can only assist. It cannot be, and does not aim at becoming, more than an accessory. Let us ake our minds quite clear on this point. Interest does NOT mean interference.

We are pleased to reproduce the introductory chapter by the Right Hon. F. G. KELLAWAY, M.P. THE NEED FOR GOVERNMENT ASSISTANCE TO COMMERCE.

In looking beyond the immediate present, the most casual observer is forced to the conclusion that the fiercest struggle for foreign trade since our merchant adventurers first set sail will soon engage the whole fabric of British industry. For us, and for most other nations, the only way of replenishing the national coffers, and replacing that vast wealth which has been expended and destroyed, is to increase our overseas trade.

The more quickly we develop our export trade, and so strengthen our exchanges, the sooner we shall lighten the burden of taxation, and this, of necessity, is of great personal interest to each one of us. If we look at the present-day position geographically and commercially, we see how the very existence of this country depends upon its

overseas trade.

The United Kingdom is exceptionally dependent upon outside sources for foodstuffs and for raw material for its industries. We must sell extensively abroad in order to be able to purchase our requirements from abroad. In other words, we stand or fall by our export trade.

Before the war, 78 per cent of the wheat and 40 per cent of the meat for home consumption

came from overseas. When we take raw materials into consideration as well, we find that nearly 80 per cent of our imports comprised commodities which we must import.

This will give some idea of the extent to which we are dependent upon other countries, and any reduction of our imports through inability to pay by our exports would materially and adversely affect the prosperity of the community as a whole. Communications and transport are of the first importance to a successful development both of home industry and overseas trade; but of scarcely less importance is the collection and dissemination of commercial information. Every trader will recognise at once the urgent necessity of knowing what his competitors are doing, how matters relating to overseas markets stand, and what are the conditions and prospects in them for our overseas trade. In keeping himself fully posted as to conditions abroad and as to openings for business, the individual initiative of the trader counts before anything else. The Government

Since Government interest in commercial matters is recognised and felt to be a national necessity by every other great Power, surely we, in view of our insular position and vital dependence upon outside sources for supplies of food and raw materials, have the greater need for Government assistance. It was expressly with the object of giving this help that the Department of Overseas Trade was instituted in the summer of 1917, and there is already ample evidence that its alliance with British traders has directly contributed to the expansion of British export trade.

The more frequently British traders have recourse to the Department, the more useful it will be.

Any firm in the United Kingdom engaged in the export of British goods can make use of the Department's services free of charge, and no preferential treatment is made by the Department between the large and small firm, between the manufacturer and the merchant.

The work, which has issued from the laboratory of the Elektro Osmose Aktiengesellschaft, still remains the largest contribution to this class of work. Undoubtedly the Schwerin patents applied to the purification of clay form one of the most interesting practical adaptations of the complicated physical laws dealing with colloids.

The history of the development may be described briefly as follows:

First the discovery that suspensions of many clays could be so treated by a direct current of electricity as to bring about the deposition of the clay in a more or less dry state on a negative pole. It was found that all clays did not react and a second series of patents deal with the possibility of increasing reactivity of the clay particles to the electric current by adding traces of suitable electrolytes which were absorbed by the clay. tion of suitable electrolytes there were clays which Further work showed that even with the addiwere not amenable to electrical separation or at any rate not in a sufficiently pronounced degree to render the process commercially applicable. A third series of patents was taken out claiming the use of added colloidal substances which would be adsorbed by the clay, which colloidal substances

*A General Discussion before the Faraday Society and the Physical Society of London, 25th October, 1920.

were then capable of adsorbing the necessary electrolytes, and for this purpose such bodies as sili cate of soda, humic acid (Casseler brown earth; and the like were employed. Count Schwerin was one of the first to realise the possibility of apply ing the comparatively new scientific discoveries relating to colloids to industrial purposes. So far as my knowledge goes, he was the first man to recommend the addition of electrolytes, with or without other colloids, to clay suspensions, with the object of converting the clay into the sol condition so that the sedimentation of the heavier impurities might take place. It is impossible by mixing a plastic clay with even a large amount of water to separate the bulk of the impurities with out losing a lot of clay substance and without the use of an excessive amount of water. The free silica which is always present in clay is surrounded by clay in the gel form and the separa tion of this clay from the particle only takes place when suitable electrolytes are added so that the clay is peptised and separated from the silica.

