When the surface is a cleavage plane from a crystal, so that the surface atoms are arranged in a regular lattice, the amounts of different liquids (or gases) needed to saturate the surface would probably frequently stand in stoichiometric relations with each other.

In fact the experiments with oil or adsorbed films on water have already shown that these stoichiometric relations are very common. Thus it was found that the number ot molecules of different fatty acids adsorbed per unit area was practically the same for all the acids from propionic up to cerotic. Similarly the number of molecules of stearic acid per unit area was three times that found for tristearine, &c.

It is evident that the configurations of the adsorbed molecules in general are of great influence in determining the number of molecules that can be adsorbed per unit area. This phenomena is, however, nothing more than steric hindrance. In adsorption phenomena, particularly on solid bodies, this steric hindrance must be of very farreaching significance, much more so for example than in the fields ordinarily covered by organic chemistry.

alcohol.

absence of chemical combination, but that it is simply a result of steric hindrance.

It remains to explain why Gurvich's experiments showed that the volumes adsorbed were the same for all the liquids. It must be noted that Gurvich allowed the adsorption to occur in saturated vapours, and that equilibrium was not reached for from fifteen to twenty-five days. Under such conditions every small cavity must fill up completely with liquid because of the decrease of vapour pressure caused by the concavity of the surfaces in the pores of the absorbent. This is a purely secondary phenomenon, being dependent only on the surface tension of the adsorbed liquid, and not on the forces acting between the absorbent and the liquid.

We must picture the processes occurring during the adsorption of, for example, ethyl alcohol by charcoal as follows:-The hydroxyl groups of the alcohol are attracted to the carbon atoms, so fhat as many carbon atoms as possible come into contact (or combine) with the hydroxyl groups. The ethyl groups fill up many of the small cavities, and in other ways prevent the hydroxyl sub-groups from coming into contact with the carbon atoms. The larger pores or cavities are, however, covered over saturated it is evident that these cavities must also with a single layer of molecules. When the vapour is gradually become filled with liquid. But this is to be classed as a capillary phenomena and not as adsorption. It bas, for example, nothing to do with the forces acting between the carbon atoms and the hydroxyl groups.

Suppose we consider the adsorption of two such stances as methyl alcohol and phenol. Since the phenyl group will necessarily occupy more space than the methyl group, the number of molecules of phenol per unit area of a saturated surface will be less than that of methyl We might still expect that the number of phenol mole. cules would bear a simple relation (such as or ) to the number of methyl alcohol, but when we take into account the thermal agitation and the kinetic interchange which must occur, it appears more probable that the relative numbers of molecules adsorbed would bear an incommensurate ratio. This would be especially true if instead of a cleavage surface we should give a surface of an amorphous body as absorbent.

Now in the case of porous bodies such as those employed in Gurvich's experiments, there are cavities of nearly all possible sizes and shapes. It is obvious, therefore, that the phenomenon of steric hindrance will become of dominating importance, and that even in the case of a series of homologous acids or alcohols we should no longer expect to find stoichiometric relations. For example, the number of ethyl alcohol molecules which could attach themselves to the walls of a small cavity would be less than the number of methyl alcohol molecules which could be similarly attached. This difference will become more and more marked as the size of the cavities becomes smaller.

This absence of stoichiometric relationship, therefore, is not to be regarded as evidence that the forces involved are not chemical in nature. It is merely the result of purely geometrical factors. In fact, apart from reactions involving primary valence forces, it seems that stoichio metric relations are the exception rather than the rule, and that where these relations do hold it is merely the result of particularly favourable geometric conditions.

The heat of adsorption is determined in general by the interaction of the active groups and the atoms of the solid body. Thus in Table VI. we see that those groups which cause oils, &c., to spread on water surfaces are just those which cause an increase in the heat of adsorption.

the double bond,

Those groups or radicals are –OH, =~0, –COO–, –NHz,-0–.

The parallelism between these heats of adsorption and the phenomena described in the early part of this paper could hardly be more striking. There can be no reasonable doubt but that the causes of the adsorption are in both cases fundamentally similar.

Let us now consider from the viewpoint of our theory the three reasons which led Gurvich to decide that these adsorption phenomena are not due to chemical forces.

