BAUDRIMONT AS COLLOID CHEMIST
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BY WILDER D. BANCROFT
Last spring Mr. W. A. Bender, chief chemist of the Douglas Pectin Corporation, told me that in the Trait4 de Chimie, published in 1844-1846, Baudrimont had included a great deal of very good colloid chemistry. After some difficulty I succeeded in securing a copy of the book and I find that Mr. Bender had not exaggerated things in the least. I n the second volume, pp. 842-850, Baudrimont has a chapter on the general characteristics of particulate or non-crystallizable substances. Since particulate is not a word in common usage, I am going to substitute for it the word granular, which means the same thing. “Organic substances occur in a sekies of stages, rising from the level of inorganic compounds to the structure of organized bodies. In the lowest stage they are like inorganic compounds. Like them they occur and react in definite proportions; they are solid, liquid, or gaseous; their molecules have fixed axes which give them a structure and a definite crystalline form; but they are characterized by their origin and by the nature of the elements which constitute them, typical instances being sugar, alcohol, and the gaseous carbides [hydrocarbons], etc. I n the next stage the substances do not .have compositions described by the law of definite proportions, they combine in varying proportions, they are formed of particles visible under the microscope and having no definite axes. When left to themselves the particles either remain free and take the form of a liquid, like albumin, or they agglomerate and form tuberculous masses like the gums and the resins. At a still higher stage the particles arrange themselves under the influence of definite forces, forming organic tissues, like the cellular tissues, the muscles, and the nerves, Finally they assume forms and methods of arrangement which vary with the beings to which they give rise. “The first stage is that which is represented by organic compounds in the strict sense of the word, by the substances described in the first part of the organic chemistry under molecular or definite compounds. The second stage is represented by substances, whose constituent parts, though still subject to the laws of mechanics, adopt nevertheless the form of the constituents of the organic tissues. They are represented by spheroidal particles which are either liquid or seem to be; particles which are formed under the influence of forces peculiar to or inherent in them, if we may use such a phrase. These substances I have called granular and they will be described in the second part of the organic chemistry. At the next higher stage, if exterior forces supervene, the granular constituents agglomerate according to certain laws and form organized beings as has been said. These last two groups of substances belong necessarily under general anatomy and physiology and need not be discussed in a treatise on chemistry, although they have really been studied by chemists. There are now text-books on anatomy and physiology which include all the chemical ideas which are needed.
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“The granular substances are fornied of spherical or spheroidal particles having diameters varying from two hundredths of a millimeter to about one millimeter. This enormous variation in volume can be observed in some cases with a single kind of particle, starch, for instance. When the particles are brought in contact with certain liquids, they either take up the liquids and swell considerably or they yield a part of the liquid they contain to the surrounding fluid and shrink. The first phenomenon occurs strikingly with starch grains in boiling water or in hot acidulated water; with histose, the cellular tissue of animals, in presence of boiling water. The second phenomenon can be observed by putting grains, such as gum arabic, into alcohol after they have swelled in water. “When the particles are swollen very much and are held in suspension in a liquid, they seem to be dissolved but they are not. Albumin and gum arabic are usually called soluble in water; but they are not really soluble and only seem to be, their special structure permitting the particles to slide one upon another and thus duplicate in mass the properties of a liquid, while they also give this seeming liquid n special viscosity because of the mutual adhesion. “If the liquid in contact with the grains has some chemical substance in solution, this substance may penetrate the grains and be held there by B variable force, of a nature similar to that which causes solution and capillary phenomena. Very soluble salts may therefore be retained by the particles even after a number of washings. It is for this reason that it is almost impossible to remove potassium acetate which has been adsorbed by protein. The granular substance may even protect the adsorbed substance so completely that the latter will resist a chemical attack which would ordinarily dissolve it. Fibrin will retain phosphates so that only with extreme difficulty can hydric salts [acids] dissolve them readily under ordinary conditions. There seems to be a sort of adhesion which holds together the particles and the substance fixed by them. “The substances held in a state of pseudo-combination by the granules modify the properties of these latter remarkably. Since the granular substances are generally not soluble and would lose all their characteristics properties if they were soluble, the adsorption may prevent them from expanding [dispersing] sufficiently in a liquid to appear soluble and we therefore say that they have become insoluble. Substances, which make the granules contract, may precipitate them. “Among the modifications of the granules when in pseudo-combination, two are very remarkable. In one the particles become visible and may be said to be solidified; but they remain isolated. This occurs with bariiim hydroxide and albumin. In the other case the particles contract and agglomerate to form a clot. In other words, coagulation occurs. We get this when alcohol, chloromercuric acid, or the mineral acids, with the exception of phosphoric acid, react with albumin. To what is due the repulsion or adhesion? What gives rise to these differences? These are questions with which
