THE HISTORICAL BACKGROUND OF COLLOID ERNST A. HAUSER Massachusetts Institute of Technology and Worcester Polytechnic Institute, Cambridge, Massachusetts
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SEEMS only fitting to me.that I begin by quoting the man whose bicentenary of birth was celebrated only a few months ago. In his book, "Mineralogy and Geology," Johann Wolfgang von Goethe (1749-1832) wrote: "The History of Science Is Science Itself." Another great man, whose centenary of birth also occurred this year, was the Canadian physician, Sir William Osler (1849-1919). In an address delivered before the Royal Society of Medicine, Historical Section, on May 15,1918, he made the following statement: "In science the credit goes to the man who convinces the world, not to the man to whom the idea first occurs." It is to the memory of these two great men that I intend to dedicate the following, as proof of how correct their statements still are today. A survey of the latest textbooks on colloid chemistry reveals only too clearly how little interest most authors have taken in the history of that branch of science dealing with matter which Thomas Graham termed "colloids" (4, 6). It is therefore understandable why most generally all the credit for the discovery of the colloidal state of matter goes to him. I certainly have no intention of belittling his outstand'mg contributions to science. He undoubtedly deserves full credit for having been the first to convince the world that matter can exist in a state intermediate between a true solution and a coarse solid condition. We also owe to him most of the terminology still used today in colloid chemistry. If one surveys the literature prior to Graham's eontributions objectively, however, it must be admitted that many substances and phenomena now specifically classified as colloidal were known to chemists much earlier. One book (6) has been devoted to the So history of colloids. Of the nine Papers reprinted therein, however, only four antedate Graham's first publication. If these four papers actually constitute all that antedate his work, then ~~~h~ should be to all the credit he has been receiving. This is not the case, however, as a critical review of pre-Graham literat~re reveals. A better knowledge of the history of science is needed to develop better scientists. As the philosopher C. E. M. joad quite recently pointed out, our education seeks primarily to enable a man to acquire a living, rather than to acquire a life worth living. He suggested that every student in science should take a 1 Presented before the Division of History of Chemistry at the 116th meeting of the American Chemical Society at Atlantic City, New Jersey, September, 1949.
course in the history and problems of philosophy, supplemented by the history of scientific ideas. How true this is in the field of colloid chemistry should be evident from the following historical excursion. The oldest printed reference to what we term today a gold sol, which I have found so far, dates back to the year 1618 (1). This book gives no information in regard to how "drinkable gold" was produced in those days, but discusses in great detail its application as a cnrative for many illnesses. Although the author does not offer any specific opinion for its effectiveness, he does postulate that the gold most probably coats the diseasecausing germs and thereby prevents them from being harmful. Probably the first book printed in German dealing with what we now know as colloids was published in 1676 (8). It discusses the production of "drinkable gold and silver" as practiced by some chemists at that time. The author disagrees quite emphatically with the claims made by others about the healing powers of drinkable gold. Not having been able to make such preparations himself, he drew the conclusion that all statements pertaining to the production and use of aurum potabile are unfounded and only made to enrich a few scoundrels. In contrast thereto another German published a book in 1684 (9) in which thirty experiments are offered to teach the production of what later became known as gold-ruby glass. To prove that this author has antedated Graham and the colloid chemists who followed him not only in the preparation of gold-ruby glass but also in the preparation of a gold sol, I would like to quote in translation one of his exueriments. Dissolve finely beaten gold flakes in aqua reg*, this is apuajort in which salmiac (ammonium chloride) had been diiisolved. One obtains upon desiccation a yellow residue which is water soluble. In acidic condition it is termed solution awi. Take a large glass full of pure well water and add dropwise a few drops of the solution aun'. Then place a piece of cleanly scraped English tin into the glass. If it is left therein for some time it will look quite black, but after a few hours it begins to color the water red and finally the water reaches maximum hrilliancy. The tin is then removed. I take this gold sol precipitated by the tin and mixit thoroughly with six parts of Venetian glass talc, grind carefully, mix with my silica, and upon melting obtain the most beautiful ruby glass flux, ,
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Still another German book devoted to the medical application of "drinkable gold" (7) is of interest from a colloid point view for the passages: "The gold could be dissolved readily by first
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mixing it with salt and melting them together. A yellow solution is obtained when dissolving it in water. By adding alcohol and heating a cherry-red color apDears. What amazed me mas that the solution if held against the light showed opalescence like a rainbow. The gold is seemingly not completely dissolved but still present in comminuted form." Next I would like to quote from a book written by a woman in 1794 (3). Thinking that phosphorus applied in the form of vepour through the medium of water might he more effectual than a solution of it in ether, I immersed a small bit of silk in an aqueous solution of gold, and suffered it to dry a.little; it was then suspended in a phial over a little water, into which a s m l l bit of phosphorus was previously introduced: the phial was then corked, and placed on hot sand: the phosphorus began to melt, and ascend in white vapours, which, as soon as they reached the lower end of the silk, gave it a brown tinge, succeeded by a purple; and the gold began to assume its metdlic splendour: in a short time these appearances were evident over the whole silk. The following propositions are deducible from these experiments. 1. Water does not promote the reduction of gold merely by dissolving, and minutely dividing, the particles of the salt, and thus diminishing their attraction of cohesion, and consequently increasing their chymical attraction, as I f i s t supposed; for were this the case, ether and alcohol, which equally dissolve, and divide the salt, should produce the same effect. 2. Ether and alcohol do not promote these reductions without the aid of water; for it is evident from the experiments related, that the few particles of reduced gold, which appear, when they are employed, depend entirely on the quantity of water, which they leave in the silk during their evaporation, and that attracted from the air by the solution of gold, and hy the phosphorus during its combustion, both of which have a strong attraction for water. 3. Phosphorus does not reduce gold by giving the metallic earth phlogiston, as the Phlogistians suppose; for were this opinion true, B solution of gold in ether, or alcohol, should be reduced by the phosphorus as effectually as a solution of gold in water is. 4. Phosphorus does not reduce gold, by combining with, and separating, the oxygen of the gold, as the Antiphlogistians assert; for were this the case, the particles of the phosphorus so attenuated by the ether, should reduce a solution of gold in ether, or alcohol, as well as solution of gold in water, since the impediment opposed by the attrltction of cohesion is equally removed in both cases.
