THE DECENNIAL PUBLICATIONS OF THE UNIVERSITY OF CHICAGO PHYSICAL CHEMISTRY IN THE SERVICE OF THE SCIENCES VAN T HOFF THE DECENNIAL PUBLICATIONS OF THE UNIVERSITY OF CHICAGO THE DECENNIAL PUBLICATIONS ISSUED IN COMMEMORATION OP THE COMPLETION OP THE FIRST TEN YEARS OP THE UNIVERSITY'S EXISTENCE AUTHORIZED BY THE BOARD OP TRUSTEES ON THE RECOMMENDATION OF THE PRESIDENT AND SENATE EDITED BY A COMMITTEE APPOINTED BY THE SENATE EDWARD CAPPS STARR WILLABD CUTTING ROLLIN D. SALISBURY JAMES ROWLAND ANGELL, WILLIAM I. THOMAS SHAILER MATHEWS CARL DARLING BUCK FREDERIC IVES CARPENTER OSEAR BOLZA JULIUS STIEGLITZ JACQUES LOEB THESE VOLUMES ARE DEDICATED TO THE MEN AND WOMEN OF OUR TIME AND COUNTRY WHO BY WISE AND GENEROUS GIVING HAVE ENCOURAGED THE SEARCH AFTER TRUTH IN ALL DEPARTMENTS OF KNOWLEDGE CROCKER PHYSICAL CHEMISTRY IN THE SERVICE OF THE SCIENCES PHYSICAL CHEMISTRY IN THE SERVICE OF THE SCIENCES BY JACOBUS H. VAN 'T HOFF MEMBER OF THE PRUSSIAN ACADEMY OF SCIENCES, PROFESSOR ORDINARIES HONORARIUS IN THE UNIVERSITY OF BERLIN, SPECIAL LECTURER AT THE DECENNIAL CELEBRATION OF THE UNIVERSITY OF CHICAGO ENGLISH VERSION BY ALEXANDER SMITH OF THE DEPARTMENT OF CHEMISTRY THE DECENNIAL PUBLICATIONS SECOND SERIES VOLUME XVIII CHICAGO THE UNIVERSITY OF CHICAGO PRESS 1903 Copyright 1903 BY THE UNIVERSITY OF CHICAGO HERRN DR. WILLIAM RAINEY HARPER, PBESIDENTEN DER UNIVERSITAT CHICAGO, der mit einem Organisations-Talent, das mich mit Bewunderung erftillt, innerhalb zehn Jahre eine grosse Universitat ins Leben gerufen hat, mochte ich diese englische Ausgabe meines Werkes widmen. Dass unter seiner Ftihrerschaft der Einfluss, welchen sich die junge Anstalt schon zu verschaffen gewusst hat, von Jahr zu Jahr an Ausdehnung und Tiefe gewinnen moge, ist mein aufrichtiger Wunsch. J. H. VAN 'T HOFF. CHARLOTTENBURG, 16ten Juni, 1903. 125517 AUTHOR'S PREFACE THE following lectures, delivered June 20-24, 1901, were given at the invitation of the University of Chicago on the occasion of the decennium of its foundation. The time for preparation being limited, the lectures were given extempore and the version here presented was adapted for publication from the stenographic report. In order that the whole may present as far as possible a memorial of the interesting fest- ival, the changes made have been confined within the nar- rowest possible limits. The introductory lecture, which appears in this volume as the first lecture of the series, was delivered as one of the addresses before a general educa- tional conference, held in the lecture theater of the Kent Chemical Laboratory, to which the guests of the University were invited. CHARLOTTENBURG, January, 1902. PKEFACE TO THE ENGLISH VERSION DURING the festivities in connection with the celebration of the decennium of its foundation, the University of Chi- cago was honored by the presence of a number of the mosl. distinguished scientific men of the world. Among these, Professor van 't Hoff, who received the honorary degree oil LL.D., was one of the most prominent. As this volume is in some degree a memorial of Professor van 't Hoff's visit, no apology need be offered for printing here the words pronounced by the President of the Univer- sity when, at the convocation ceremony of Tuesday, June 18, 1901, the honorary degree was conferred: JACOB HENRY VAN 'T HOFF, Professor of Physical Chemistry in the University of Berlin; investigator who has brought to bear upon chemical problems a keen and logical mind; endowed with speculative and imaginative powers of the highest order; founder of the theory explaining the space rela- tions of atoms in molecules a theory which is essen- tial to a comprehension of the chemistry of organized and inorganized matter ; master in the field of dynamic chemistry; investigator and brilliant discoverer in the domain of the modern theory of solutions a theory which constitutes one of the greatest advances made by chemical science in the last quarter of a century: for these splendid and fertile achievements, by the xiii xiv PHYSICAL CHEMISTRY authority of the Board of Trustees of the University of Chicago, upon nomination of the University Senate, I confer upon you the degree of Doctor of Laws of this University, with all the rights and privileges appertain- ing thereunto. Professor van 't Hoff most cordially consented, not only thus to visit the United States as one of the guests of the University, but also, at the special request of the Department of Chemistry, to deliver a course of lectures on that branch of chemistry which owes so large a share of its recent develop- ment to his brilliant and profound investigations. The lectures were delivered in English, and, in slightly condensed form, are reproduced in this volume. The interest which they aroused was most gratifying both to the lecturer and to his hosts. They were attended by large audiences, which included professors of chemistry and related sciences from many distant states of the Union. Those who had the privilege of hearing them will not soon forget the genial personality of the speaker, the simple and lucid language, and the suggestive treatment which combined to make them memorable. The excellent portrait, a reproduction of which forms the frontispiece, will give added interest to the book. The plate showing a sheet of tin attacked by the "tin- disease" was made from a photograph kindly furnished by Dr. Ernst Cohen. ALEXANDER SMITH. CHICAGO, AUGUST, 1902. TABLE OF CONTENTS INTRODUCTORY PAGE LECTURE I 3 Kekule*'s View, that Thirty Years Ago Chemistry Had Reached a Dead Point Structural Chemistry Leads to Stereochemistry The New Physical Chemistry The Genius of Physical Chemistry Exhibited by Discussion of Osmotic ' Pressure Calculation of Osmotic Pressure from Temperature | and Concentration Applications of the Conception of Osmotic Pressure in Biology Loeb's Fertilization Experi- ment. PHYSICAL CHEMISTRY AND PURE CHEMISTRY LECTURE II 15 Plan of the Lectures Modern Physical Chemistry Distin- guished from the Earlier Physical Chemistry, and its Nature Defined It Rests on Two Foundations: the Extension of Avogadro's Law to Solutions, and Thermodynamics The Extension of Avogadro's Law The Thermodynamical Prin- ciple of the Conservation of Energy The Thermodynamical Principle of Carnot-Clausius Reversible Cycles Illustra- tions of the Application of These Principles The First Great Service of Physical Chemistry in the Field of Pure Chem- istry Application of a New and Comprehensive Principle for the Study of Inorganic Problems Case of Carnallite as Illustration Graphic Representation of the Results. LECTURE III - 31 The Second Great Achievement of Physical Chemistry in the Field of Pure Chemistry Berthelot's Principle of Maximum Work Many Facts Contradict It The New Conception that Change Occurs Only When Work Can Be Done The xv xvi PHYSICAL CHEMISTRY PAGE Methods of Determining Which Changes Will Be Able to Do Work The Thermochemical Method The Electrical Method The Third Great Achievement of Physical Chem- istry in the Field of Pure Chemistry The Theory of loniza- tion Qualitative and Quantitative Illustrations of the Use of This Theory. PHYSICAL CHEMISTRY AND INDUSTRIAL CHEMISTRY LECTURE IV - 45 The Co-operation of Physical and Industrial Chemistry Two Illustrations to Be Discussed Results of Scientific Study of Carnallite and Possibilities of Their Commercial Application to the Manufacture of Potassium Chloride The Recent Discoveries in Connection with Alloys and Steel, Introduced by a Description of the Peculiar Behavior of Tin, and its Explanation White and Gray Tin and Their 'Transi- tion Point at 20 The Methods of Determining the Transi- tion Point Use of the Dilatometer The Electrical Method. LECTURE V - 58 Results of the Physico-Chemical Study of Wrought Iron, Cast Iron, and Steel Complications Introduced by the Presence of Carbon and the Occurrence of Solid Solutions Method of Studying Iron by Polishing, Etching, and the Use of the Microscope Constituents are Ferrite, or Pure Iron; Marten- site, or the Solid Solution of Carbon in Iron; Cementite, or the Carbide of Iron; Graphite, or Free Carbon; Pearlite, or the Cryohydratic Mass Two Forms of Ferrite with Transi- tion Point at 850 Pearlite, a Mixture of Cementite and Fer- rite, and its Formation and Composition Hard Steel is Overcooled Martensite The Graphite The Behavior of Melted Iron Rich in Carbon Rapid Cooling Gives White Cast Iron Containing Much Cementite Slow Cooling Gives Gray Cast Iron by Decomposition of the Cementite and Pro- duction of Graphite, and Finally Pearlite A Numerical Illus- tration of the Behavior of Molten Iron Containing 6% per Cent, of Carbon When Cooled (1) Rapidly and (2) Slowly. 1 TABLE OF CONTENTS xvii PHYSICAL CHEMISTRY AND PHYSIOLOGY PAGE LECTURE VI - 73 ,*, The Theory of Solutions Based upon the Extension of Avo- gadro's Principle and its Importance in Physiology Osmotic Pressure and Osmotic Phenomena The Experiments of de Vries with Plant Cells The Work of Donders and Ham- burger with Blood Corpuscles The Experiment of Massart with the Human Eye and with Bacteria Loeb's Work on Artificial Fertilization The Measurement of Osmotic Pres- sure Observation of the Freezing Points for Determining Equality of Osmotic Pressure Specific Action of Ions in ? Physiology. LECTURE VII - 84 Enzymes, Their Preparation and Nature Enzymes as Cat- alytic Agents Chemical Equilibrium Graphic Representa- tion of Incomplete Chemical Interactions Incomplete Actions Occur When the Heat Change is Small Application to the Behavior of Enzymes Illustrations The Synthesis of Amygdalin. PHYSICAL CHEMISTRY AND GEOLOGY LECTURE VIII - 97 The Formation and Structure of Geological Salt Deposits Early Study of Deposition from Solutions Containing Several Salts, by Usiglio The Proportion of the Constituents as Well as Their Solubility to Be Considered The Modern Method of Study and Graphic Representation The Case of a Single Salt and Water at a Fixed Temperature, 25 The Case of Two Salts Simultaneously Present at 25 The Case of Three Salts at 25 The Problem of Sea-Water at 25, with All Salts Present. xviii PHYSICAL CHEMISTRY PAGE LECTURE IX 115 The Influence of Time and of Variations in Temperature and Pressure on Deposition The Time Factor and Delayed Crystallization Several Compounds, Found in Nature, Do Not Appear at All in Laboratory Experiments on Deposition, But Can Be Included in the Scheme by the New Method of Agitation with Solutions The Behavior at Temperatures above 25 New Minerals Formed above 25 and Absent at 25 New Combinations of Minerals Possible above 25 Disappearance above 25 of Minerals Formed at That Tem- perature The Influence of Possible Changes in Pressure is Too Slight to Affect the Results. INDEX 125 INTRODUCTORY 'v ". /'' ' J J ' J J < > J : ' LECTUKE I INTRODUCTORY Kekule"'s View, that Thirty Years Ago Chemistry Had Reached a Dead Point Structural Chemistry Leads to Stereochemistry The New Physical Chemistry The Genius of Physical Chemistry Exhibited by Discussion of Osmotic Pressure Calculation of Osmotic Pressure from Temperature and Concentration Applica- tions of the Conception of Osmotic Pressure in Biology Loeb's Fertilization Experiment. INASMUCH as during the next few days I am to deliver a number of lectures on certain topics of a physico-chemical nature, I should like to throw my address before this educa- tional conference into the form of an introduction to these lectures. I must begin by saying at the outset that one of our best modern historians of the science of chemistry, Ladenburg, 1 expresses the opinion that the most characteristic feature of the chemistry of the last fifteen or twenty years is the contin- ued increase in the prominence of this physical, or, as many say, general, chemistry. Will you allow me, therefore, briefly to explain how this physical chemistry has been developed, and what its present importance is, and will you permit me in doing so to refer to personal recollections to some extent ? Thirty years ago, when, as a young student in the University of Bonn, I first became acquainted with the sci- ence of chemistry, under the instruction of one of the most l Entwickelung der Chemie in den letzten 20 Jahren, Stuttgart, 1900. 