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the future will have to occupy itself and which will perhaps clear up what happens in the organs of living beings when the constituents which form them are fixed. “The union just described is very different from chemical combination; it does not affect the molecules and is not according to definite proportions. The amounts which combine are proportional to the time [?I and to the temperature. This accounts readily for the fact that chemists have believed in an increasing saturation capacity which nevertheless gave definite compounds. Instances of this are the facts observed by M. FrCmy in his work on pectin and by M. Mulder in his work on fibrin. The latter chemist claims that fibrin obtained from blood from the jugular vein of a cow gave a sesquifibrate of silver, while fibrin prepared from arterial blood obtained by cutting the carotid artery of the same animal gave quadrifibrates. All the alleged, definite compounds of albumin, fibrin, pectin, pectic acid, etc., are indefinite compounds in varying proportions, which may nevertheless have a definite limit; but this limit is comparable to the limiting amount of water which a sponge can take up. “There is one conclusive proof of the views which have just been put forward. So long as a granular substance is not destroyed, it keeps its particulate state no matter what combination is formed. I have treated pectin with a number of reagents, obtaining apparent compounds and double decompositions. In every case the new compounds were particulate and when one regenerated the pectin from a series of compounds, it had its original properties and its granular form.” “The extraction and purification of granular substances is a very special problem. They cannot be dissolved and allowed to crystallize; they cannot be distilled or sublimed. If one were to dissolve them, to make them form real compounds or to change their physical state, they would lose entirely the structure which characterizes them and they would not regain it, if we assume that this structure us usually the result of organic functions. We must therefore purify granular substances by a series of treatments which will not alter them but which will destroy the impurities which are present. We obtain cellulose, protein, and casein for instance, by treating them successively with acids, alkalies, ether, alcohol. “The occurrence of inorganic compounds in the granular substances interferesverymuchwith the accuracy of the analytical results that one gets. We usually assume that the weight of the organic portion is equal to the difference between the total weight of the substance and the weight of the ash obtained by combustion. The ashes, however, are not necessarily in the same state of combination as in the original substance. The iron may be ferric and not be ferrous; there may be carbonates instead of salts of organic acids. If such analyses are to be significant, it is essential to know the form in which the inorganic bases occur in the organic substance, t o make an accurate analysis of the ash, to calculate the form in which the bases were, and to correct the experimental data ir, accordance with this.
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“As has already been said the granular masses behave like liquids, jellies, or amorphous and vitreous substances. Liquids containing particles in a state of pseudo-solution [colloidal solution] are always viscous. If the viscosity increases, that is if the granules become more adherent, they unite and form a jelly, like starch, paste, the mucilaginous gums, pectin, gelatin, and chondrin. I n the solid state they form lumpy masses like the gums, the starches, the fats, and cellular tissue. The property of forming a viscous liquid or of setting to a jelly is so limited to the granular substances that I have not found a single substance with this property which did not have a particular structure. Typical cases are the glairy substance in mineral waters, the mucus of viscous fermentation, the pseudo-solutions of gums, albumin, animal jellies, etc. All these owe their properties to the granular nature of their constituents. I even dare to add that all substances, like the gums, which are amorphous and vitreous are particulate and that so are potassium silicate jelly, viscous sulphur, the different forms of glass, the hydrated silica obtained by M. Ebelmen, hyalite, the resins, agate, etc. “The particles are formed by the dispersion of a pre-existent liquid or by the formation of one liquid in another liquid which cannot dissolve it. A small amount of liquid left to itself in the mass of another liquid will tend to become spherical and will become spheroidal under the influence of gravity or other forces. Onesees thisif one drops mercury on a table or disperses oil in mucilage. One must therefore assume that all the organic granules have passed through the liquid stage. . . “The knowledge of the granular state of organized bodies clears up many facts hitherto inexplicable and leads to many applications. It explains the formation of organic substances, a number of physiological phenomena, the part played by mineral fertilizers, the constitution of the skeleton, the dyeing of textiles, the tanning of skins, etc. “The opinion has already been expressed that organic tissues were formed of granules’ and this view was rejected for many reasons, among others that some of the infusoria have organs smaller than the smallest granules and that consequently all animal tissues cannot’ be particulate. That may be true but they have credited the infusoria with many organs which they do not possess and I am also prepared to state that many of the infusoria are formed entirely of globules. Anyhow, this does not invalidate anything which has been said because we have been talking about beings higher in the organic scale, for which the proof is positive and not to be overthrown by any objections. ‘(We may therefore consider all the statements in the preceding paragraphs as absolutely accurate. They are true for all the substances which are to be discussed in the remaining pages of this volume. It is in consequence of unpublished microscopic observations and tests, covering a period of nearly twenty years, that I am able to gather together and to correlate all these results, which create a new branch of chemistry.”