1. We have already seen that the absence of stoichiometric relationship cannot be taken as a proof of the

Under these conditions it is only natural that the volume

absorbed should be about the same for different liquids, since it is simply a measure of the total volume of the larger pores. The amount truly adsorbed is much smaller, and in the case of the three alcohols given in Table VI. is probably quite accurately proportional to the observed heat of adsorption. The three values, 218, 172, and 109, for methyl, ethyl, and amyl alcohols, adsorbed by Fuller's earth, indicate how marked is the effect of steric

hindrance.

Gurvich experimented with 4150 sq. cm. of silver foil in a small tube. This was probably crumpled up loosely and squeezed into the tube. In any case it would be practically impossible to get such a large surface into a tube between adjacent pieces of foil. These capillary spaces in without having an enormous number of surfaces of contact presence of saturated vapour or even vapour anywhere near saturation must become filled with liquid held by surface

tension and not by adsorption. The same objection may be raised against the experiments with glass wool.

We have seen in Part I. that other data given in the literature are unreliable for similar reasons.

I have not studied in detail all the references cited by Gurvich as evidence of the large range of molecular forces, but the evidence of a contrary nature which has already accumulated is enough to make me feel confident that the large ranges are only apparent, and are due to secondary causes.

To obtain further information regarding the forces causing adsorption and the thickness of adsorbed films some experiments have been undertaken for me by Mr. Sweetser. We have used glass, mica, and platinum with very nearly plane surfaces, and have endeavoured to reduce the number of contacts between surfaces to a minimum. The pressures used were much below saturation and were usually less than 200 bars. It was found that at 100 bars' pressure the amount of oxygen, nitrogen, hydrogen, carbon monoxide, carbon dioxide, and argon adsorbed on glass or mica at room temperature were not measurable, although if 0.0002 of the surface had been covered by a layer one molecule deep it could have been readily

THE NATIONAL EXPOSITION

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INDUSTRIES, HELD IN NEW YORK.*
By THOMAS H. NORTON, Ph.D., Sc.D.
(Continued from p. 20).

detected. On cooling these surfaces to liquid air temperature the surfaces became covered with a monomolecular layer to the extent of 1 to 10 per cent, and at 100 bars' pressure they seemed nearly saturated. The relative amounts of different gases adsorbed were in the same order as the boiling points, showing that the forces involved in this adsorption were secondary valence forces such as those involved in the liquefaction of these gases. John Campbell and Co., Newark, N.J. With platinum surfaces the phenomena were totally THE company exhibited its "Amidine" series of direct different. Even at pressures below one bar the surface cotton colours, the "Kromeko" series of fast chrome adsorbed hydrogen, carbon monoxide, or oxygen imme dyes, the "Aceko series of acid colours, and the diately to form a layer covering the surface with a layer" Liberty" series of dyes for the hat trade. The various approximately one molecule (or atom) deep. These films intermediates employed in their manufacture were also could not be driven off by heating to 360°, but could be shown. made to displace one another. The surfaces were wholly saturated at a few bars' pressure, and no increase in adsorption could be noted by raising the pressure to 200 bars. These films are evidently held to the platinum by primary valence forces.

With the platinum at liquid air temperature the gases are first adsorbed by secondary valence forces, because when the temperature is raised to room temperature the gas first comes off the surface, and then at a temperature somewhat below room temperature goes back again on to In no case, however, was any adsorption noted which corresponded to a layer more than one molecule deep.

the surface.

It is, of course, possible in certain exceptional cases that more than one layer of molecules may be adsorbed on a surface. The tendency of molecules to evaporate from a second layer will in general be somewhat different (either greater or less) than from the surface of the liquid en masse. Such effects may be transmitted from layer to layer because of the orientation of the first layer of molecules, but in most liquids these effects are probably not transmitted in appreciably degree to more than one or two layers. Effects of this kind would be particularly noticeable with nearly saturated vapours.

From the foregoing considerations we may conclude that the "molecular forces" studied by Gurvich are really chemical forces according to all the tests given by him, and that their range of action is not greater than that of other chemical forces.

3. Gurvich's third objection to classing molecular forces as chemical is that they seem most active between similar rather than dissimilar bodies. This objection, however, arises merely from a confusion of secondary and primary

valence forces.

In the formation of compounds of the first order we generally find the most marked combining tendencies between strongly electronegative and electropositive elements, as for example between the alkali metals and the halogens. This tendency is most readily explained in terms of Lewis's theory.