And now in conclusion let me quote a few passages from Michael Faraday's Bakerian lecture (2) which deserves far more attention than they have so far received, a t least from an historical point of view. I am referring specifically to the chapter on "Diffused particles of gold-production-proportionate sizecolour-aggregation and other changes." After explaining the procedures he used in making the goldcontaining fluids and how they appear when a concentrated beam of light is passed through them, he adds the following: The particles in these fluids are remarkable for a set of physical alteratiotionsoccasioned by bodies in small quantities, which do not z t chemically on the gold, or change its intrinsic nature; for through all of them it seems to remain gold in a fine state of division. They occur most readily where the particles are finest, i. e., in the ruby fluids, and so readily that it is difficult to avoid them; they are often occasioned by the contact of vessels which
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are supposed to be perfectly clean. An idea of their nature may be obtained in the following manner. Place a layer of ruby fluid in a clean white plate, dip the tip of a glass rod in a solution of common salt and touch the ruby fluid; in a. few moments the fluid will become hlue or violet-blue, and sometimes almost colourless; by mingling up the neighbouring parts of the fluid, it will be seen how 1mge.a portion of it can be affected by 8. small quantity of the salt. By leaving the whole quiet, it will be found that the changed gold tends to deposit far more readily t h m when in the ruby state. If the experiments he made with a body of fluid in a glass, twelve or twenty-four hours will suffice to separate gold which in the ruhy state has remained suspended for six months. The fluid changed by common salt or otherwise, when mast altered, is of a violet-blue, or deep hlue. .4ny tint, however, between this and the ruhy may be obtained, and, as it appears to me, in either of two ways; for the intermediate fluid may he a mixture of ruby and violet fluids, or, as is often the case, all the gold in the fluid may be in the state producing the intermediate colour; but as the fluid may in all cases he carried on to the final violet-blue state, I will, for brevity sake, describe that only in a particular manner. The violet or hlue fluid, when examined by the sun's rays and a lens, always gives evidence showing that the gold hasnot beenredissolved, but isstillin solid separate particles; and this is c o n h e d by the nonaetion of protochloride of tin, ruhich, in properly prepared fluids, gives no indication of dissolved gold. When a ruby solution is rendered hlue by common salt, the separation of the gold as a precipitate is greatly hastened; thus when a glass jar containing about half a pint of the ruby fluid had a few drops of brine added and stirred into the lower part, the lower half of the fluid became hlue whilst the upper remained ruhy; in that state the cone of sun's rays was heautifully developed in both parts. On standing for four hours the lower part became paler, a dark deposit of gold fell, and then the cone was feebly luminous there, though as bright as ever in the ruby above. In three days no cone was visible in the lower fluid; a. fine cone appeared in the upper. Such results would seem to show that this blue gold is aggregated gold, i. e., gold in larger particles than before, since they precipitate through the fluid in a. time which is as nothing to that required by the particles of the ruby fluid from which they are obtained. Many other bodies besides salt have like action on the particles of gold. A ruby fluid is changed to or towards blue by solutions of chlorides of calcium, strontium, manganese; sulphates of magnesia, manganese, lime; nitrates of potasss, soda, baryta, maenesis. maneanese: acetates of ~otassa.soda. and lime: these
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feebly.. Again, though these particles are so finely divided that they pass easily through ordinary filters, still a close filter catches some; and if a ruby fluid he passed through again and again, the paper at last becomes of a rosy hue, because of the gold which adheres to it; being then well washed, and, if needful, dried, the gold is again ready for experiment.
All these citations, and particularly Faraday's, offer ample evidence that it had been realized by carefully observing scientists long before Thomas Graham that matter can also be present in a state intermediate between ionic dimensions and those discernible in a microscope. What I consider even more important is the fact that it also had been realized prior to Graham that matter present in this range in a t least one dimension exhibits properties which are not dependent upon its chemical composition. REFERENCES (1) ANTONII,F.:
"Panacea Aurea," Bibliopolio Frobeniano,
JOURNAL OF CHEMICAL EDUCATION
266 London, 1618. M.: Phil. Trans. Roy. Sac., 147, 165, 166, 173 (2) FARADAY, (1857). (3) FULHAME, MRS.: "An E s ~ a yon Combustion,'' J. Cooper, London, 1794. (4) GORTNER, R. A,: J. CBEM.EDUC.,11, 279 (1934). (5) GRAHAM, T m . : Phil. T~ans.Roy. Sac., 151, 183 (1861). (6) HATSC~EK, E.: "The Foundations of Colloid Chemistry,"
Ernest Benn, Ltd., London, 1925. (7) HELCHER, H. H.: L ' G ~ l Tinctur," d J. H. Klossen, Bresslau and Leipzig, 1718. (8) KUNKELS, J.: Ammerkungen van den Fixen und Euechtigen
Salsen-Auro und Argento potabile," G. Sohultzens, Hamburg, 1676. (9) ORSCHALL, J. C.: "Sol sine Veste," J. Koppmayr, Augbpurg, 1684.