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Here Baudrimont is apparently using the word in the sense of cells.
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Baudrimont considers that the particles of gelatine, for instance, swelI in water and thereby become invisible. He does not seem to have considered the possibility of their being dispersed into smaller particles and consequently we cannot credit him with a knowledge of peptization. Baudrimont did not know that the soaps form true solutions in alcohol and colloidal ones in water and he believed in colloidal substances rather than colloidal states; but so did Graham and, for that matter, so did the rest of us up to relatively few years ago. On the other hand Baudrimont was perfectly clear that the second substance in a colloidal solution is not in solution but only appears to be. He knew about adsorption and, though he never heard of an adsorption isotherm, he knew that adsorption may soon reach a practical limit with increasing concentration. He knew that suspended particles may swell without forming definite hydrates and he knew that jellies are formed by the partial agglutination of the suspended particles. He knew that adsorption may change the apparent physical and chemical properties of the adsorbed substance and that the adsorbed substance may coagulate and precipitate the adsorbing colloid. He knew that most of the alleged compounds with colloids did not exist. In short, Baudrimont knew a great deal more about colloid chemistry ninety years ago than some distinguished scientific men do now. One or two special quotations will emphasize Baudrimont’s point of view. ‘‘Gum arabic appears to be soluble in water but does not dissolve in it. The particles separate, imbibe liquid, become soft and flexible, and therefore share the dynamic conditions of equilibrium of the water which holds them in suspension. The viscosity of the liquid is increased considerably by the adhesion of the particles of gum arabic. Alcohol cannot break apart the particles of gum arabic and hold them in suspension as water does. When one adds alcohol to the seeming solution of gum arabic, it causes them to contract and precipitate,” p. 853. “Casein occurs in milk and appears so completelydissolved that it is impossible to see it. The only particles that one sees directly are those of the butter fat. Nevertheless suitable reagents cause the casein to contract and the particles then become visible. For a long time casein was considered to be soluble in water; but, quite independently of my observations. M. Rochleder has shown that water does not dissolve any casein when the latter is pure,” p. 879. Casein is not considered by Baudrimont to form definite compounds either with acids, alkalies, or salts. “Albumin occurs in the form of absolutely invisible particles when one examines it without any additions; but when a suitable reagent is added the particles become readily visible and easily recognized. Barium hydroxide solution is the best reagent for this purpose. When made visible in this way, the particles of blood albumin are much smaller than the red blood corpuscles and are only 0.005 mm in diameter. The particles of egg albumin from two lots of hen’s eggs were 0.006 mm in diameter,” p. 884. “Gelatine is particulate, solid, transparent, colorless, denser than water, hard like horn, fragile, and with a conchoidal fracture when it is very dry, while it is flexible, very elastic, and very tough when it is a bit damp. . . Put in contact with water
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at room temperature, it swells, losing its limpidity and solidity. If, after it is permeated by water [not hydrated], it is heated to 50’ or 60°, the gelatine appears to dissolve completely; but it is really only held in suspension, as can be shown by microscopical examination after treatment with suitable reagents, and as is also proved by the gelatinous state to which it returns on cooling,” p. 896.