On the other hand, all through chemistry we find evidence of reactions occurring between substances of similar type, especially where secondary valences are involved. This is shown by reactions between oxides, between halides, between metals, &c., and even by the reactions occurring between various organic compounds. Therefore, the fact that substances of similar character are usually mutually soluble, or that absorbing agents show a preference for chemically related substances is not to be looked upon as evidence that these phenomena differ in any essential respect from chemical phenomena, but merely as an indication that secondary rather than primary valence forces are involved.

As a final result of this discussion of Gurvich's paper we may conclude that the principles outlined in the beginning of the present paper are applicable to adsorption phenomena in general.

(In the remaining part of this paper surface tension, association, evaporation, freezing, melting, viscosity, solubility, and the internal structure of liquids will be briefly considered).

Niagara Alkali Co., Niagara Falls.

This company is engaged extensively in the electrolysis chlorine and bleach. It is now using large amounts of of salt, and markets the various soda products, as well as

chlorine in the manufacture of chlorobenzene, and exhibited this compound as well as dichlorobenzene. The latter was in the form of the commercial mixture of the The whole exhibit illustrated admirably the degree of isomers, as well as the pure ortho and para compounds. perfection attained in the development of the chlorine industry, as based upon electrolytic methods, and the use of the halogen in the production of coal-tar intermediates.

Hooker Electrochemical Co., Nigara Falls. This company also had a fine display of the products of It exhibited chlorothe soda and chlorine industry. benzene, o-dichlorobenzene, p-dichlorobenzene, benzyl chioride, benzyl alcohol, benzaldehyde, and benzoic acid. The manufacture of the last four compounds has been taken up quite recently. This company was one of the first to show the advantage of transforming coal-tar crudes into their chlorine derivatives at the points where chlorine is produced electrolytically.

John Merck and Co., New York.

In addition to a handsome display of alkaloidal, pharmaceutical, and general chemicals manufactured by this company in their works at Rahway, N.J., there were exhibited a large number of their current coal-tar products. These included the pure hydrocarbons, benzene, toluene, xylene and naphthalene, aniline, p-nitraniline, acetanilide, benzidine sulphate, nitro-benzene, m-dinitro benzene, mphenylene diamine, p-phenylene diamine, phenol, o-nitrophenol, p-nitrophenol, p-amidophenol, phenolphthalein, resorcin, hydroquinone, sulphocarbolates, 3-naphthol benzoate, bismuth 8-naphthol, salicylic acid, methyl salicylate, acetylsalicylic acid, acetphenetidine, salol, aurine. induline, and nigrosine- The exhibit was instructive, and revealed the wide range of activity of this long-established firm. Its coal-tar products are chiefly for medicinal and photographic use.

H. A. Metz Laboratories, Inc., Brooklyn. The exhibit of this recently orgainsed company contained an admirable display of its synthetic medicinals, salvarsan, novacain, and anæsthesin. All of the intermediate steps in the production of salvarsans from aniline and arsenic acid were shown in carefully prepared samples. The establishment of the manufacture of this important synthetic drug on American soil is one of the leading leatures of the year's progress.

A similar vacuum dryer, in full operation, and an autoclave, holding 200 gallons, and working under 1000 lbs. pressure, excited much interest, as did a jacketted receiver, an enormous nitrator, a capacious fusion kettle, and a denitrator. There were numerous types of evaporators, for rapid circulation, for high concentration, for crystallisation, with horizontal and vertical tubes, &c.

Among other forms of chemical apparatus shown by installation or plans, were :-Acid eggs, acid concentrating apparatus, 8-naphthol plant, caustic flaking machines, General Bakelite Co., New York. caustic soda plant,causticising apparatus, reflux condensers, Bakelite was shown in a great variety of forms, intended crystallisers for TNT, ammonium nitrate, &c., vacuum for the most diverse usages, but chiefly in connection with crystallisers, expansion tanks, impregnating apparatus, electrical insulation. It is the trade name of a unique nitric acid retorts and condensers, pumps of many types: synthetic substance, oxy-benzyl-methylen glycol-anny-recovery systems for sulphuric and nitric acids, retorts dride, discovered by Dr. L. H. Baekeland, after a series (shell type), salt filters, stills for aniline, s-naphthol, of brilliant research experiments, and is a condensation phenol, &c., and sulphonators. product of phenol and formaldehyde. In its pure form it is a hard amber-like substance of pronounced chemical inertness. It combines high mechanical and dielectric strength with marked heat resistance, and can be moulded with great accuracy and fine finish It is also non-hygroscopic, impervious to water, steam, oils, and most chemicals; has excellent weathering qualities, and will not warp, soften, swell, or deteriorate with age.

