million pounds of oil are being hydrogenated annually by catalytic processes in the United States of America, producing fat equal to that obtained from 7,000,000 hogs. Hydrogenation adds over £4,000,000 annually to the value of American cotton-seed oil. Germany, in 1925, exported Haber products valued at more than £4,000,000. Millions of tons of contact sulphuric acid are produced every year. Comparatively little is known about the real nature of contact catalysis and the mechanism of chemical reactions. Various hypotheses have been advanced, but most of these have not been satisfactory.

Professor Hugh Stott Taylor and his co-workers of Princeton have carried out a great deal of experimental work, and a most interesting theory of the catalytic surface has been developed. It has been discovered that a catalyst surface, such as that of nickel, shows a varying capacity to adsorb gas and to promote catalytic change. While the body of a granule of the catalyst is crystalline, i.e., has an ordered arrangement of atoms, it appears that here and there, on the surface of a mainly crystalline granule, there are groups of atoms in which the process of crystallization is not yet complete. According to Professor Taylor, the following representation of a cross-section of a minute portion of such a granule of nickel may serve as an illustration of such an incomplete stage in the crystalline process:

The atoms in the second layer (II) of the granule proper will be surrounded on six sides by other nickel atoms. The atoms in the surface layer will be surrounded by neighbouring metal atoms in all directions except that towards the gas phase. The degree of constraint or saturation imposed by this orderly arrangement of atoms becomes progressively less and less as we proceed outward from the granule proper (I and II) towards the most exposed metal Thus, the uppermost nickel atoms in the above representation suffer only one constraint by reason of their single attachment to the nickel atom

atoms.

immediately below. Further, we may note that the atoms in the edge of a granule have one less degree of saturation than those in the surface proper; atoms at a corner have two less than those in the surface and one less than those at an edge. A surface of a granule may thus be regarded as composed of atoms in varied degrees of saturation by neighbouring metal atoms, varying from those one degree less saturated than interior atoms to those which are only held to the solid surface by a single constraint. It is by this constraint alone that these outermost atoms differ from gaseous metal atoms.

Exposed Metal Atoms.

"A gaseous atom of nickel can combine with four molecules of carbon monoxide to form nickel carbonyl. It is not therefore improbable that exposed nickel atoms, held by only a single valence to the solid surface, shall have a capacity to attach to themselves or adsorb three molecules of carbon monoxide or, alternatively, three molecules, the bonding between. which and the nickel atom is identical with that

obtaining in nickel carbonyl. With the metal attached to the granules by two constraints, two such molecules might be adsorbed. This concept introduces a mechanism whereby both the constituents of a hydrogenation process may be attached to one and the same nickel atom."*

Likewise, the activation of platinum and silver gauzes in catalytic oxidation is believed to be due to a production, by disintegration of the plane-surfaced wire, of metal atoms to a large degree unsaturated and detached from the normal crystal lattice of the metal, and capable of adsorbing several molecular

reactants.

The notion that certain metal atoms are more or less detached from the normal crystal lattice accords with the observations. These outer atoms should have a greater freedom of motion, and should be relatively sensitive to the influence of thermal change. In the case of nickel, for example, the metal is very sensitive to the influence of heat, whereby marked sintering occurs, indicating that the process of crystallization is incomplete.

It is well known that certain metal catalysts, e.g., platinum in the contact process for sulphuric acid, are easily "poisoned" by foreign matter, and their action thereby inhibited. According to the Princeton view, "it is the less saturated catalyst

* [That is to say, the loose atoms at the surface of the catalyst serve as links in effecting a union between atoms or molecules of substances which do not readily react or unite in the absence of the catalyst.]

atoms in the surface which will be the preferred positions of attachment of adsorbed catalyst poisons. As the quantity of poison increases, more and more of the surface atoms will be covered with poison. In the final issue the whole surface will be covered."

Reactions Involving Gases.