3 PHYSICAL CHEMISTKY noted of chemists, Kekule", that science was pronounced by our master to have reached a dead point, and to be without visible prospect of new advance. At that time the belief in the existence of atoms, although only an indirect conclusion from chemical facts, seemed to be well-founded. The molecular theory, which had been chiefly developed in connection with physics, lent strong support to it. The details in regard to the relations of the atoms in the molecule were known, or at all events the attainment of this knowledge in the case of the more com- plex or newer substances was only a question of time. Thus, the formula of methyl alcohol was: H \ H C - O - H H/ This expressed the fact that in a molecule of this substance, four hydrogen atoms, each represented by the letter H, along with one atom of carbon and one of oxygen, repre- sented respectively by the letters C and O, were present, and that they were attached to one another in the manner shown by the connecting lines. Realistic as this conception was, it was very clearly recognized that such symbols were but mental pictures or diagrams on paper, and chemistry was looking for some Newton who should discover the laws according to which the atoms themselves were held together in their molecular configuration to form one complete whole. As we probably are all aware, however, no Newton of this kind arrived, and yet only a few years after Kekul6's INTRODUCTORY unfortunate utterance (a sort of remark, we may say in passing, such as a teacher ought perhaps never to make before his pupils) there arose the conceptions of stereo- chemistry, giving birth to a new, but now well-developed and vigorous, branch of our science. By means of stereochemistry so much at. least was accomplished that, the real existence of the atoms being assumed, not only was their mode of union described but also their relative positions in the molecule was determined. The above symbol for methyl alcohol now became a tri- dimensional model, with the carbon in the center of a tetra- hedron, at whose four equidistant points the three hydrogen atoms and the hydroxyl group were situated. We remained, however, and after twenty-five years still remain, unacquainted with the laws which control these relative positions. Perhaps, by the help of the new con- ception of electrons, we may be on the eve of getting a clearer knowledge of the condition of the atoms, at least in the neighborhood of the absolute zero of temperature. During these twenty-five years, however, investigation still proceeded, although in an entirely different direction. It did not advance by the elaboration of symbol archi- tecture, with atoms as the bricks. About fifteen years after Kekule"'s unfortunate expression, a second child of hope, the new physical chemistry, came into being. It did not arise all at once : there is hardly a branch of science in which this occurs. It was developed like a small plant, unseen in the shade; at length it feels the sun and promises to expand into a colossal tree. 6 PHYSICAL CHEMISTRY Some, like Duhem, 1 go so far as to claim for physical chemistry the rank of a third science, and range it beside the sciences of physics and chemistry. Others, like Winkler 2 and Ladenburg, favor the view that a prominent place within the territory of chemistry should be devoted to physical chemistry, and that the previous subdivision into organic and inorganic should be replaced by a division into three. In this connection, it is of interest to mention that at the present moment the University of Gottingen is planning to organize its chemical department on this basis. Leaving aside all principles of subdivision, which must always be of an arbitrary nature, since science, like that nature which it reflects, must be one great whole, I should like here to answer the question, What has this physical chemistry brought to pass? This question may be taken in either one of two ways, general and particular, and answered accordingly. One might, on the one hand, exhibit the general conclusions, and, taking this sense, I should have to speak of the laws of chemical change, of reaction speed, and of electrochemical processes. Yet even so I should be unable to do this without using complicated formulae, which the character of this introduction forbids. On the other hand, the genius of physical chemistry may be portrayed by a study of one of the special problems which it has been in a position to solve. It is in this direc- 1" Une science nouvelle : La chimie physique," Revue philomat ique de Bordeaux etdu Sud-Ouest, 1899. ZBerichte d. deutsch. chem. Gesell., Vol. XXXIV, p. 399. INTRODUCTORY tion that I prefer to proceed in answering the above ques- tion, and I shall ask your attention to one of the best known and most far-reaching achievements of physical chemistry. It is connected with the establishment and application of the conception of osmotic pressure. By way of approaching this special problem, consider the attraction for water shown by some well-known substances, like quicklime. If a bottle is filled up with this and is loosely stoppered, the lime will attract water from the moist air, will swell up, and, finally, no matter how strong the bottle may be, will inevitably break the vessel which con- tains it. An enormous force is developed by this attraction for water, so great that it has not been found pos'sible to subject the pressure to exact measurement. A similar but less violent phenomenon can be observed, and may be measured, provided we confine ourselves to dilute solutions. Thus, sugar, even in dilute solution, shows this attraction for water to a marked degree. We take, fol- lowing Pfeffer, 1 a one per cent, solution of sugar, and fill with it a vessel whose walls are porous, so as to permit the pas- sage of the water alone. A suitably prepared battery jar will serve the purpose. We place this, after closing it, in pure water, and find that the latter, attracted by the sugar solution, forces its way through the porous wall until at 7, if the vessel is sufficiently strong to withstand it, a pressure of two-thirds of an atmosphere is attained. This sort of pressure is called osmotic pressure. We can now proceed further to generalize, and say that l Oamotische Untersuchungen, Leipzig, 1877. 8 PHYSICAL CHEMISTRY J every substance capable of dissolving will attract the solvent. This is, in fact, only another way of referring to the ten- dency to dissolve. Conversely, the solid substance is in turn attracted by the solvent, and diffuses into it when it is furnished an opportunity to do so. In the latter case the osmotic pressure appears in another light, and becomes the pressure which prevents the undissolved molecules from freely moving into the surrounding solvent, when a state of saturation has been reached. After the same fashion, gas molecules exercise gaseous pressure in the direction of an empty space when they are hindered by a partition from entering it. This osmotic pressure was studied as early as a hundred years ago, especially with reference to its significance in physiological processes. It was found to have a definite value. This seemed, at first, to be dependent upon the nature of the membrane, to vary with the nature of the dissolved substance and of the solvent, to be obviously dependent upon the concentration, and likewise to be very sensitive to change of temperature. These were essentially the facts known about osmotic pressure up to the time at which the path being blazed by physical chemistry encoun- tered it. The result was unexpectedly simple. So plain was it that now one can even calculate the osmotic pressure (for a dilute solution of a non-electrolyte) when the concentration and temperature are given. The whole relation is, in fact, presented in the expression INTRODUCTORY 9 in which P is the osmotic pressure in atmospheres, T the absolute temperature, and C the concentration or the num- ber of gram- molecules of the dissolved body per liter of solution. The numerical value of Pfeffer's observation upon the one percent, solution of sugar, in which T== 273 -f 7 or 10 280 and C = oTn > is obtained at once from the above formula. I should like to emphasize the differences in the methods of physical chemistry and its manner of procedure when compared with those of stereochemistry. The former does not primarily seek the solution of its problems in any con- ception of the nature of matter. The above formula contains, so far as this is concerned, only the relative molecular weight, which, where investigation in the form of a gas is possible, corresponds to the gas density. Physical chemis- try therefore confines itself to numerical relations between directly measurable magnitudes. In spite of the limitation which physical chemistry thus imposes upon itself, it is certainly a strong evidence of its sound foundation and healthy power to develop that it shows itself, in a continually increasing degree, capable of solving those problems which, on account of their direct relation to life, seem to be the most complex. If we take into con- sideration the colossal labors which were spent in the service of atomic conceptions, it must be admitted that relatively little has been accomplished by them in this particular direction. The very opposite can be stated of the labors of the physical chemist. As long as ten years ago, in Utrecht, 1 lu Over de physiologische beteekenis der jongste stroomingen op chemisch physisch gebied," Natuur- en Geneeskundig Congres, Utrecht, 1891. 10 PHYSICAL CHEMISTRY I employed an opportunity like the present to refer to the tremendous r6le which osmotic pressure, whose laws have been laid bare by physical chemistry, plays in many of the processes of living organisms. At that time I was able to present the results of several physiological investigations, which tended to show that osmotic pressure is a fundamental factor in the most various life-functions of animals and plants. According to de Yries ' it regulates the growth of plants. According to Bonders and Hamburger 2 it regulates the functions of the red blood cor- puscles, and thus of the blood. According to Massart 3 it con- trols some of the functions of the human eye, as well as the life of the seeds of disease, and deadly organisms like the bacilli of typhoid fever. Since that time the literature of this subject has grown until it would easily fill a large and comprehensive volume. 