The osmose machine applied to the separation of

the suspended particles is an interesting example of the application of comparatively recent physical-chemical laws. In the preparation of the clav we make use of the laws of selective adsorption, of the influence of adsorbed colloids and finally of the directive effect of an electric current on a suspension of particles in the sol condition. On the anode of the osmose machine the negatively charged particles are deposited and the moment a film of these exists over the anode, brought about by cataphoresis, electro endosmose comes into action and the water in and around the clay is electrically driven through the capillary spaces resulting from the close contact of the clay particles deposited on the anode. It is interesting to note that the amount of moisture remaining in the clay attached to the anode is intimately related to the physical nature of the clay substance. If china clay is being worked upon it will be found that if sedimentation is carried out to such extent that only 50 per cent of the clay substance remains in suspension, so that only the finer particles of the clay remain, such a suspension treated on the osmose machine will give a product containing approximately 28/32 per cent of water. If the china clay which has settled out be now remixed with water and passed through the osmose machine-that is, if we make use of the coarser clay particles only-the osmose machine will yield a product containing 35/40 per cent of water. On the other hand, if similar experiments be carried out with a very plastic ball clay having much finer particles in the sol suspension, the osmose machine may deliver a product containing as little as 18 per cent of water. It would appear as though the percentage of water in the clay delivered from the osmose machine were due in some measure to the fineness of the state of division in the sol state and to some extent also it is a measure of the plasticity.

In treating a very pure specimen of a wellwashed English china clay by the osmose process, it has been found possible to deposit as much as 6833 kilogrms, of dry clay substance with 118 kilowatt hours of current when working at 50 volts pressure.

It is interesting to regard this deposition of clay by direct electric current as though we were dealing with the deposition of copper from a solution

of one of its salts. On the basis of the figures given above, we should have to assume that the quivalent weight of china clay was of the order of 700,000 and that where a given current would deposit 1 grm, of hydrogen or 31 grms. of copper, it would deposit 700,000 grms. of clay. Needless to remark, these figures can only be obtained when working with very pure clay and with water of very low conductivity.

It has been stated that the electro osmotic process does not bring about any purification of the clay material in the actual osmose machine, but, whatever may be the position theoretically, the fact remains that in practice such a purification is brought about, as has been proved beyond all doubt at the laboratory of the Osmosis Company, Limited, by Mr. Lawrie, when working on tons of china clays and ball clays.

Peat.

The application of the electro-osmose filter press to colloidal peat suspensions results in the removal of large quantities of water at a compara

tively low cost in fuel; thus hydraulically mined peat, containing only 5 parts of dry peat substance in 100 parts of suspension, results in the removal of 85 parts of water from the 100 parts of mixture, with an expenditure of current which can be produced by the consumption of one-sixth of the resultant fuel. The ultimate drying of the product from the filter press containing 1 part of peat to 2 parts of water is comparatively simple, but the difficulties attached to the use of the process are more largely mechanical. Unfortunately peat is generally found in comparatively thin layers, and owing to the small percentage of dry substance contained in the peat, the osmose plant would soon be far distant from the point where the fuel was being worked. It is obvious that the process lends itself particularly to application in countries where water-power is available for producing the necessary electricity.

Colloidal Silica.

By passing an electric current through silicate of soda solutions it is possible to drive out the soda and leave the silicic acid behind, but this can only take place if diaphragms are employed which will permit of the soda ions passing out of the silicate of soda solution and will not permit of backwards way diffusion into the inner chamber. Years of experiments have resulted in the development of such diaphragms, and it is now possible to produce silica solutions up to 30 per cent in strength, but the stability of these solutions diminishes as the concentration increases. It is interesting to note that the stability of these silica solutions has been found to increase with each step in progress which has been made, resulting in the more complete removal of the sodium salts. These silicic acid solutions of 5/10 per cent strength have been largely used on the Continent for therapeutical purposes, and the strong solutions after polymerisation result in the formation of a gel, which, on drying, produces an inert highly electro-negative finely divided colloidal gel, which has proved to have extraordinary properties as an adsorbent for use on wounds. In the Third Report on Colloid Chemistry, p. 123, there is a reference to a statement by W. Ostwald "that fresh colloids (particularly silica) will pass through a membrane, but after keeping a few days they will not pass through." It adds, "there is no

connection between the rate of diffusion through the membrane and the molecular weight." It has been found that the silicic acid solution produced by the electro-osmose process, at the moment of its preparation, has a molecular weight corresponding to the formula H,SiO,, and that the molecular weight increases steadily with the time, until a 10 per cent solution, after about 6 weeks, the molecular weight has reached something in the order of 60-80,000, and obvious separation takes place. If a 10 per cent solution of silicic acid be kept in a vessel lined with paraffin wax, it is possible, by means of conductivity experiments, to determine the age of the preparation to within a few hours. It would seem likely, therefore, that the ability of new solutions to diffuse through a diaphragm is directly and closely connected with the molecular weight. No doubt Ostwald's less pure solutions polymerised to such an extent in a few days that they could no longer pass through a diaphragm.

