434
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
foreseen in hlr. Garvan’s statement, though he is not a chemist. These other things must of course be done and done well, but, oh, my friends, the chemistry of the body is too little known. Think about the fact that the body is a mass of chemical reactions, which when normal mean life, and health, and happiness, but when abnormal signify disease and misery and unhappiness. Yet these are simply chemical changes. This country is spending millions of dollars for drugs on the bare chance that they may happen to be the right thing. We must get these matters on a scientific basis. We must get deeper into the knowledge of how these drugs act. It will take time, and a tremendous amount of research, but surely the goal of American chemists is a noble one, if it can start toward the attainment of the alleviation of the suffering of America. What lies beyond that we do not know, perhaps a prolongation of the average life of mankind, perhaps more happiness through life. There is something deeper in our work than mere commercialism. I am talking about industrial chemistry now, too. I don’t know exactly what it is. I can’t yet get my thoughts clear about it, but down in my heart I believe that when our people thoroughly understand what we are trying to do, and are thoroughly sympathetic with our aims and aspirations, when full opportunity is given for the highest energy and effort of American chemists, somewhere in that science to which we devote our lives will be found that which is u p l i f w to life in every way. n
-
COLLOID SYMPOSIUM SOME PRACTICAL APPLICATIONS OF COLLOIDAL CHEMISTRY By Jerome Alexander RIDGEFIELD, CONNECTICUT “COLLOIDAL”
FUEL
What promises to be one of the most far-reaching advances made under the stress of the recent war, when necessity literally was the mother of invention, is the discovery that by means of a suitable “fixateur” or peptizing agent and suitable treatment, very large percentages of cheap tars and finely powdered coal waste may be dispersed in fuel oil with a sufficient degree of permanence to enable the mixture to be stored, piped, atomized, and burned practically like fuel oil itself. Since this new composite fuel will a t one stroke relieve the drain on the earth’s rapidly diminishing stores of petroleum, as well as lead to the efficient utilization of all kinds of coal waste (culm, screenings, dust), inferior fuels (peat, lignite), and even cellulose waste (slabs, sawdust), it may be hailed as a powerful factor in the conservation of our natural resources and a lasting benefit to mankind. Realizing the vital importance of the Allies’ oil supply in the conduct of naval, military, and manufacturing operations, the German submarines bent every effort to destroy tankers; and Marshal Foch is said to have cabled America: “If you don’t keep up your petroleum service, we shall lose the war.” While the Allies’ navies were dealing with this peril in a most decisive fashion, Lindon W. Bates, head of the Engineering Committee of the Submarine Defense Association, with the assistance in laboratory matters of Dr. S. E. Sheppard and other chemists of the Eastman Kodak Laboratory, courteously opened to him, developed a colloidal fuel, which, by practically doubling the usefulness of every oil cargo, would have of itself materially assisted the defeat of the Hun efforts. Coal or other combustible solid is prepared for dispersion by being pulverized so that about 95 per cent passes through a roo-mesh, and 85 per cent through a zoo-mesh screen. This of course means that by far the greatest weight is in particles hundreds and thousands of times larger than colloidal dimensions. But we should remember that the violent motion of the colloidal
Vol.