4 Perhaps the most pregnant fact of all is that which has been established in this very University of Chicago by Loeb. It is to the effect that the act of fertilization of lower ani- mals, like sea-urchins, can be in part replaced by a definite increase in the osmotic pressure of the liquid in which the unfertilized egg is lying. The development starts and even i u Eine Methods zur Analyse der Turgorkraft," Pringsheims Jahrbucher, Vol. XIV. 2 Onderzoekingen gedaan in het physiologisch Laboratorium der Utrechtsche Hoogeschool, (3), Vol. IX, p. 26. 3 Extrait des archives de biologie, Liege, 1889. * A compilation extending to 1900 is given by KOEPPE, Physikalische Chemie in der Medizin, Wien, 1900. See also the very full bibliography in BURTON E. LIVING- STON'S Rdle of Diffusion and Osmostic Pressure in Plants, University of Chicago Press, 1903. INTRODUCTORY 11 proceeds to the production of a motile organism. I may most fitly conclude in the words with which the investiga- tor just named closed an address 1 given on the present subject : "At no time since the period immediately following the dis- covery of the law of conservation of energy has the outlook for the progress of physiology appeared brighter than at present, this largely being due to the application of physical chemistry to the problems of life." 1" The Physiological Problems of Today," American Society of Naturalists, Ithaca, 1897. PHYSICAL CHEMISTRY AND PURE CHEMISTRY LECTURE II PHYSICAL CHEMISTRY AND PURE CHEMISTRY Plan of the Lectures Modern Physical Chemistry Distinguished from the Earlier Physical Chemistry, and its Nature Defined It Rests on Two Foundations, the Extension of Avogadro's Law to Solutions and Thermodynamics The Extension of Avogadro's Law The Thermodynamical Principle of the Conservation of Energy The Thermodynamical Principle of Carnot-Clausius Reversible Cycles Illustrations of the Application of These Principles The First Great Service of Physical Chemistry in the Field of Pure Chemis- try Application of a New and Comprehensive Principle for the Study of Inorganic Problems Case of Carnallite as Illustration Graphic Representation of the Results. I WILL begin by setting before you the scheme of that which I desire to develop in these lectures. I have divided the material into four parts, each of which refers to physical chemistry, but gives a view from a different standpoint. The object of this is to show the relations to, and the influence upon, different branches of science, pure or applied, which physical chemistry is able to exhibit. I should wish to consider physical chemistry, in the first place, in its application to pure chemistry, and, in the second place, in its relation to applied or technical chemistry. Then I shall devote two lectures to the relation of physical chem- istry to physiology, since the characteristic of the develop- ment of physiology in recent years seems to lie in the fact that it has made application of physico-chemical methods. 15 16 PHYSICAL CHEMISTRY Finally, I should like to show by a few examples how physi- cal chemistry attempts to attack geological problems. Beginning with the relation between physical chemistry and pure chemistry, I must first briefly delimit that which at the present day we understand by the former title. If we take the expression in its most general sense, it refers evi- dently to the application of physical expedients, methods, and instrument's to chemical problems. Interpreted in this way, one might state that when Lavoisier made chemistry the science which it is, he simultaneously founded physical chemistry. He did this inasmuch as he applied the balance, obviously a physical instrument, to the testing and establish- ing of fundamental laws in the realm of chemistry. Later, when Bunsen, in his universally-known investigations with the spectroscope, determined the composition of the sun and stars, it could be said with equal right that physical chemis- try was involved, since the spectroscope is classed as a piece of physical apparatus. In this way ever greater advances in our science have been bound up with the intro- duction of physical methods of observation and measure- ment. Apart from this, it is said, and said correctly, that physi- cal chemistry is a recent development of the last fifteen years. 1 I should like to explain in what way this last phase in its development may be considered as having especially profound significance. The introduction of the spectroscope by Bunsen, and the later employment of the calorimeter in i NEBNST, Address at the Opening of the Institute of Physical Chemistry and Electro-chemistry, GOttingen, 1896. PURE CHEMISTRY 17 the chemical laboratory by Berthelot and Thomson, were of the highest importance, but were limited to a particular mani- festation, such as the emission of light or the production of heat. Now, what physical chemistry in the latest period has done, or has claimed to do, did not consist in the introduction of new apparatus or of a new method of observation. The most recent development of physical chemistry has been char- acterized rather by the establishment of comprehensive prin- ciples which fertilize the whole foundation of the science, and promise to furnish nourishment for a large part of the chem- istry of the future. I should be glad if I could exhibit one of these fundamental principles in application before you in the same manner as a lecture-experiment is shown. Yet this practical procedure is precisely that which the character of the new development expressly excludes, since it has not brought into use essentially new apparatus and methods, but rather new laws, which are unfortunately not of the sim- plest description. I remember very well that as a student I was never able to understand the real import of Avogadro's law, and that I received the first glimpse of its bearing when I explained it in teaching and applied it in experiment. And yet the prin- ciples which I have to lay before you are still further removed by their abstract character from the range of every- day thought than even the law of Avogadro. If, therefore, I were to attempt to build up these principles from their foundations, those to whom they were new would probably find their time had been wasted, since they would have no opportunity for gaining a correct understanding of them by 18 PHYSICAL CHEMISTRY FIG. i actual application. On the other hand, those to whom these principles are already known might justly complain that nothing new had been set before them. Thus I have considered it most advisable not to enter upon the study of these principles very deeply, but to -assume them as known. I shall prefer to take for detailed consid- eration the application of these principles to the answering of definite questions, and thus, so far as possible, to break new ground. There are in the main two foundations on which the recent development of physical chemistry rests: the extension of the law of Avogadro and thermody- namics. The particular extension of Avogadro's law referred to may easily be connected with the con- tent of the original rule when the latter is expressed in the following form: If we take a fixed volume (Fig. 1) of any gas, for example, oxygen, then we know that it exercises a pressure upon the walls of the vessel. This pressure, probably pro- duced by the impact of the molecules, may be measured by a manometer such as that shown in the figure. Its value depends upon the temperature and we may assume this to be recorded by the thermometer and to be, for example, 20. Now, Avogadro's rule states that if into an equal space (Fig. 2) we introduce so much of another gas, for example carbon dioxide, that at the same tempera- FIG. 2 PURE CHEMISTRY 19 ture (20) an equal pressure is exercised, then both spaces must contain equal numbers of molecules of their respective gases. We might consider this number to be 1000 in each case. The absolute number is unknown and only the equality in the number is postulated. The expansion of this principle is concerned with solu- tions. In these also an effect comparable with gaseous pressure is exercised. The gaseous pressure has to do with the fact that a gas endeavors to diffuse into a vacant space and thus presses upon the impermeable walls, which prevent its further progress. In the same way, in a solution, also, the dissolved substances tend to diffuse into the pure solvent when the solution and solvent are in contact. This may be seen when the liquids are carefully placed one above the other in the same vessel in such a way that that which is specifically lighter is placed upon the top. A partition, impermeable by the dissolved body, which did not interfere with contact between the solution and the solvent (which, in other words, was permeable by the solvent), would restrain this diffusion and experience a pressure. This pressure is obviously the so-called osmotic pressure which has already been mentioned (p. 7) in the introduction. The extension of Avogadro's principle consists in this: that for a given sub- stance the osmotic pressure is equal in value to the gaseous pressure, provided the temperatures and the concentrations, that is, the quantities in unit volume, are the same. From this it follows immediately that two solutions of different bod- ies containing equal numbers of molecules in equal volumes, provided they are at the same temperature, exercise the 20 PHYSICAL CHEMISTRY same osmotic pressure. Not only so, but when the molecular weight is known, this pressure, like the gaseous pressure, can be calculated with ease. For our purpose, it is unneces- sary to pursue this law by further numerical illustration. We shall add only that this law of Avogadro and its extension (and be it remarked, the extension is a most com- prehensive one, since it applies to all soluble bodies and to all solvents) is restricted in its application within certain limits. It claims strict accuracy, both in the original and extended forms, only when the dilution is very great, or, in other words, only under conditions which cannot be realized practically. Nevertheless, at dilutions which correspond to that of atmospheric air, that is to say, in the case of gases at a pressure of one atmosphere and in the case of solutions of an analogous concentration (about one-tenth normal), the deviations, in most cases where the principles find applica- tion, are insignificant. So much for the first principle which has contributed to the recent development of physical chemistry, and is often named the theory of solutions. The second concerns the application of thermodynamics, and particularly of the law of conservation of work or energy, and of the Carnot-Clausius principle to chemical questions. What I said in the begin- ning about Avogadro's law, to the effect that the correct appreciation of its content can be reached by most students only after application to definite