Tanning.

It would appear that a very great simplification has taken place in the plant now used for electric tannage of skins. Two factories in Germany are at present employing the process, and the chief claim made is that it permits of the utilisation of very dilute tanning liquors, with complete utilisation of the tanning material. It is further claimed that experiments have shown that it is preferable to complete the tanning for two or three days in the ordinary way in strong liquors, and that the current consumption is thereby reduced from 20-25 kilowatt hours per square metre of hide; when complete electrical tanning is employed, to 6 or 7 kilowatt hours per square metre; when finishing in strong liquors is employed. Here, again, progress has resulted entirely from the discovery of suitable membranes for the enclosing of the anode and cathode.

Ore Separation.

It has been found that if a finely ground ore be suspended in water, that in many cases it is possible to add traces of electrolyte which are selectively adsorbed. If such finely ground ore be allowed to fall through a column of water to which has been added the necessary quantity of suitable electrolyte, and if a current be passed through the water at right angles to the path of the falling particles, the charged particles are drawn on one side and fall into separate receptacles, bringing about concentration of the ore.

Iron ores occurring in clay deposits have been concentrated by the removal of the clay substance on the lines above described.

Anti-Diphtheritic Serums.

It has been found that the anti-toxin contained in the blood serum of a horse is combined, for the most part, with the para-globulin, very little being combined with eu-globulin, and practically none with the fibrinogen. It has proved possible by using suitable diaphragms to separate from the anti-diphtheritic serum of the horse a pure paraglobulin containing the bulk of the anti-toxin previously present in the serum. Such anti-diphtheritic globulin is free from amino acids, and from the decomposition products of the albumen bodies such as albumose and petones, and bodies

containing ferments such as katalase, enzymes, and the like. Furthermore, it is claimed that the anti-diphtheritic product so prepared is free from toxon. It has been urged that anti-diphtheritic serum of a horse may, and probably does, contain toxins which have been combined in a weak way with anti-toxins, and that these compounds may split up in the human body with the setting free of toxins which may lead to, and be the cause of, the dangerous secondary symptoms which so frequently occur after serum injection. It is claimed that the electro-osmose process separates the toxon as such, as well as splitting the compound of toxin and anti-toxin with separation of the toxin. The resulting pure anti-toxin para-globulin has concentration six to ten times that of the best horse

serum.

Gelatine.

By the use of diaphragms very similar to those employed for the separation of the constituents in serum, it has proved possible to prepare exceedingly pure gelatins from low grade gelatin, and even from glue. These gelatines are so pure that a 5 per cent solution may be kept for weeks or months without any bacterial growth occurring therein, owing to the fact that the whole of the food material which is necessary for bacterial growth has been so entirely removed. Such gelatine is being prepared in this country, and is being tested for photographic and other purposes.

The Removal of Oil from Water.

The electrical methods which are employed for the removal of oil from watery emulsions is really an application of cataphoresis. The oil globules are charged by adsorption of the inorganic salts present in traces, and pass to the anode.

Dewatering of Oils. It is well known that many tars produced by distillation and many natural paraffin oils contain water in a state of emulsion which is very difficult to separate. Just as the application of direct current electricity has for some time been employed as above stated for the separation of oil emulsions from water, so similar electrical methods are used for the removal of the water particles forming the disperse phase in oil as a continuous phase. This application is very largely used in the Californian oilfields.

are now occupied by the high-temperature ores. Any other hypothesis would be illogical, and we have good reason for believing it to be the same siliceous medium that carried them all.

Tin and wolfram-bearing veins, however, are not all of this multiple type. Some extend in a single line for many thousands of feet parallel to the axis of the mother batholith. It is evident that there is some difference in the cause of fissuring in the two types.

The writer has ascribed the origin of the multiple type to the percolation of meteoric water down to the magma at these points, and no other explanation so far offered seems capable of accounting for the phenomena displayed by this type.

