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obvious that greater economy is obtainable when a glue kettle containing 500 lbs. of mixed glue is prepared with 100 lbs. of starch than when 200 lbs. are required. I n fact, the spread obtainable with the glues of the older type containing 2 or 2‘/2 parts of water averages between 45 and 55 sq. f t . of glue line per lb. of dry glue. With the 4 : 1 glues t o which certain colloidal materials have been added this spread is easily doubled. Thus, it becomes apparent that the amount of water to be dried from a panel glued with a 4 : 1 glue varies but little with that to be dried from one glued with a 2 or 2l/4 : 1 glue, since with the former the same amount of starch spreads twice as many panels.
EXTENT OF INDUSTRY The extent of the vegetable glue industry is apparent when it is appreciated that there is an annual market in this field for 20 or 30 million lbs. of starch in this country alone. There are about 1000 concerns using vegetable glues in the manufacture of standard panels, box-shooks, and furniture.
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There are perhaps a dozen concerns producing these various vegetable glues. The price to the consumer of these vegetable glues is between 6 and 9 cents per lb. A fair price for animal glues for the same purpose to-day is between 13 and 20 cents, and in the past has been even higher. Thus, there is a saving of a t least one-half the glue bill when ordinary 2 : 1 vegetable glue is substituted for animal glue and this figure can be reduced further by employing the 4 : 1 glues recently developed. It should be pointed out there are many varieties and grades of starch, and that not all of them are of equal value in producing a vegetable glue. Moreover, there is a wide variation in most of these grades of raw starch, which makes it a precarious venture for a plywood manufacturer to buy raw starch on the open market and turn this material into a veneer glue. Unless he has a chemist familiar with starches and vegetable glues and capable of maintaining a uniform product, the few cents per pound saved on materials cost will be far overbalanced by the losses from poorly glued stock.
Colloid Chemistry By Jerome Alexander E X - C H A I R M A N , COXMITTEE ON COLLOIDS, NATIONAL
HE GROWING realization of the importance of colloid
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chemistry and its practical applications is evidenced by the fact that whereas the Decennial Index of Chemical Abstracts (1907-1916) contains a little over 12 columns of titles indexed directly under colloids, the 1921 index alone contains over 3 columns. I n both cases no note has been taken of a large number of titles of papers dealing with colloid-chemical questions, but indexed under a wide variety of other head?. The Kolloid Zeitschrijt, which appeared initially in 1906, is now in its 30th volume, and 14 volumes of monographs have been issued in Kolloidchernische Beihejte. Since its organization the National Research Council has had its Committee on Colloids, and the British Association for the Advancement of Science has considered the subject of such importance, that since 1917 it has issued three “Reports on Colloid Chemistry and I t s General and Industrial dpplications.” Each report contains a series of separate papers; a fourth report is in preSs, and a fifth is in preparation. A few years ago the Chemical Society of London and the Faraday Society held a special joint symposium on colloid chemistry mhigh mas attended by quite a number of prominent continental chemists, and though the papers read were published in several journale, they were deemed of such importance that they were printed separately, together with some older inaccessible work. Many universities and colleges here and abroad are giving separate courses in colloid chemistry, and no course in theoretical or technical chemistry is complete without giving it due consideration. Analysts, biologists, and physicians must take note of it. I n almost every branch of chemistry and technology, workers of unquestioned reputation and ability are producing striking results. Why is it, then, that there are still some who shrink from recognizing colloid chemistry as a distinct zone in the wide field of chemical and physical science, and cling to the idea that colloid chemical facts must
RESEARCH COUNCIL, N E W