problems encountered in independent research, might be said perhaps with even greater truth of the principle which is now to be discussed. The principle of the conservation of energy is in itself PURE CHEMISTRY 21 simple enough. No energy arises or disappears. Change in form in an unchanging amount is alone possible. The forms with which we have to do in the treatment of chemical problems are in the main mechanical work, heat, light, and electrical energy. The whole preliminary knowledge required consists in knowing that when mechanical work is converted into heat 425 kilogram-meters give exactly one calorie ; when electric energy is turned into heat, one gram-equivalent at a tension of one volt gives 23 calories. The Carnot-Clausius principle is far from simple. This conception, again, I never understood until I had occasion to apply it in my investigations, and to test it in numerical calculations. While Avogadro's law can be stated in few words, this is impossible in the present case. Further, the principle of Carnot-Clausius finds expression in so many different forms that even after practice it is not very easy to handle. Since it is possible that among the younger students of science present there may still be some who have yet to take their first step into this region by applying its conceptions to chemical problems, I shall make a suggestion as to the choice of the most suitable form of this principle. It may be applied by carrying out so-called reversible cycles of operations or by the introduction of abstract physical conceptions and mathematical functions, such as entropy, as is done by physicists like Gibbs, Planck, and Duhem. I am convinced that, for the chemist, the first form, in which reversible cycles are employed, is the most advantageous. The difficulty that is then encountered is confined to the conception of a "reversible cycle." 22 PHYSICAL CHEMISTRY Briefly stated, a cycle consists in a series of changes in course of which the original condition is reached. Thus, for example, we permit ice to evaporate, condense the vapor to water, and then freeze the water. These changes are reversible, provided they take place under such conditions that the change can proceed in either direction. This is true, for example, when water is frozen in a region where the temperature is C., and where, therefore, ice can just as well melt. At temperatures above or below only one or other of these processes can take place. Now, in such a cycle of operations and this is the content of the Carnot- Clausius principle the sum of the quantities of heat (), divided by the absolute temperature (T) at which it is com- municated, is equal to zero. A very simple application which frequently throws an unexpected light on chemical problems is to be noted when the reversible cycle is carried out at constant temperature. Here the equation obviously becomes: That is to say, the sum of the heats communicated is equal to zero, or, in other words, no heat passes into any other form of energy, such as, for example, mechanical work. The sum of the work (A) accomplished in the course of the operations is, therefore, likewise zero. PURE CHEMISTRY 23 Applying this, for instance, to the above cycle with ice- water and vapor, we draw at once the important conclusion that at the vapor tension of water and ice must be equal. Considering processes more closely allied to chemistry such as the reversible change of rhombic and monoclinic sulphur at 96, and that of cyamelid and cyanuric acid at 150 we infer that there must be equality in each case between the vapor tensions of the two forms of sulphur, and between the so-called dissociation pressures of cyamelid and cyanuric acid at the point of change into gaseous cyanic acid. In the latter case we encounter another great advantage in the application of the Carnot-Clausius principle. This is that the complexity of the nature of the process under considera- tion does not introduce the slightest difficulty. The com- position of the bodies, for example, is of so little importance that atomic and molecular conceptions need not be consid- ered, and, strictly speaking, in the last-mentioned case, it need only be known that cyanuric acid, cyamelid, and cyanic acid have the same percentage composition, since otherwise the cycle of operations could not be carried out. I must limit myself to the foregoing brief remarks on the principles of Avogadro and Carnot-Clausius, and proceed to lay before you what is attainable by their application. In doing this I must first refer to those who, few in number and not always working under the most favorable conditions, during the last fifteen years have brought physical chemis- try to its present state of development. The very first place must be given to Ostwald, who by his comprehensive activity as a teacher, his astonishing literary labors, and his powers 24 PHYSICAL CHEMISTRY of organization has perhaps done more than any other for the spread of physical chemistry. I name along with him Arrhenius, whose introduction of the theory of electrolytic dissociation, and Nernst, whose application of the same theory, have opened up an entirely unsuspected field in the region of electric phenomena. The greatest progress is promised and the greatest prog- ress has been achieved by the application of physical chem- istry to that part of the science which is usually designated inorganic. This includes all the elements save carbon, whose chemistry, as you know, is classed as organic. That new principles ultimately to be applied to the whole science are more easily introduced in connection with the former, depends on the simpler character of inorganic problems. Inorganic elements, like potassium and chlorine, give usually a single compound, like potassium chloride. When the ele- ment carbon (C) is taken into consideration, however, this is all changed, and the combination of this element with hydrogen (H), for example, offers a seemingly innumerable number of possibilities, such as CH 4 , C 2 H 4 , C 2 H 2 , etc. Glancing at what has been achieved in inorganic chemis- try, three advances may be noted. First, it may be said that physical chemistry, in the handling of inorganic problems, has introduced an entirely new and comprehensive method of work. Secondly, we are in possession of a principle which enables us to foretell in what direction and how far a chemical change will proceed. Thirdly, physical chemistry has thrown new light on the nature of the solutions of the so-called electrolytes ; that is to say, of bases, acids, and salts. PURE CHEMISTRY 25 I hope to have the opportunity of illustrating each of these three achievements by describing a particular case. In order first to bring before you the new mode of treating inorganic problems, I shall describe its application to the study of carnallite, a mineral of technical importance, and known to be a compound (double salt) of magnesium chlo- ride, potassium chloride, and water. Let me add that the investigation in question was carried out in co-operation with Meyerhoffer, but that the method of treating inorganic compounds which is illustrated by it was originally developed more particularly by Bakhuis-Roozeboom. If you look up the subject of carnallite in the earlier text-books you will find the formula MgCl 2 .KC1 .6H 2 O, with the statement that the compound is colorless and crys- talline, and that it dissolves in water easily, with separation of potassium chloride. You will find also the method of preparation, and some further single, disconnected data. The new method of studying the subject leads, however, to a completely exhaustive knowledge of the subject. It is based essentially on a better comprehension of the equilib- rium relationships in complex chemical phenomena, and of the influences which temperature, proportions of material, and pressure exercise upon them. We have, for example, discovered so-called transition temperatures in complicated chemical changes, which have the closest resemblance to simple physical melting-points. Thus, according as one passes above or below this temperature, a complete change in one direction or the other takes place. This change is, however, of a complex chemical nature. We have dis- 26 PHYSICAL CHEMISTRY covered the phase-rule in terms of which the most dif- ferent sorts of equilibria can be uniformly interpreted. Finally, we have made easier, and in some cases for the first time made possible, the achievement of a know- ledge of the whole circumstances of a chemical change in relation to temperature and pressure, by an extensive application of graphic methods. Carnallite presents an especially good example of the last, and I should like par- ticularly to call your attention to the fact that a very mini- mum of observations puts us in possession of a complete knowledge of its whole behavior. The problem before us is this: Carnallite being a com- pound of magnesium and potassium chlorides and water, what arises when these three substances are brought together in different proportions, at different temperatures, and the escape of the water is prevented ? It is needless to add that all these conditions are easily realized in experimental work. In considering this question we shall start from the beautiful transformation which carnallite undergoes in pres- ence of water when the temperature is lowered. If the amount of water added is not too great, a part of the carnallite is dissolved, some potassium chloride separates in solid form, and a corresponding excess of magnesium chloride is found in the solution. When the temperature is now lowered the dissolved quantities vary on account of changes in solubility. About 21, however, a partial solidification of the liquid, akin to freezing, begins. This change resembles freezing also, in the fact that, in spite of PURE CHEMISTRY 27 continuous removal of heat, a thermometer shows that the temperature remains constant at 21. The same con- stancy is observed when heat is added, while melting of a greater or less proportion of the solid part takes place. Approaching the study of the phenomenon more closely, we find that the carnallite at this temperature decomposes as heat is removed, and that water is taken up, according to the equation : . 12H 2 O+KC1 . At 21 equilibrium exists between these two conditions, just as at the same relation subsists between water and ice. On each side of this temperature one or other is alone stable. This relationship may be expressed by writing the equation in the form: MgCl 2 . KC1 . 6H 2 + 6H 2 ? MgCl 2 . 12H 2 O -f KC1 . 21 This statement, however, does not include all the facts in regard to the phenomenon, since the water in contact with the carnallite and the two other bodies has dissolved some of each substance, and the composition of this solution is expressed by the formula : [H 2 + 0.066MgCl 2 + 0.005KC1]. Thus the exact equation has the following form: 0.208(MgCl 2 . KC1 . 6H 2 O) + 6[H 2 O + 0.066MgCl 2 + 0.005KC1] = 0.604(MgCl a . 