This unusual combination of properries has rendered bakelite available for a great number of purposes. An especial degree of interest is attached to it as one of the few coal-tar products discovered in this country and introduced into general technical use.

The Stamford Extract Manufacturing Co., Stamford,
Conn.

The successor to the old Stamford Manufacturing Co. displayed fine samples of the different dye woods, as well as of quebracho, and the different extracts obtained from them in its large works. There were numerous examples of the results secured with them in dyeing. The hematin crystals were especially noteworthy.

The Obex Co., Marietta, O.

This firm is one of the latest to enter upon the production of dye-wood extracts. It showed particularly fine cross-sections of Brazil wood, fustic, logwood, and Osage orange, and a complete collection of the various extracts. The firm is planning to enter also upon the production of synthetic dyes.

Imperial Colour Works, Glens Falls, N.Y. Exhibits were made of lakes and toners made from p nitraniline and from toluidine, in company with a variety of dry and puip colours. There was also a good display of vegetable dyes manufactured in the plant of John H. Heald and Co., Lynchburg, Va. It included extracts of logwood, fustic, and hypernic, hematine crystals, fustic crystals, wool and leather yellows.

The Buffalo Foundry and Machine Co., Buffalo, N.Y. The exhibit of this company was the most imposing and the most extensive in the Exposition, occupying the entire western end of the main floor. It revealed in a remarkable way the complexity of the mechanism now employed in the production of chemicals and dye-stuffs, and the contributions of mechanical engineering in this field. The company has been an important factor in furthering the rapid development of our domestic coal-tar chemical industry, by devising the requisite apparatus, and by rapidly supplying it in great quantities to newly organised

firms.

The pièce de resistance at the Exposition was certainly its vast vacuum drum dryer, weighing 50 tons, with its two-stage dry pump, surface condenser and dust collector. One of the greatest successes in American foundry work is represented by the huge casing of the dryer, cast in a single piece.

A large staff of engineers and chemists were in attendance, and the decorations and settings for the It testified in a striking exhibit were in admirable taste. manner to the exeeptional claims which the chemical industry now makes upon the mechanical engineer.

7. P. Devine Co., Buffalo, N.Y.

A handsome exhibit of vacuum pumps, condensers, drying apparatus, and high pressure cast-steel autoclaves, such as are now used extensively in making coal-tar intermediates and finished products.

The Pfaundler Co., Rochester, N.Y.

There was a fine display of the different forms of chemical apparatus, lined with resistant enamel, now required in variety by the manufacturers of coal-tar products, when dealing with strong acids. The specialities of this firm are highly appreciated in other countries, and a branch factory was maintained in Germany prior to the war.

Elyria Enamelled Products Co., Elyria, Ohio.

The exhibit included a number of pieces of chemical apparatus lined with enamel. This firm specialises in the production of enamelled tubes.

Sowers Manufacturing Co., Buffalo.
An excellent display of steam-jacketted kettles, mixers,
vacuum-pans, &c.

Shriver and Co., Harrison, N.J.
Various types of filter-presses.

United Filters Corporation, Brooklyn.
An instructive exhibit of new types of filters in constant
operation.

Kelly Filter Press Co., Salt Lake City.
Presses were shown in regular operation.

Arthur D. Little, Inc., Boston.

This firm is doing fine work as consulting and con struction chemical engineers, and exhibited interesting evidences of the character of the work accomplished by its staff of sixty, occupying a handsome buiiding at Cambridge, Mass.

Civic, State, and Railroad Exhibits.

A striking feature were the extensive collective exhibits of states, cities, railroad companies, and public organisations. Noteworthy in this connection were the large and instructive displays made by Louisiana and by Texas, as well as by the Southern R. R. system, the Carolina, Clinchfield, and Ohio R.R., the Central of Georgia R.R., the Nashville, Chattanooga, and St. Louis R.R., and the Norfolk and Western R.R. of Virginia. The south is making a vigorous effort to direct attention to the vast undeveloped wealth in its territory, awaiting the advent of chemical industry. The great variety of samples and