satisfied as

it is, and next to helium it is the most stable element. The next element in order of stability is argon, atomic number 18. This is just like neon, except that, according to Postulate IV, each cell of the second shell contains 2 electrons, making 2 in the first and 16 in the outer shell. This is also a permanent gas. krypton, atomic number 36, we have two in the first shell, 88 in the second, and have 18 still to dispose of. The third shell will contain 18 electrons; 9 in each

In

hemisphere. One of these 9 electrons will go to the pole, and the remaining 8 will be distributed symetrically about it. The same thing happens in the other hemisphere. With xenon we have krypton as the kernal (except that the nucleus has 18 more positive charges) and the 18 more electrons are distributed in the same manner in the third shell, making 2 in each cell, and including one more in a cell at each pole. Niton follows as the last, with 32 electrons in the fourth shell, 16 in each hemisphere.

In other words, we assume these inert and stable elements to be made up of successive and consecutive groups of electrons about the nucleus of each, consisting of first the nucleus, next a pair of electrons, and then consecutive octets and double octets with a pair in the polar position whenever there is an odd number of electrons to be provided for in each hemisphere. According to Postulate IV, all inner shells must have their full quota of electrons before the outer shell can contain any, but we note that in the inert elements the outside shells have their full quotas also. This is the very reason for the stability and inactivity of these elements; the electrons are ideally placed, they are electrically balanced, there is a minimum field of external force about the outer shells, therefore they all are gases, and have low boiling points.

No element other than the inert gases has its outer shell satisfied, i.e., every cell of its outer shell occupied, and therefore the electrons in the outer shell are always striving to make pairs or octets with some other electrons. This is the basis of all chemical combination and reaction. We shall try to make this more evident as we proceed.

VI

When we consider hydrogen, atomic number 1, we have but a single charge and a single electron. We have not even a pair. The lone electron is ever trying to form a pair, and therefore the atoms pair off in molecules. Note, please, in Postulate VI that a stable pair may be held by two hydrogen nuclei. Of course the hydrogen molecule is not as stable as an inert gas, but compared with a single hydrogen atom which has an exceedingly short time factor for its separate existence, the hydrogen molecule is very stable. It has the lowest boiling point of all substances except He, being but 20 deg. absolute. Due to such complete saturation within itself its external force is slight, and it shows slight chemical activity until it is split up into atoms. The old status nascendi theory in regard to hydrogen worked well in that it referred really to unpaired hydrogen atoms. If we take from a hydrogen atom its single electron we have left of course the hydrogen ion.

Lithium with its atomic number of 3 has three electrons, of which two form a pair about its nucleus and which constitute the lithium ion, while the third is easily detached, because it tends to form pairs or octets. We read in Postulate VI that the two atomic ker