12H 2 0) + 0.238KC1 . When these proportions are employed, below 21 com- 28 PHYSICAL CHEMISTBY plete solidification takes place, while above it only potassium chloride and solution remain. Viewing the system in relation to this chemical change, it must now be remarked that the solution which is there present, and whose composition has just been given, is the starting point of three series of saturated solutions which are obtained by changing the proportions of the materials. If, in the first place, we take somewhat more water, then even when the temperature is lowered the solution remains. It is saturated with MgCl 2 . 12H 2 O and potassium chloride, and has a definite composition peculiar to each tempera- ture. We shall note this composition only at the point where a new transformation occurs. This is at 34, where ice is formed. Here everything becomes solid, and the liquid disappears. At this point the composition of the solution is [H 2 O'+0.043MgCl 2 +0.003KC1] . If we now follow the relations at higher temperatures, two limiting cases are possible, according as an excess of MgCl. 12H 2 O or of KC1 is present along with the carnal- lite. In the former case we encounter at 17 the melting point of MgCl 2 . 12H 2 O; in the latter at 168 that of the carnallite. Time does not permit us to pursue the consideration of the subject in further detail, but it is obvious from what has been said that the conditions for the formation and existence of carnallite can be gradually delimited. In temperature they must lie between 21 and 168, and between these points the solutions from which carnallite is formed may PURE CHEMISTRY 29 have a maximum content either of magnesium chloride or potassium chloride up to saturation with either. Thus we find a region in which its existence is possible, and this region is capable of graphic representation. Three axes are obviously required : one for the tempera- FIG. 3 ture, OX (Fig. 3), and two others for the amounts of MgCl 2 and KC1 in the saturated solution, which are designated OY and OZ respectively. It is the composition of this solution that determines the nature of the solid bodies which will come out. Our transition temperature and the correspond- ing composition of the solution are represented by the point E. The three solubility curves proceeding from this point are ED, terminating in the freezing-point of the solution at 30 PHYSICAL CHEMISTRY D; EF, with the melting-point of MgCl 2 . 12H 2 O at F; EM, with the melting-point of carnallite at M. The whole car- nallite area is bounded by EFGHTKM. Within this lie all the possible methods of forming it by employment of the simple components ; on passing outside this area we encounter all the possibilities of partial or complete decomposition. The rest of Fig. 3 has been obtained by the addition of data of a simpler kind which fit into the scheme as follows : In the plane XOZ lies the solubility curve of potassium chloride, CP, which marks the limit of the deposition of potassium chloride from pure water. Since the line DEM corresponds to the presence of the maximum amount of mag- nesium chloride, a potassium chloride area arises which is limited on the left by the boundary PCDEM. Similarly, a magnesium chloride area fits into this, complicated by the occurrence of various hydrates, which is bounded on the left by the line BFiFED. An ice area closes the whole on the left and connects the three cryohydric points, B, C, and D, with A, which represents the freezing-point of pure water. LECTURE III PHYSICAL CHEMISTRY AND PURE CHEMISTRY The Second Great Achievement of Physical Chemistry in the Field of Pure Chemistry Berthelot's Principle of Maximum Work Many Facts Contradict It The New Conception that Change Occurs Only When Work Can Be Done The Methods of Determining Which Changes Will Be Able to Do Work The Thermochemical Method The Electrical Method The Third Great Achievement of Physical Chemistry in the Field of Pure Chemistry The Theory of lonization Qualitative and Quantitative Illustrations of the Use of This Theory. THE second service of physical chemistry to pure chem- istry depends on the fact that it has established the funda- mental principle which enables us to predict from other data whether a given chemical change will take place or not. When this chemical change is one which reaches a condition of equilibrium, as is often the case, then the principle per- mits also the prediction of the extent to which the change will go. You may be aware that a principle of this kind was stated by Thomson and by Berthelot, and received from the latter the name of principe du travail maximum. This principle was a very simple one, since it stated merely that the heat which is developed by a chemical change indicates the direction in which the change will proceed : when the possibility of evolution of heat exists, then the reaction will proceed in such a direction as to bring this about. Take, 31 32 PHYSICAL CHEMISTRY for instance, hydrogen and oxygen. Two grams of the former with sixteen grams of the latter can develop 69 calories when uniting to form water. The principle just referred to sees in this possibility of heat development the cause of the formation of the water, which, as we know, takes place when the mixture of the gases is ignited. Con- versely, if we consider nitrogen and chlorine, we find that by their union no heat will be developed; on the contrary, heat will be absorbed. So here, instead of a union of the elements, the tendency is toward the decomposition of the compound. When the union has been achieved by indirect means, decomposition can be brought about by the slightest shock. For many years this conception was a fundamental principle of thermochemistry, and numberless facts were known to support it. In spite of this it is not difficult to furnish examples of cases in which chemical changes take place with absorption of heat. Freezing mixtures, like that of hydrochloric acid and Glauber's salt, whose operation depends on the accom- plishment of a chemical change, in this particular case Na 3 S0 4 . 10H 2 + 2HC1 -> 2NaCl + 10H 2 O -f H 2 SO 4 , indicate the location of facts which contradict this "principle of maximum work." The greater number of reactions which proceed only to a certain limit, like the decomposition of calcium carbonate which ceases when a certain pressure of carbon dioxide has been obtained, likewise involve dis- proofs of the suggested principle. Nevertheless, the expression "maximum work" was for- PURE CHEMISTRY 33 innately chosen, since the correct principle for the prediction of reactions must connect the possibility of a change with the possibility of a concomitant accomplishment of work. The newer conception is not less simple than the older, and is in a measure self-evident. Whenever any change whatever in the realm of nature can accomplish work, that is, can over- come resistance, it must proceed when the resistance is absent. This is true in particular of chemical changes. Now, it must be noted that the accomplishment of work and the development of heat in chemical changes do not mean quite the same thing. Often they do go hand in hand, as in the case of explosives like gunpowder and dynamite. These materials are familiarly known to furnish by their explosion great chemical means of doing work and at the same time to develop large quantities of heat. A compound like phosphonium chloride (PH 4 C1), however, a solid body, tends to decompose at ordinary temperatures into the gases phos- phine (PH 3 ) and hydrogen chloride (HC1) with marked absorption of heat. Yet the decomposition products of this action may exercise a pressure of some twenty atmospheres. Here we have a case where the possibility of accomplishing work does not coincide with the capacity to develop heat, and yet where it is obviously the capacity to do work which controls the direction of the change. The great difficulty in applying this new principle to the prediction of reactions lies, however, in finding a method for determining from other data the existence of the possi- bility of accomplishing work and the amount of this work in any given action. We know that Berthelot devoted half 34 PHYSICAL CHEMISTRY of his life to the systematic measurement of heats of reac- tion. Trusting in his principle he desired to present chem- ists with the data which appeared from this point of view to be suitable for the prediction of chemical changes. Since a change in the fundamental conception itself, however, has been shown to be necessary, another magnificent life work has been suggested. This piece of research would require the repetition of all the investigations, carried out by Berthelot with the calorimeter, with the object of determining the ability of each reaction to do work. This task would be, however, incomparably more difficult than Berthelot's, since the possibility of accomplishing work depends in a much greater degree on the conditions, the temperature, and, in the case of dissolved bodies, the concentration, than does the heat development. This fact is in harmony with the great influence which these factors exert upon chemical changes. Let us begin with a very simple example and consider the formation of carnallite at 21 according to the simplified equation : MgCl s . 12H 2 O + KC1 = MgCl 2 . KC1 . 6H 2 O + 6H 2 O. Obviously, at 21 the possibility of doing work (E) of which the formation of carnallite is capable, is zero. E = Q. Above 21 the reaction proceeds, however. It can, therefore, overcome a resistance, and since the reaction is accompanied by increase in volume this resistance might be a pressure. The maximum work will obviously be obtained PURE CHEMISTRY 35 in this case if the resistance is so great that the formation of carnallite is just able to take place and no more, while any increase in the pressure would cause a reversal of the change. Under these circumstances the transformation is reversible, and thus the principle of reversible cycles can be applied to it. The use of this principle leads to the expression dE= -W^- or for finite values This means that at a temperature d T (or A) degrees above the transition point, which in the present case is situated at 252 on the absolute scale, an amount of work dE (or E) can be accomplished. In applying this formula, since W is the heat of formation of carnallite by the action repre- sented in the preceding equation, dE and W must be expressed in the same units, for example calories. From the above expression the most essential fact may be read at once. At the transition temperature (A = 0) E has the value zero. Above and below this the sign of E changes. Here the sensitiveness to changes in tempera- ture of the power to do work is most pronounced, and the sensitiveness of the direction of the chemical change to the same influence is most noticeable. The principle of Berthelot now appears in a new light. If A/ = T, that is to say, if the absolute zero is the tem- perature of experiment, then E=W . 