12,
NQ.5
particles causes the Brownian movement of much larger particles, as is the case in milk where the fat globules can be seen in the ultramicroscope oscillating about under the ceaseless bombardment of the casein ultramicrons. It has been found that a fluid fuel may be made containing as much as 40 per cent by weight of powdered coal, and mobile pastes containing up to about 75 per cent; and mobile gels may be made both from the liquid and the pastes. The exact nature of the fixateur is withheld pending the issuance of patents here or abroad, but it is stated that ordinarily between 0.5 and 1.5 per cent of the essential component of the fixateur is used, whereas about 0.1per cent exercises a noticeable influence. The amount is determined by the nature of the mixture, the components, and the degree of permanence desired. The bulk of the particles does not begin to settle until the period of “life” has passed, the colloidal fuel having a limited “life” which may be regulated to meet requirements-days for power plants, weeks and months for ocean-going vessels and central storage stations. Heat and agitation revivify the liquid fuel, and the paste form may be kept for years. Being heavier than oil or even water, colloidal fuel compresses in a unit volume the maximum thermal value, thus economizing storage space; and it may be stored under and extinguished by water, thus avoiding evaporation, deterioration, and fire risk. Its operative efficiency is high, for when sprayed into the hot fire box the oil-permeated particles of carbonaceous matter are still further atomized by the sudden gasification of their imbibed oil. It possesses the advantages of fuel oil over coal-absence of smoke, dust, and ash, practical elimination of labor in loading into storage space and in firing, with resultant saving in time for “coaling” and for raising steam. As with oil, a protective smoke screen may readily be produced by over-firing, and the fire is subject to instant control. SMOKES
While it is an ancient principle of strategy to attack an enemy under cover of natural fog or mist, the recent war resulted in an enormous development of artificial smokes as aids to naval and military offensive and defensive operations. Like the cuttlefish, steamers strove to escape pursuing submarines in colloidal clouds of their own making, and soldiers crept to the attack under the protection of a smoke barrage. In the air, nature’s own clouds were favorite hiding places for aeroplanes and dirigibles, and the latter (especially Zeppelins) often produced their own concealing clouds. In times of peace the treatment of smokes and fumes is mostly confined to their coagulation by the Cottrell process, by which sulfuric acid mist or zinc oxide fumes have been collected as part of the ordinary course of operations, and by which injurious industrial dusts, i. e., smelter and cement fumes, have been converted into sources of profit. There is, however, one case of the commercial production and utilization of smoke that possesses features of interest-the use of the so-called “smudge-pot.’’ Smudge-pots are burned in orchards, especially in spring or early summer, when weather conditions indicate that the tender blossoms or fruit are apt to be injured by frost. The heat emitted by the pots is apparently a small factor, their efficacy being due to the dense clouds of smoke evolved by the burning smudge oil. This remedy is of course useless in very cold weather, and serves only to prevent what agriculturists term a light frost, which has for its precursors a still, clear atmosphere, and a temperature approximating the freezing point. No frost of this kind occurs on cloudy or windy nights. The freezing process, in the absence of smoke, seems to proceed as follows: as the temperature drops, moisture deposits like dew upon leaves, fruit, buds, and other surfaces furnishing nuclei, and congeals into ice crystals or “frost,” when the slight heat thus set free by condensation is dissipated into the surrounding cold atmosphere, the freezing being also facilitated by the evapora-
May, 1920
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
tion of part of the deposited water. The smoke, however, furnishes throughout the entire lower atmosphere innumerable nuclei for the deposition of moisture, and the slight but widely distributed heat thus liberated is sufficient to carry the temperature, locally, above the freezing point. Moisture on such small nuclei does not readily evaporate, and the smoke fog furthermore forms a kind of protective blanket which reflects terrestrial heat and prevents its dissipation. SHOWER-PROOFING O F FABRICS
Ordinary textile fabrics are readily wet by rain, but if coated with a surface film of wax or the like (aluminum stearate), the falling droplets roll off “like water off a duck’s back.” This water-proofing effect is readily understood if we consider the interfacial surface tensions involved : I-Surface 2-Surface 3-Surface
tension water/air, denoted b y oWA tension water/fabric, denoted by oWF tension air/fabric, denoted by uAF
Practically speaking, the surface attraction of the untreated fabric for water is so great (i. e., uWF is so small’) that both the surface film or skin of the raindrop and the air film on the fabric are burst; the raindrop spreads itself out on the fabric, and is absorbed into its pores. That is, wetting occurs if uWF uWF uAF. In the case of the treated fabric, aWF is very much increased; becoming in fact the surface tension water/wax, for surface tension is only skin-deep. Therefore u W F > U W A uAF or uWAuWO uAO 75 23 33 (approximate values).
+
This yields air bubbles with a more or less stable surface film,
i. e., a foam or froth. This film is miscible with the oil film on the sulfide, although not necessarily identical with it, because there may be a separation of the constituents of the oil by 2ifferential adsorption. The oiled sulfide particles therefore act like oil, and. distributing themselves a t the interface water/ air, are attached to the air bubbles and lifted to the upper froth layer, if they are not too heavy or are not knocked off. In the foregoing no account has been taken of complicating factors which are always present and while space will not 1 It should be borne in mind t h a t t h e surface tension decreases, as t h e attraction between the phases increases. In fact, when the positive surface tension i n a two-phase system becomes zero, solution may take place.