As to the mechanism of certain reactions involving gases made up of diatomic molecules, there is evidence that in the presence of catalytic metals some of the gas is present in the atomic condition on the surfaces of the catalysts. To illustrate, there is proof that atomic hydrogen is present on nickel and on copper, and that both diatomic hydrogen and nitrogen molecules yield the corresponding element in the atomic state in the presence of iron. The abnormal activity of monatomic hydrogen is of importance in the problem of hydrogenation catalysis.

Taylor and Marshall have employed, in their work on hydrogenation, hydrogen atoms formed by collision of excited mercury atoms and hydrogen molecules, the hydrogen atoms being produced by allowing hydrogen molecules (H2) to collide with mercury atoms excited by resonance radiation emitted by a cooled mercury arc. It has been demonstrated that hydrogen and oxygen, in the presence of excited mercury vapour, interact to form both hydrogen

A hydrogen atom is regenerated in the second reaction of the sequence, and we have, therefore, a" chain mechanism."

In order to obtain an optimum yield of hydrogen peroxide, the concentration of hydrogen must be as high as possible. Thirty to forty molecules of peroxide are formed for every quantum of light absorbed by the mercury vapour.

Taylor and Marshall have also succeeded in producing formaldehyde (HCHO) by the interaction of carbon monoxide and hydrogen in the presence of excited mercury atoms. The mechanism of the reaction is perhaps as follows:

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our whole system of pre-Christian chronology is based; and among the men of whose office it brings us the official record, there are two or three who figured in some of the most characteristic stories of Roman history.

The Date of the Stone.

The block of marble just found-of which Figures. I and 2 show the two halves*-comes straight down to us from 36 B.C., when the great historical monument of which it forms a part was set up in the course of

*The numeral signs EXL which appear in the margin of each of these photographs occur only once on the stone, in the blank space in the middle. They refer, las we shall see, to the second half. The bar across the first sign was a convenient mark used by Roman stone-cutters to show that the sign in question was to be read as a numeral, not a letter. From this has come the line which we (and the Italians) draw through our L (for libra pound") to show that it denotes pound" has come to be a different

a particular coin, though our thing from the Italian " lira."

In our school-days we mostly regarded dates as afflictions rather than blessings; but in any case we looked on them as having come straight into our school books from heaven (or elsewhere); things that were settled past all dispute and that needed only to be mercifully administered in sufficiently moderate doses by our seniors. If we had guessed that practically every one of the figures which were given us to learn in Ancient History was the result of a complex constructive process carried out by different scholars often involving prolonged discussion-we might have regarded them with less respect but more interest.

The fragment of what are called the Fasti Consulares which has just been identified at Rome, is a new part of the best basis we have for dating events of the history of the Roman Republic; and it shows very

well what that basis really is. The block of marble (Figs. 1 and 2) lay embedded in the ground for many centuries with other ruins of the Roman Forum; but it must have been turned out of its resting-place some two hundred years ago or earlier, and then built into the porch of a nobleman's palace at Rome (21 Via Torre Argentina). Here it was noticed a few months ago by an Italian scholar-Professor P. Mingazzini, who has just published an account of it.* As we shall see, it is a welcome addition to other remains of the same monument which were discovered in the year 1546 and arranged by Michael Angelo

also of the triumphs celebrated by Roman Generals over the enemies of Rome. These lists were continually made up to date and preserved in the Regia. We know, however, that they were recopied (not to say reconstructed) on more than one occasion, for instance, after the burning of Rome by the Gauls in 390 B.C.; and in the course of the general restoration of ruinous or dilapidated temples in Rome which Octavian undertook, the whole Regia was rebuilt, and its records set up in a more splendid form than ever before, deeply cut in letters three-fifths of an inch high on blocks of fine marble twenty inches

The Regia and its Fasti.