36 PHYSICAL CHEMISTRY That is to say, under these circumstances, the heat developed will be a measure of the capacity to do work. The fact that Berthelot's principle under ordinary conditions so frequently gives satisfactory results depends chiefly on the fact that our ordinary temperature of experiment is relatively low, being only 273 degrees removed from the absolute zero. In the neighborhood of such a temperature as 1000 the whole cir- cumstances are essentially different and usually the results are in conflict with Berthelof s law. Thus at that tempera- ture acetylene is formed with absorption of heat, and water decomposes in spite of the fact that its formation is accom- panied by the evolution of heat. We must also point out a second basis for the measure- ment of capacity for doing work which has been extremely fruitful. The relation of this capacity to do work to the pos- sible accomplishment of mechanical work has already been referred to. Then we noted its relation to heat development. There remains still for consideration its relation to the pro- duction of electricity. Take a chemical change which develops electricity, like the displacement of copper by zinc in the Daniell cell, Zn -f CuSO 4 - ZnSO 4 + Cu . This reaction can just as well be overcome by a suitable resistance and forced to proceed in the reverse direction, as an action accompanied by increase in volume can be reversed by pressure. Here, however, the opposing force must be of an electrical nature. As a matter of fact, when a current of electricity is applied in the reverse direction to a Daniell PURE CHEMISTRY 37 cell the amount of chemical change is at once diminished. The change can be brought to rest completely if the electro- motive force of the contrary current is equal to that of the cell ; and if it is greater the direction of the action may even be reversed. The electromotive force when electricity is pro- duced corresponds therefore to the pressure when the chemi- cal change tends to bring about an increase in volume. Detailed consideration from this point of view leads us to discover in the electromotive force a measure of the capacity to do work. In all this we have a very rich field for working out the problem of predicting reactions, and this method brings within our grasp the prediction of reactions which are much less simple than those which, like the formation of carnallite, are characterized by a transition temperature, and whose whole behavior is defined when a single temperature is given. In this way, too, the more delicate, gradual displacement of a condition of chemical equilibrium under the influence of temperature and concentration is brought under control a fact which has recently been demonstrated in a most striking manner. 1 A chemical change which illustrates this is the action of thallium chloride on potassium sulphocyanate solution. This takes place with so-called double decomposition according to the equation: T1C1 + KSCN = T1SCN + KC1 . This change belongs, however, to those which reach a con- dition of rest before they have been completely accomplished, i BBEDIG UND KNCPFFEB, Zeit.f. phystk. Chem., Vol. XXVI, p. 260. 38 PHYSICAL CHEMISTRY and lead to a so-called chemical equilibrium. This we repre- sent in symbols thus: T1C1 + KSCN 5 T1SCN + KC1 . The condition of equilibrium exists not only at a definite temperature, as in the case of equilibria having transition points, but, as the temperature changes, is displaced grad- ually in one direction or the other with a corresponding alteration in the concentrations of the dissolved chloride and sulphocyanate of potassium. The above change was employed for the construction of a galvanic cell, whose electromotive force was measured. The changes in this electromotive force brought about by altera- tions in temperature and concentration were studied. From this investigation the conditions were discovered under which the electromotive force became zero. In view of the small solubility of the thallium salts, this depended essentially on the concentration of the chloride and sulphocyanate of potas- sium. In a simultaneous study of the conditions when chemical equilibrium was reached, it was discovered that they corresponded exactly to those at which the electromo- tive force became zero. We were thus furnished with the sharpest possible test of the principle involved. We come now to the third achievement of physical chem- istry in the realm of pure chemistry. This has to do with the nature of the solutions of acids, bases, and salts. These have been called electrolytes, since they conduct electricity, and since the dissolved substance is decomposed into two so- called ions. At the one pole acids give hydrogen, while at the other (the positive) . the rest of the molecule is set free. PURE CHEMISTRY 39 This ion in the case of oxygen salts usually decomposes with evolution of oxygen. For example: CuSO 4 = Cu + SO 4 , and SO 4 = SO 3 -f O . The application of Avogadro's law as extended to solu- tions, especially dilute ones, has had curious consequences in the case of electrolytes. It appears that the number of dissolved molecules is greater than that corresponding to the smallest possible chemical formulae, such as CuSO 4 or HC1 in the above examples. This excess in the number of molecules forces us almost irresistibly to the belief in a genuine decom- position. In the case of salts, a priori considerations might lead us to the inference that in their solutions a mixture of the acid and base would be found. If this were the case no heat change would be perceptible when the acid and base in suitably diluted form were mixed, since no formation of salt should result. As a matter of fact, however, experiments show that a notable production of heat actually occurs. Then, too, this explanation is obviously inapplicable to the solution of an acid or of a base by itself. A fortunate release from this dilemma was suggested by Arrhenius in the assumption of electrolytic dissociation. This assumption consists, as is well known, in the idea that the ions which are liberated when the solution is decomposed by electricity are all present in the free condi- tion before the application of the current. Their presence is not perceived, in consequence of an electrical charge which is attached to them and which they lose during electrolysis. Thus, in dealing with hydrochloric acid, we 40 PHYSICAL CHEMISTKY can see that the dissolved body is not HC1, but a mixture of H and Cl, that is to say, of positively charged hydrogen and negatively charged chlorine atoms. That these charges of electricity should so profoundly alter the behavior that neither the familiar properties of hydrogen nor those of chlorine are perceptible in the hydrochloric acid solution, appears at first sight to be a serious objection. On closer consideration, however, we see that this conception may be accepted as a possibility, even if the difficulties have not been completely cleared up. Over against this ground of hesitation we are in a position to set a great number of facts which before the assumption of electrical dissociation were without explanation. Not only so, but this theory has enabled us to foretell chemical occurrences and to some extent account for them mathematically. It may be added that Raoult, who has devoted himself for more than twenty years to the study of dilute solutions, at first rejected this theory, but now fully concurs in the explanation offered by Arrhenius. If it is a question of facts of a qualitative nature, one has only to put forth his hand in any direction. Thus, chlorine as it is contained in electrolytes, such as solutions of hydrochloric acid and its salts, which according to this theory contain it in ionic form, behaves in an entirely differ- ent manner from the element as it is found in compounds of a different sort, like chloroform and chloral. The former with silver nitrate give silver chloride at once, the latter do not. Again, the identity in the color of the different salts of rosaniline, whether we take the nitrate, hydrochloride, or any other, finds its explanation at once in the presence of PURE CHEMISTRY 41 the same colored ion. The smallest change in this colored ion, however, by the introduction of methyl, for example, produces profound and much prized changes in tint. Still again, the equal optical rotations of solutions of the various salts of tartaric acid may be accounted for by the fact that they contain the same optically active ion, while a change in this ion itself, by the introduction of acetyl, for example, produces instantly a marked change in the extent of the rotation. The results of quantitative measurement are not less con- vincing, although unfortunately always limited by the fact that the foundation of the calculations, the extended law of Avogadro, is strictly applicable only to the condition of extremest dilution. The limits of time forbid our pursuing the subject in greater detail in this direction. I simply mention the calculation of diffusion speed by Nernst, the calculation of the variation in the conductivity of distilled water with temperature by Kohlrausch, and the calculation of the influence of concentration on the behavior of organic acids and bases by Ostwald. A representative compilation of the achievements in this direction was presented by Arrhenius to the International Congress of Physicists, held at the Paris Exposition of 1900. Finally, let me add that the liquid in which the life functions of living plants and animals are performed is invariably a dilute electrolyte. For this reason physiology and medicine have promptly taken possession of these new conceptions and the consequences even of their earliest applications have been most significant. PHYSICAL CHEMISTRY AND INDUSTRIAL CHEMISTRY LECTURE IV PHYSICAL CHEMISTRY AND INDUSTRIAL CHEMISTRY 1 The Co-operation of Physical and Industrial Chemistry Two Illustra- tions to Be Discussed Results of Scientific Study of Carnal- lite and Possibilities of Their Commercial Application to the Manufacture of Potassium Chloride The Recent Discoveries in Connection with Alloys and Steel, Introduced by a Description of the Peculiar Behavior of Tin and its Explanation White and Gray Tin and Their Transition Point at 20 The Methods of Determining the Transition Point Use of the Dilatometer The Electrical Method. IN this and the' following lecture I purpose dealing with the application of physical chemistry to technical problems. In a general way, it may be said that since physical chemistry makes it possible to treat the problems of pure chemistry in a new manner with fruitful results, it follows almost of necessity that this influence of physical chemistry must be beneficial also to that branch of industry which is founded upon chemistry. It may be that in America the situation is different from what it is in Germany. Naturally I am insufficiently acquainted with the former, but I have been credibly informed during my stay here that in the industrial world the idea prevails that what can be done on a small scale in a laboratory experiment cannot 1 At the time this lecture was held, XNIETSCH'S concise description of the con- tract process for the manufacture of sulphuric acid had not yet been given. I refer the reader therefore to his exceedingly interesting communication. Her. d. deutsch. chem. GeselL, Vol. XXXIV, p. 4069 (cf. also SACKUB, ZeitschriftfiirElektrochemie^ol. VIII, p. 77). 