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be explained upon the basis of “simple chemical principles?” Just criticism has been leveled a t some who fail to giv due weight to purely chemical considerations, or who think that a problem may be disniissed with the mere statement that it is “colloidal.” But the main cause I the tendency referred to is an attempt t o stretch the original and long-established meaning of the term ‘LchemicaI” to cover all cases where attractive forces result in combination. Thus S. H. C. Briggsl goes SO far RS to consider as “chemical” the forces which hold atomic kernels and electrons together to form elements. If, with Langmuir, we call all residual electronic forces “chemical,” then adsorption compounds are chemical c o m p o u n d s . Atoms or Champlain S l u d i o s , N. Y . molecules without R JEROXE ALEXANDBR residual field of force would form a perfect gas, but even helium does not meet this criterion. Elemental atoms and all molecuies a r e ’ anisotropic or polar, and after the satisfaction of what have been heretofore regarded as the normal chemical valences, there remain powerful residual or stray fields of electronic force which are responsible for what we ordinarily term the physical properties of the substance--its hardness, melting point, boiling point, solubility, viscosity, etc. >’a
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Much difficulty would be avoided if we adopt the classification suggested by P. E. Wells: 1-Electronic forces-those which bind electrons together into atoms. 2-Atomic f6rces-those which bind atoms together into molecules. 3-Molecular forces-those which bind molecules together into masses. &Molar forces-those which affect masses, i. e., gravitation. There is no sharp demarcation between 2 and 3, and the forces involved in colloid phenomena bridge the gap.2 So after the novice is taught t o distinguish between physical mixtures and chemical compounds, he must gradually learn t h a t no sharp distinction exists. Without in any way attempting t o give a complete or even a critical selection from the wide field, there are here briefly mentioned a few colloid subjects of theoretical interest, followed by a number of instances where recent developments in colloid chemistry have been applied t o technical problems:
THEORETICAL seems probable that changes in sensitive bio-colloids constitute one important mechanism whereby evolution proceeds. 2-It has been shown that adsorbed ions are necessary to the formation of stable colloidal solutions and jellies. 3-Nephelometers have been developed and applied to many quantitative determinations. &With the MacMichael viscosimeter the viscosity of colloids may now be expressed in absolute or c. g. s. units. &The size of colloidal particles has been checked with the aid of an oscillating electric field. 6-Much work has been done on fogs, smokes, and adsorbents. 7-Much work has been done on catalysis, its acceleration and inhibition. 8-M . H. Fischer and Wo. Ostwald, among others, have shown the importance of the state of swelling, or solvation in colloids. 9-After showing the importance of H-ion concentration in protein solutions, J. Loeb applied the Donnan theory of membrane equilibria as developed by Procter and Wilson, and worked out a mathematical and quantitative theory of the colloidal behavior of proteins. 10-McBain has developed the idea of colloidal electrolytes, i. e., salts in which one of the ions is replaced by a heavily charged hydrated ionic micelle (a colloidal particle of great conductivity). 11-&I any biological reactions have been explained on the basis of colloid chemistry,-i. e., clotting of blood, coagulation of milk, Wassermann reaction, anaphylaxis, etc. 12-Ultrafiltration and ultracentrifugation have been developed. 13-Ultramicroscopy has made rapid strides. 14-Swelling and shrinking of colloids have received wide attention from an experimental and from a theoretical standpoint. 15-The making and breaking of emulsions as well as their reversal of phase have been much studied. 16-Many applications of colloid chemistry to chemical analysis have been noted. TECHNICAL APPLICATIONS 1. FZOTATION-over 60,000,000 tons of ore are treated annually. Adsorption, surface tension, and flocculation are important factors here, and because of the great commercial interests involved, much work has been done on the theoretical and practical sides of flotation problems. 2. COLLOIDAL ADSORBENTS (silica-gel, specially prepared carbons, fuller’s earth)-The importance of proper carbon for gas masks was proved during the war. Patrick’s silica-gel is largely used to recover casinghead gasoline, and petroleum distillates are purified by various adsorbents. Zerban reports that impurities in cane-sugar juice are largely colloidal and mainly removable by adsorption,+. e., with 0.5 per cent Filtercel and 1 per cent Norit. 3. COLLOIDMILLS-These are essentially high-speed disintegrators arranged for wet grinding. A protective colloid is usually added to the water or other fluid used, to prevent re-aggregation of colloidal particles originally formed. The mill is said to find application in the following industries : soap, viscose, cellulose, 1-IC
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4 In fact many, among them Faraday, have expressed the view that there is only one ultimate kind of force.