I n the first volume Baudrimont points out, p. 198, that probably all solids show what we now call selective adsorption, especially when they are porous with fine pores. He considers, p. 81, that dyes are taken out of solution by the textile fibers and made apparently insoluble without forming any definite compounds. The phenomenon is analogous t o the decolorizing by charcoal, which everybody knows does not involve the formation of definite chemical compounds. Even the taking up of cochineal by cotton mordanted with alumina is thought to be a case of adsorption, p. 198. Although very clear on the subject of dyeing, the question of mordants was rather too much for Baudrimont.‘ “Alum alone does not cause any precipitate in a solution of carmine; but it has the remarkable property of fixing the carmine on textiles. A textile can be immersed in a solution of carmine without being dyed in the least. It only soaks up the dye which can be removed completely by a few washings. Alum does not precipitate carmine and yet, if the textile has previously been impregnated with an alum solution, the coloring matter becomes fixed on the cloth and cannot be removed ay any number of washings. This is a general phenomenon. Infusions or solutions of coloring matters can only be fixed upon textile by metallic salts. Such salts are called mordants.” What, Baudrimont has overlooked is that impregnating cloth with a solution of alum precipitates in the fibers either alumina or a basic salt. Either of these will take carmine out of solution in the absence of the cloth. One must not hold this minor slip up against him in view of what he goes on to say about dyeing. ‘TJnder the conditions just mentioned, the cloth, or the threads from which it is made, function by some sort of capillary action, for they are not destroyed. The dye is only fixed on their particles forming a special type of compounds in which the molecules are not changed. Such compounds have been called particulate [inddinite or adsorption compounds]. For any coloring matter, inorganic or organic, to unite with a textile and dye it in a durable manner, the dye must be dissolved in a medium so that it can impregnate the textile and be made insoluble by it. This is the fundamental principle in all dyeing. A few instances will suffice. Orpiment [arsenious sulphide] is used as a dye by dissolving it in ammonia, dipping the cloth in the bath, and letting the ammonia evaporate, when the cloth will be found to be dyed. One can produce double decomposition in the fabric, as in dyeing yellow, by impregnating the cloth in a solution of a lead salt and then dipping it in a solution of potassium chromate which reacts with the lead salt to form lead chromate. Dyeing with Prussian blue i s done in a similar way. Indigo white, dissolved Trait6 de Chimie, 2, 24, 756 (1846).
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in water, will penetrate the threads and becomes insoluble and blue on contact with the oxygen of the air. As has been mentioned, dyes may be fixed on the fabric by mordants. The sole function of mordants is not to fix dyes. Different mordants may give different colors and a single immersion in a madder bath may dye the cloth five or six different colors according to the mordants printed on the cloth in advance.” Baudrimont’ might have discovered the mass law years before Guldberg and Waags if he had done a few experiments instead of merely talking about them. He calls attention to the extraordinary fact that iron oxide can he reduced to metallic iron by hydrogen with the formation of water and that iron can be oxidized to an oxide by steam with the formation of hydrogen. He points out that these apparently contradictory results are due to the effect of mass. “It is the preponderance of the water vapor over the hydrogen in the one case which causes the iron to be oxidized and keeps the oxide from being reduced. It is the preponderance of hydrogcn over water vapor in the other case which causes the oxide of iron to be reduced and keeps the metal thus produced from being oxidized. Perhaps it would be possible to make a mixture of hydrogen and water vapor which would be without action either on iron or iron oxide. If so, the ratio of the two quantities of these substances would give that of their chemical masses. An experiment of this sort would be easy to do with carbon monoxide and carbon djoxide.” The experiments apparently never were made; but I hope that these quotations will show that Baudrimont was not a man to be forgotten profitably even though his work along these lines had absolutely no effect so far as we now know. It is R discouraging point of view; but apparently a good idea a t the wrong time or by the wrong man, which is perhaps the same thing, is apparently as much wasted as though it had never occurred. One can console oneself however by assuming that if it were not for these preliminary and apparently futile efforts, the right time and the right man would never come. Emereon did not love the Irishman but he thought up a use even for him. Cornell University. I
Trait6 de C,himie, 1, 183 (1844).