45 46 PHYSICAL CHEMISTEY be accomplished on a large scale in the factory. Of course there is naturally a difference between laboratory experimen- tation and technical investigation. In the laboratory it makes no difference whether the process pays or not, while this is precisely the most important question in the works. Aside from this, however, one may state with confidence that what occurs in a test-tube can also be done with hundredweights of material, provided the conditions, for example of tempera- ture, are exactly imitated. The factory has, of course, resources so much beyond those of most laboratories that the imitation of laboratory conditions on a large scale is only a question of care. It is possible, however, that my informant did not reproduce the opinion in America on this point correctly. There exists in Germany a very beneficial co-operation between laboratory work and technical work. Both go as far as possible hand in hand. After physical chemistry had made several important advances and was firmly established in such a way that pure chemistry was assisted by co-operation with it, Ostwald judged correctly that this co-operation would also be valuable in technical directions. In this belief about eight years ago he founded the Electro- chemical Society, of which I happen at the present moment to have the honor of being president. I may add that in those eight years this society, whose chief object was to bring together the men of pure science and the representatives of technical science, has succeeded in gathering six hundred members. All the most conspicuous chemical industries of Germany and other countries are represented in the society. INDUSTRIAL CHEMISTRY 47 The society possesses in addition its own organ of publica- tion, the Zeitschrift fur Elektrochemie. At the last general meeting in Freiburg in Baden the desirability of expanding the society was discussed in order that the co-operation between technical and scientific chemistry might not be con- fined to the territory of electrochemistry. It seemed pos- sible to include physical chemistry as a whole, so far as parts of the subject other than this one had already found appli- cation or appeared to be capable of finding it. 1 Nor has the stimulus to this co-operation its source purely on the scientific side. That it comes from both parties may be seen, for example, in the fact that a year ago Professor Goldschmidt, at that time the representative of physical chemistry in Heidelberg, was asked by the directors of the Badische Anilin- and Sodafabrik to give a series of lectures on this branch of the science before the chemists of the factory, and did so with great success. That an opening up of new points of view in the treatment of practical problems was expected to flow from these lectures rather than immediate practical results, is evident when we consider the present purely empirical treatment of problems affecting industrial chemistry. Ultimately, however, direct results of its influence must appear without fail. In selecting for discussion industries in which the appli- cation of physical chemistry may be most useful, we turn naturally once more to the inorganic side. In this direction, as we have already remarked, physical chemistry is most i As the result of this discussion the society is now known as the "Deutsche Bunsen-Gesellschaft fur angewandte physikalische Chemie.' 1 [A. S.] 48 PHYSICAL CHEMISTRY easy to apply. In the first place I mention the treatment of the salts at Stassfurt, where the problem concerns the treat- ment of deposits which must be considered the results of the evaporation of sea- water. The substances concerned are the chlorides and sulphates of sodium, potassium, magnesium, and calcium. The study of these salts and of their solubility- relationships, recently resumed, and this time from the physico-chemical standpoint, may be expected to have some influence on their treatment for manufacturing purposes. In the second place we may name the field of metallurgy, par- ticularly alloys and steel. The study of these subjects in the same fashion, as has been stated by those with authority to speak on the subject, is likely to lead to a new epoch in siderology. The practical applications of electro-chemistry, which are being developed at Niagara, and in an especial degree also the use of so-called catalyzers, that is to say, substances which increase the speed of reaction of chemical changes, like platinum in the new method of making sul- phuric acid, likewise furnish an opportunity for the fruitful employment of physical chemistry. 1 A few examples will illustrate these possibilities. Let us begin with the salt industry and linger for a moment once more to continue the discussion of carnallite, which has the composition KC1 . MgCl 2 . 6H 2 O, and is well known to be one of the most important commercial sources of potassium compounds. The treatment of this double salt depends essentially upon 1 As the proofs of this work are being corrected I hear of the founding of an American Electrochemical Society, which according to the program of addresses has the object of assisting in such applications. INDUSTRIAL CHEMISTRY 49 the fact that, when the mineral is brought in contact with water, the magnesium chloride goes for the most part into solution, while the potassium chloride remains in the solid form. When the liquid has been saturated with carnallite the composition of the solution at 25 is expressed by the formula [1000H 2 O + 11KC1 + 73MgCl 2 ] .' The action of water in this case, therefore, corresponds with the equation: 73(KC1 . MgCl 2 . 6H 2 0) + 562H 2 O = [1000H 2 O + 11KC1 + 73MC1J + 62KC1 . When this saturated solution is concentrated, carnallite crystallizes out until finally chloride of magnesium begins to appear. At 25 this takes place when the composition of the solution has become [1000H 2 O + 2KCl + 105MgCl 2 ] . The result of this concentrating process, therefore, is expressed by the equation: [1000H 2 O + 11KC1 + 73MgCl a ]=339H 2 O+9.8(KCl. MgCl 2 . 6H 2 O) + . 6[1000H 2 O + 2KC1 + 105MgCl 2 ] . The final liquid is thus essentially a solution of magnesium chloride. The carnallite which has crystallized out can be treated with water as before. The disposition of the mag- nesium chloride mother-liquor, so as to avoid the contamina- tion of river waters, appears to be a problem of no little difficulty. i In what follows, symbols representing the composition of solutions are placed within square brackets. 50 PHYSICAL CHEMISTRY The re-examination of the carnallite problem from the physico-chemical standpoint, which we have discussed in the previous lecture, possesses the advantage that it shows at one glance all the possible methods of splitting carnallite. The one just referred to takes its place as a special case. As a result of this more general treatment, however, two other processes emerge and are to be considered as possi- bilities, even in the matter of technical application. One of these is founded on a transformation of carnallite in which, below 21, it takes up water and forms potassium chloride and the dodecahydrate of magnesium chloride. Working under these conditions the reproduction of about 14 per cent, of the original carnallite which occurs in the process at present in use would be avoided. After satura- tion with carnallite and separation of potassium chloride, a solution would be formed of the composition [1000H 2 O + 10KC1 + 66MgCl 2 ] . From this, by concentrating or cooling, magnesium chlo- ride with twelve molecules of water of crystallization and potassium chloride would be deposited. A second possibil- ity of obtaining potassium chloride is indicated by the decomposition of carnallite at 168. In this case three- quarters of the potassium chloride is separated, and one- quarter, with all the magnesium chloride and water, may be poured off in fluid form. The operation must of course be conducted in closed vessels, since the pressure of the water of crystallization in carnallite at 168 is greater than one atmosphere. If this liquid is separated from the INDUSTRIAL CHEMISTRY 51 solid potassium chloride by some sort of filter press, and is lowered in temperature to 115, the potassium chloride still contained in it reappears in the form of carnallite. The hot solution now remaining can again be separated from the solid by pressure, and is an almost pure, melted hydrate of magnesium chloride, free from potassium compounds. In the technical point of view a good deal may be said in favor of the last process. A decomposition of the carnallite (without the formation of any mother-liquor) takes place, in the course of which three-fourths of the potassium chloride as such and, in the final step, a corresponding amount of solid magnesium chloride are obtained, while a quarter of the car- nallite is recovered unchanged and can be worked up afresh. Thus, what in the ordinary process is attained by the use of a solvent and by taking advantage of solubilities is here reached by changes in temperature and the accompanying phenomena of transition or of melting and solidification. How far, however, a remunerative process is involved in this can be shown by future study only. So much we know, that the operation as it may be carried out in the laboratory with a few grams has also been found to work in the factory when several kilograms are used. The applicability of the method on a large scale is thus assured, as we might have expected. The question of cost alone remains open. As a second example, I desire to discuss the applica- tion of physical chemistry in the field of metallurgy. By far the most important illustration in this direction is in connection with the manufacture of steel and the explanation of its peculiarities. Authorities in this subject admit on all 52 PHYSICAL CHEMISTRY hands that physical chemistry has thrown a most welcome light on the complicated phenomena presented by the behavior of steel. These of course primarily depend upon the interactions of iron and carbon. The interactions, how- ever, are complicated by the fact that transformations occur both in the iron and in those constituents which contain both carbon and iron. It will simplify the matter greatly, there- fore, if we first consider the changes which occur in a single metal. We may take tin as being the metal in connection with which changes of this kind have been most com- pletely investigated. The remarkable fact in the behavior of tin to which I ask your attention was discovered long ago. Careful his- torical investigation has demonstrated that even Aristotle was acquainted with the fact, whose explanation has so recently been brought to light. The fact referred to is that common tin is capable of undergoing a profound change which amounts to a complete disguise. The product of this change, for reasons which we shall learn later, cannot be exhibited to you, and I must therefore content myself by showing a photograph of a piece of tin which is under- going this transformation (Fig. 4). The impression which examination of this piece of tin makes is that of an object which has been overtaken by some disease. As a matter of fact, indeed, the phenomenon has this in common with dis- ease, that it is contagious. When the phenomenon exhibits