The long single vein parallel to the axis of the batholith may be accepted as the more normal, for this is what we should expect as the result of ejection of mother-liquor along the ridge of a batholith. Few of these exist in Burma, but they are characterised by having been reopened several times, and contain molybdenite, wolfram, cassiterite, scheelite, bismuthinite, chalcopyrite, pyrites, pyrrhotite, blende, galena, and stibnite, besides mica and fluorite with the high-temeperature minerals and quartz which accompanies them all. In one we have "micropegmatitic" growth of quartz in pyrrhotite, which seems to indicate that a pyrrhotite-silicic acid eutectic is capable of existing.

It is believed that much more information of a definite nature concerning the cause of fissuring, as well as the conditions of filling of veins, is to be obtained by patient study of the high-temperature deposits rather than of any others.

The Upward Succession of Ore Minerals. Lindren classifies primary ores as follows :— 1. High-temperature deposits.

I.

2. Deposits formed at intermediate depths. Deposits formed near the surface.

3.

This classification is a very useful one, but its author probably attaches undue importance to the presence of accessory minerals. As an example chalcopyrite-tourmaline deposits are regarded as high-temperature, whereas chalcopyrite without tourmaline is placed among deposits formed at intermediate depths.

It would be preferable, perhaps, to adopt a classification strictly according to relative temperature of origin without reference to depth, since temperature is of much greater importance in the matter of ore deposition than distance from the surface. In the present state of our knowledge there is nothing definite in either. Both have altered by a varying amount since Silurian or even Tertiary days.

In place of (2) and (3) above, "Intermediate Temperature Deposits" and "Low Temperature Deposits" are suggested.

Consideration of the actual temperature limits of the three classes would be hopeless with the data at present available, and exact knowledge of such, even if attainable, probably would not be of great economic importance.

Regarding the upward succession of ores, lack of space prevents our mentioning any but the most important ones. We shall deal only with ore minerals occurring in veins deposited therein directly by magmatic solutions, and we assume

them to be carried in silicic acid. We also assume that an open fissure exists up which solutions pass. Pneumatolysis, in this connection, is entirely rejected.

At its opening the temperature in the fissure immediately above the batholith is abnormally high, but at no great distance upward it is normal and falls at the normal rate for the district as the surface is approached. After the first inrush, the flow of ore-bearing liquid in the fissure is probably slow, and at all points its temperature is a little higher than that of the walls, heat being transferred from the former to the latter. As the flow is slow and the volume of wall-rock enormous, no very great degree of heating of the latter is possible. The liquid on leaving the batholith carries, say, tin oxide and chalcopyrite in solution, its temperature falls as it passes upward, and at a certain point cassiterite commences to deposit and continues to do so upward until all the tin in solution is exhausted. This will take place when the liquid has fallen to a temperature at which it can no longer hold tin in solution. The temperatures at the two points which are the lower and upper limits of tin deposition give the temperature range of the formation of cassiterite. The same liquid carries chalcopyrite and some iron disulphide as well. Along with cassiterite some pyrites is usually deposited-this mineral is peculiar in the respect that it is deposited in veins at all temperatures-high, intermediate, and low. No chalcopyrite was deposited with the cassiterite below, but near its upper limit chalcopyrite commences to develop and continues until a point is reached where the temperature of the liquid no longer permits it to hold copper in solution. Here again we have a range of temperature within which chalcopyrite deposits; the hotter limit is nearly coincident with the cooler limit for tin, but the two may overlap slightly.

It is evident that the local temperature gradient in the strata is the principal factor in determining the vertical distance in the vein through which gradient the greater the range or persistence in any particular ore will be deposited, the lower this

depth.

The average gradient is about 1° C. per 100ft. of depth. Morro Velho gold mine in Brazil provides an extreme example of persistence in depth (over 6,400ft.), and there the temperature increase averages only 1° C. per 140ft. of descent.

chalcopyrite rarely amounts to as much as 2000ft., The vertical range in veins of such ores as and, taking the temperature gradient at normal, this distance represents a temperature range of only 20° C. From this we are forced to conclude that the temperature limits within which any particular ore is developed are very narrow.

It seems likely that there is for each metal a definite maximum and minimum temperature between which its deposition as a primary ore takes place; above the maximum it remains in solution entirely, and below the minimum the primary solvent cannot retain it.

There seems a possibility that this temperature range may be modified to a slight extent (probably varying in the case of each metal) by pressure. Such modification is regarded, however, as not amounting to more that a few degrees of temperature. Since the variation in temperature involved