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oil, rubber, sugar, and glue. Products of special properties are without doubt produced, but until definite information is had as to output, cost of power and repairs, judgment as to the commercial status of the mill must be suspended. 4. ULTRACENTRIFUGES (and ultrafilters) have been applied to the clarification of many fluids,-i. e., varnishes, wool-scouring liquors (with recovery of. wool grease), gelatin. 5. WATER-PURIFICATION AND SEWAGE DIsPosAL-The Journal of the American Water Works Association shows many extensions in this field. New sand filters do not function properly until a bacterial gel or slime forms on their surfaces. The same applies to sewage filters. 6. TANNING-Much valuable work has been done by H. R. Procter and J. A. Wilson, who have applied Donnan’s theory of membrane equilibria, which for some time lay buried in the Zeitschrijt j d r Elektrochem. 7 . LUBRICATION-W. B. Hardy showed that powerful adsorption a t the interfaces involved is an essential in lubrication. Southcombe and Wells patented the addition of a small amount of free fatty acid (about 1 per cent) to petroleum oils. This lowers the interfacial tension between oil and metal. The surface tension between oil and graphite is less than between oil and metal; hence graphitizing aids lubrication. 8. COLLOIDAL FuEL-This consists of finely powdered coal, tar, etc., dispersed in fuel oil with the aid of a protector (usually a lime soap). Most of the dispersed material is far above colloidal dimensions, so the fuel has a “life” limit that may extend to months, after which it may be “revivified” by agitation. It should economize fuel oil and use up culm and other wastes. 9. METALLURGY-Properties of metals and alloys are dependent upon fineness of grain, and this may be partially within the colloidal zone. Scherer showed that even amicroscopic particles of colloidal gold consist of crystals, but that with colloidal silica and stannic acid crystalline and haphazard or amorphous groups of molecules may coexist. 10. PETROLEUM-The viscosity of oils depends upon their previous history, probably because of variations in the degree of dispersion of waxy bodies present. The breaking of emulsions in refining and their formation in lubrication are colloidal problems. 11. CLAu-The use of deflocculators in purifying and casting clays has been largely developed. 12. AGRICULTURE-colloid problems in soils and fertilizers are being widely investigated. A small amount of “ultra-clay’’ produces a powerful effect on a soil. 13. INSECTICIDES,~. e., lead arsenate, are more efficient and stick better when in colloidal state. Minute quantities are sufficient to kill insects, and it is wasteful to supply more than the necessary dose. 14. “FIREFOAM,”used in blanketing fires, is a carbon dioxide froth made by mixing solutions of alum and sodium bicarbonate. A protective colloid, such as glue, dextrin, or saponin, is used to stabilize the finely dispersed foam. 15. RUBBER-The importance of the state of subdivision of “fillers” is recognized. Much work has been done on vulcanization, and on the coagulation of latex. Glue is now worked into rubber tires on a large scale, and is said to improve their life. 16. BAKINGAND BREAD-MAKING-The Swelling and Viscosity of glutens are being investigated, also the prevention of “staling” by milk, fat, etc. The effect of traces of salts on flour is important. 17. VARNISHES, PAINTS AND PIGMENTS-work has been done on thickened oils (linseed and china wood oil), resins and synthetic resins (bakelite), and varnishes. The degree of subdivision of pigments in paints, and their maintefiance in dispersion and suspension are important factors in paints. 18. MILK AND MILK PRODUCTS-Ice cream is improved, stabilized, and made more digestible by protective colloids (gelatin, eggs, etc.). Homogenized milk and cream having increased viscosity are largely used, and artificial milks are made. Protective colloids are used in preparing margarines. Little work has been published in regard to cheese. Besides translations and new editions, increasing numbers of books are appearing originally in English. Laboratory manuals have been issued by E. Hatschek and by H. N. Holmes. I n 1921 W. D. Bancroft published in THISJOURNAL a list of 200 research problems in colloids, which list was issued separately by the National Research Council. I n looking up indexes for references, it must be borne in mind that many papers and books of interest to the colloid chemist are not indexed under “colloid.” Such headings a s