The consumption of petroleum is increasing so rapidly that a material decrease in the supply, if not actual exhaustion, lurks in the not far distant future. W. B. Hardy in a trenchant paper3 has shown that we may with confidence look to colloid chemistry to aid us in finding the lubricants of the future. Glass surfaces selectively adsorb from the air rather more or the atmospheric impurities than of the elementary gases and water vapor, yielding a film about I p p ( I X 1 0 - 7 cm.) thick, which Lord Rayleigh termed “grease” because it has the general properties of an 0i1.4 For this reason a new or raw glass surface has different mechanical properties than a satisfied or neutral surface. It is not possible t o get a raw surfaces of glass. One cannot cleave glass; but the “grease” film may be renioved by rubbing the surface under water. Soaking is insufficient; actual vigorous 1 Mechanical agitation and temperature exercise considerahle influence. Callow estimated t h a t with four different oils, three oil percentages, two pulp densities, and two temperature changes, there are about 60,000 possible different combinations of conditions. 2 T h e layer of tiny adhering ore particles forms an armadillo-like armor about the air bubbles, which t o a large extent protects them from coalescence and destruction. 8 J . SOC.Chem. Ind., 38 (1919), 7 t . 4 This adsorbed layer of “grease” tends t o make pipettes and burettes deliver inaccurately, so analysts remove it by oxidation with bichromate. 5 R a w surfaces are readily made by cleaving mica, and if immediately p u t together again, they adhere so strongly t h a t they withstand a powerful lateral pull, and usually tear t h e surface when finally separated. LJ. A , ]
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
436
rubbing is necessary, pxekrably with the finger tips until a peculiar clinging feeling is produced: the same which is felt when the edge of a finger bowl is rubbed so as to give out a musical note. A surface cleaned in this way has some remarkable mechanical properties, the most striking being that two cleaned surfaces seize when pressed together with a relatively small force. This may be dernonstrated very simply by measuring the tangential force needed to produce slipping. That true seizing occurs is prowd by the ‘tearing of the surfaces which takes place in the act of slipping. The function of lubTkants is to keep the applied surfaces in the neutral condition by maintaining a “grease” film on each. Not all fluids, however, can act in this sense as lubricants for any particular surface such as that of glass. Water, ether, alcohol, benzene, and strong ammonia are apparently entirely incapable of maintaining a lubricating film on glass. Seizing occurs just as readily when they are present as it does with cleaned surfaces. Glycerol differs from the fluids mentioned above in the fact that though it wjll not maintain a lubricating film it does prevent seizing when present in excess. For instance, the maximal tangential force which a pair of cleaned surfaces would support without slipping was measured in grams, 5 5 , Flooding the surfaces with water, benzene, alcohol, etc., left this value unchanged. When a film of glycerol was deposited on the surfaces the force still stood a t 5 5 , but i t fell to 9 when the surfaces were fully flooded with glycerol. The expression “film” used above denotes a layer of fluid on the solid surface of the order IO-’ cm. in thickness. With a true lubricant ‘the facility for slipping is maximal when a layer of such excessive tenuity separates the solid faces and nothing is gained by increasing the thickness of the layer. Thus with castor oil the weight required just to start one face of glass slipping over another was I O g. when only the invisible film of fluid mentioned above was present, and it was still I O g. when the surfaces were flooded with oil. Some fluids indeed seem to lubricate better in thin than in thick layers; that is to say, to act in the contrary way to glycerol. Acids as a class behave in this way, the solid faces again being of glass. PULL IN GRAMS
..
FILM
FI,OODED
Acetic a c i d . . , , . . . . . . 40 Sulfuric acid ... . . 37
E.
If this result can be fully substantiated it will be an important and striking physical fact likely to throw much light upon the process of lubrication. One broad conclusion emerges from thes’e facts, namely, that lubrication depends wholly upon the chemical constitution of a fluid, and the fact that the true lubricant is able to render slipping easy when a film of only about one molecule deep is present on the solid faces, suggests that the true lubricant is always a fluid which is adsorbed by the solid face. If this be so, then the problem of lubrication is merely a special problem of colloid physics. Some solids, notably graphite, are lubricants themselves. But the chief function of graphite seems to be as an aid to lubrication by oil. The graphite is disintegrated in the bearing and besides filling up relatively large imperfections, its colloidal particles are adsorbed by the iron, forming in reality a graphite surface which has a lower surface tension against oil than iron has. Practically this means that the oil film adheres more strongly to the graphitized surface and therefore needs greater force or pressure to’break it down; i. e., the bearing will stand greater speed and pressure. Acheson’s “oildag” consists of a paste of colloidal graphite dispersed in oil. A small percentage is mixed with the ldbricating oil and feeds with it through the finest orifices. “Aquadag” is ’the corresponding water-soluble product, stabilized with tannin. CERAMIC PROCESSES ASSOCIATED PHENOMENA1
WITH COLLOID
By A. V. Bleininger PITTSBURGH, PSNNSYLVANIA
This paper is intended to present some of the aspects of colloid chemistry which have a bearing upon the technology of clays. Within the scope of this contribution it is not possible to consider 1 Published
by permission of the Director of the Bureau of Standards.