Figure 3 is taken from a sketch by Detlessen, made to show the general character of the building on which this block originally stood. It was called the Regia or King's Palace, a name which descends from the earliest period when Rome was ruled by kings. But under the Republic the building was the official residence of the Pontifex Maximus, or High Priest, the head of the State religion. Among the duties discharged by him and his colleagues was the regulation of everything that concerned the calendar, including the official record of the names of the chief officers of State, of the Census held at regular intervals, and

*Notizie degli Scavi, 1925, p. 376; but this part of that journal has only just appeared. A preliminary account of it, however, was given in the Morning Post of March 16th, and the photograph I owe to the kindness of Prof. Paribeni, the Director of the Museo delle Terme at Rome.

and four feet four inches long. The great thickness of the stone, of course, contributed to the solidity of the building of which it formed a part. The Regia stood in the Forum, close to the south-east end, near to the Temple of Vesta; and the list of consuls was contained in the four tables or panels shown in the sketch. The list of Triumphs was cut on the face of four columns on one side. Of the four panels, the two which are on the side of the building took the form of what we should call blind windows; the best preserved of all is the third, i.e., the first of those on the side-wall, which Figure 4 represents in the shape to which it had been restored by the labours of many scholars before the present discovery. (The figures in the margin, of course, are not part of the monument; but they have been added to show the reader the dates of the years covered by the record.)

Now observe the gap between Fragment XVI a

and b, and Fragment XVII a and b. As the monument stood till the new discovery, we had no record of the Consuls in two periods of time: those from 278 to 266 B.C. were on the slab missing from the first column; those from 214 to 208 B.C. were on that missing from the second column. The block newly found supplies this gap almost completely and will shortly be put into its place with the rest; and then visitors to Rome will be able to see the whole panel in just the shape (save for some slight breaks) which was seen every day by Vergil and Horace and Livy and all the other citizens of Rome, to whom the beauty and stateliness of the new building betokened the restoration of

order and peace,

after a century

of civil wars.

'But how do

we know," the reader will ask, "that the dates you have put in the margin are the dates in which these different people respectively held office?" The answer is contained in 340 folio pages of the second edition of Vol. I of the Corpus Inscriptionum Latinarin which

ит,

two or three

pupils of Momm

sen, of whom Wilhelm

collected and arranged

Henzen

other sources; the chief of these is Livy's great History, with late writers like Cassiodorus, who drew from Livy and whose summaries are especially valuable for the long periods covered by the parts of Livy's History which have disappeared.

On so huge and thorny a subject I hardly dare to enter here. But a single example, taken from the newly-discovered fragment, will show the enormous help which these official Fasti have given us in the task of determining the actual dates. The second line of the right hand column of Figure I gives us as the name of one of the Consuls in a particular year (277 B.C.): C. IVNIVS. C. F. C. N. BVBVLCVS. BRVTVS. II that is to say,

was

the chief, in a splendid series of Tables, based on Mommsen's own work in the first edition of the same Corpus, all the evidence from different sources bearing on each one of the dates, carefully discussing doubtful points. The list of Consuls in its briefest form occupies sixty-nine folio pages. Side by side with the record in this inscription or batch of inscriptions, which, as we shall see, represents the official tradition of 36 B.C., Mommsen and his pupils have set the accounts preserved in six or seven

One line is lost on the left and two on the right at the top; at the bottom two lines are lost on the left and one and a half on the right.

†That is to say, all the evidence available before 1893 when this edition was published.

CONSVLVM TRIVMPH. TAB, IV PAR. IV

have found and to be copying out! According to Cassiodorus the Consul's name was Gaius Junius; two other summaries give his name merely as Bubulcus; a third summarizer gives it as Brutus. This official record for the first time shows us what the man's full name really was, and shows also that the other records were perfectly correct-so far as they go-though each of them was incomplete. It would take long to explain fully the apparent discrepancy; here it will be enough to say that one of the commonest methods of forming a list was to mention only the cognomen, i.e., the third name, of each person. This was no doubt the form in which schoolboys had to learn them by heart; and phrases like Horace's Consule Planco (his full name was Lucius