12,
No. 5
the subject a t all completely and attention can be called only to certain of the more important topics. Clays are mixtures of finely divided hydrated aluminum silicates with granular matter such as quartz, feldspar, mica, etc. These represent all grades of subdivision, from the coarsest t o the finest. The property of plasticity, the ability of the substance to be molded when admixed with water and to retain the shape imparted to it, is to be attributed to the dispersed state of the aluminum silicates, principally A120a.zSi02.zH20,known under the general term of clay substance. The pure type mineral, known as kaolinite, sometimes found in crystalline form, rarely occurs in clays but has usually been reduced to particles apparently devoid of crystalline structure, of the magnitude of 5.u or smaller, admixed with colloidal material like ferric oxide and organic matter and frequently strained by absorbed salts. Clays are not necessarily plastic in the natural state but may have been indurated by pressure or heat, or set through other agencies so they cannot be made plastic without the aid of grinding. This is particularly the case with materials consisting of hydrated silicates other than A120&XO2.zH20, such as halloysite, pyrophylite, indianite, etc. The colloidal character of clays was recognized as early as 1874 by Schloesing’ and later more definitely by Rohland2 and C ~ s h m a n and , ~ it was agreed that a clay is very plastic, fat or sticky when the colloid matter is in excess or sandy; weak or non-plastic if the granular matter predominates. The colloidal characteristics of clays are substantiated most effectively by ultramicroscopic examination. Recent work of Jerome Alexander4 has shown that the Brownian movement is observed with practically every type of clay suspended in water, varying from the rapid motion of the finest particles to the more sluggish one of the larger particles or aggregates or when hampered by the presence of electrolytes.
47
.. ... .
Vol.
CLAY SUSPENSIONS
Clay suspensions in the deflocculated state when filtered through paper will show decided turbidity in the filtrate. Again, such a suspension, after the coarser portion has been allowed to settle out, will give rise to the familiar phenomenon of the Tyndall cone upon passing light through it. Clay suspensions are affected in a very pronounced manner by various reagents, both electrolytes and non-electrolytes. Probably the first striking phenomenon observed in this respect is that of absorption. Upon adding solutions of salts like “&I, BaC12, A12(SOd)s, and CuSOa, an appreciable amount of the basic ion is absorbed but practically none of the acid ion. Thus Sullivan6 found that I g. kaolin absorbed between 0 . 0 0 3 8 and 0.0169 g . of CuO from 50 cc. of a solution containing 2 g. of CuS04, but was itself slightly dissolved. Cushmane found the absorption of NH4 from NHdCl to be 0.077, of Ba from BaCl2 to be 0.373, and of A1 from A12(504)3 to be 0.075 per cent after standing three days and using 0.1N solutions. Deeply colored solutions of metallic salts may thus be decolorized by passage through clay. Organic salt solutions like malachite green or methylene blue, consisting of large, complex molecules are absorbed to a very striking extent, and in fact Ashley’ employed the magnitude of absorption of the former as a measure of the colloid content or the plasticity of clay, using a solution containing 3 g. of the dye per liter. This type of absorption follows the general exponential equation with fair agreement. 1
Comfit. rend., 79 (1874), 376, 473.
* Z . anorg. Chem., 8 1 (1902),
158; 41 (1904), 325. a Trans. Am. Ceram. SOC.,6 , 6 5 ; Bureau of Chemistry, Bullet$ns 88 (1904) and 92 (1905). 4 Private communication. 6 U. S. Geological Survey, Bulletin 812. 6 Bureau of Chemistry, Bulletin 92. 7 U . S . Geological Survey, Bulletrn 888; Bureau of Standards, Techno logic Paper 98.
*