itself, as it sometimes does, in the pipes of church organs, it is consequently a good plan to remove the objects which have become infected. The disintegration into a gray or THE UNIVERSITY OF INDUSTRIAL CHEMISTRY 53 powder, which marks the progress of the attack, proceeds gradually until, especially in the case of thin bodies like organ pipes, the object has been completely destroyed. We must not delay to add that, in spite of appearances, the change is not due to the influence of the atmosphere or its moisture. On the contrary, the tin undergoes the change all by itself, and the gray product has only to be heated in order that without change of weight it may be reobtained in the original metallic form. It is precisely on account of the influence of heat on the change that, at the temperature which we are at present experiencing, I am unable to show this so-called gray tin. We owe particularly to Schaum l and Cohen 2 our knowl- edge of the conditions which influence this extraordinary change. The conclusion is that the whole phenomenon is related to a definite temperature, namely 20 C. Below this tem- perature the formation of gray tin can occur, while only above this temperature is the formation of the common variety possible. The temperature limit 20, commonly known as the transition point, separates two ranges of temperature in which the gray and the white tin respectively are stable. It exhibits thus a certain analogy to a melting-point, with this sole difference that at a melting-point a so-called change of state occurs. In the latter case the bodies are solid and liquid respectively. The temperature 0, for instance, can be named the transition point of ice and water. Along with this analogy between the two kinds of phenomena, which by l Liebig's Annalen, Vol. CCCVIII, p. 29. iZeitschr.f. physik. Chem., Vol. XXX, pp. 601, 623. 54 PHYSICAL CHEMISTRY the way were compared even by Aristotle, one striking differ- ence is to be noticed. This difference probably accounts for the fact that the limiting temperature of 20, which sepa- rates gray from white tin, was not discovered until the new methods of physical chemistry became available. This nota- ble difference lies in the extreme slowness of the change in the case of tin. Indeed, the change may fail to put in an appearance for years. In the case of ice and water, on the other hand, superheating of ice even for a moment seems to be impossible, and although overcooling of water beyond can occur, the slightest touch with ice destroys the overcooling instantly, and causes freezing. In the case of tin almost every possible means must be used to bring the change about, at all events when the temperature of experi- ment is not too far removed from 20. If this reluctance to change did not exist, the tempera- ture of transformation could be observed like a melting-point. It could be followed with the assistance of a thermometer, for, in close analogy to the* phenomenon of melting, the for- mation of white from gray tin is accompanied by the disap- pearance of heat. The extreme slowness of the process, however, renders the employment of other means necessary. I shall describe two of them. Before doing so, however, I should remark that delayed processes of this kind are in general more common in connection with chemical trans- formations than in physical changes of state, even though the latter are often closely analogous to the former. One of the methods makes use of the very notable change in volume which accompanies the transformation of the tin. INDUSTRIAL CHEMISTRY 55 Ordinary tin has a specific weight of 7.3, while in the case of gray tin this constant has the value 5.8. Thus, white tin expands more than a quarter in undergoing the change. An alteration in volume like this can be very easily studied by the help of a dilatometer. This instrument is a kind of thermometer of rather large dimensions. Its reservoir is packed with the substance under investigation in this case the tin. After the reservoir, which originally was open for the reception of the contents, has been closed, the air is pumped out, and a suitable liquid is admit- ted. The changes in the level of this liquid in the capillary tube serve as an indication of the alterations in volume which occur in the contents of the reservoir, and can be read off with the help of a scale. Without special precautions, however, the object could not be attained by these means alone, since, without stimulus, the transfor- mation often fails altogether to occur. The chief among the necessary conditions is that both kinds of tin inti- mately mixed should be introduced into the instrument. This intimate contact serves to stimulate either transfor- mation, so that the sensitiveness of the arrangement is great- est when equal quantities of the two bodies are present. An additional expedient is indispensable in the present case. The liquid used for filling the apparatus must be capable of dissolving to the greatest possible extent the body which is undergoing the change. A solution of pink-salt (SnCl 4 . 2NH 4 C1) has been found most suitable. The tin dissolves in this substance with the formation of stannous chloride. That one of the two transformations which under the given 56 PHYSICAL CHEMISTRY conditions tends to occur, is brought about through media* tion of this process of solution. One modification dissolves and the other is deposited. Working in this fashion the dilatometer, when kept at a constant temperature, shows the transformation in one direction or the other in admir- able, if somewhat leisurely, fashion. For example, a gradual increase in volume, which may continue for days, is observed at 19. On the other hand, a slow contraction occurs at 21. At 20 the system remains at rest, and thus the transition temperature is determined within one degree. While applications of the method the description of which we have just concluded always occupies several days or even weeks, a second plan, which is now to be mentioned, has the great advantage that the determination of the transition temperature can be made in a short time and with much greater accuracy. The second method makes use of the electrical currents which under suitable circumstances are produced by the transformations of the two forms of tin. The apparatus itself is again very simple. It consists of two short, rather thick-walled test-tubes, which are connected by a siphon or a cross-piece opening into the side of each. In one of the tubes some gray tin is placed, and in the other some white tin. Metallic contact with the material is made by means of two platinum wires fused into the bottoms of the test-tubes. These form the poles of a cell and are con- nected with a very delicate galvanometer. The circuit is closed by means of pink-salt solution, with which the two test-tubes and the siphon or cross-piece are filled. When the temperature is not far from 20 a direct transformation of INDUSTRIAL CHEMISTRY 57 the specimens of tin does not occur. The only consequence of the tendency to change is that on the one side the modi- fication which is unstable at the existing temperature passes into solution, while the metal in the other test-tube increases by deposition. Since, however, this deposition can occur only with the assistance of the positive ions of tin, the mass of tin which is increasing in quantity acquires a positive charge, while the other, which is furnishing positive ions to the solution, is losing an equivalent charge. The current which is produced in this fashion, and whose existence and direction may be foretold, can actually be observed. In con- sequence of the delicacy of electrical measurements, it fur- nishes a very exact indication of the direction in which the transformation is proceeding. The formation of the gray tin produces a current in one direction, that of the white in the opposite direction. The transition temperature is indicated by a reversal of the poles. LECTURE V PHYSICAL CHEMISTRY AND INDUSTRIAL CHEMISTRY Results of the Physico-Chemical Study of Wrought Iron, Cast Iron, and Steel Complications Introduced by the Presence of Carbon and by the Occurrence of Solid Solutions Method of Studying Iron by Polishing, Etching, and the Use of the Microscope Constitu- ents are Ferrite, or Pure Iron; Martensite, or the Solid Solution of Carbon in Iron; Cementite, or the Carbide of Iron; Graphite, or Free Carbon; Pearlite, or the Cryohydratic Mass Two Forms of Ferrite with Transition Point at 850 Pearlite, a Mixture of Cementite and Ferrite, and its Formation and Composition Hard Steel is Overcooled Martensite The Graphite The Be- havior of Melted Iron Rich in Carbon Rapid Cooling Gives White Cast Iron Containing Much Cementite Slow Cooling Gives Gray Cast Iron by Decomposition of the Cementite and Production of Graphite, and Finally Pearlite A Numerical Illustration of the Behavior of Molten Iron Containing 6% per Cent, of Carbon When Cooled (1) Rapidly and (2) Slowly. I SHOULD like to employ the second hour which is to be devoted to the application of physical chemistry to techni- cal chemistry, in giving you some conception of what it has done for the study of iron. Under this term we include not only wrought iron, but also cast iron and steel, which are forms of iron containing more or less carbon. I would call your attention first to the fact that von Juptner, one of the most noted authorities on steel, has described the results of this study as establishing an epoch in the iron industry. In recognition of this, his recent work on siderology is furnished with an introduction of sixty -one pages dealing with the laws .of solution. 58 INDUSTRIAL CHEMISTRY 59 The behavior of steel in particular is far from simple, and so yesterday I prepared for the introduction of this subject by explaining the simpler but somewhat analogous behavior of tin. Tin, like iron, is a metal, but, while in the case of the former we have a single substance occurring in different modifications, when we approach the study of the forms of the latter which are of technical importance, we find that the carbon which is present plays a very important part. In spite of this complication, the new physico-chemical method of treating such problems has illuminated successfully a rather confusing set of phenomena. It has made it possible to represent the whole behavior of carboniferous iron by means of one diagram, inspection of which enables us to grasp the essential features at one glance. A second introductory explanation is necessary. In the case of tin, the peculiar occurrence of a metal in different forms and the laws governing the transformation of these were emphasized. In the case of iron in its different condi- tions this phenomenon recurs, but a second, consisting in the appearance of so-called solid solutions, has also to be noticed. The grasp which we have obtained of the nature of ordi- nary fluid solutions has been so fruitful and its influence so far-reaching that the attempt has been made to proceed one step farther and to apply the same conceptions to substances in the solid condition. We are certainly entitled to speak of solid solution in certain definite cases, where the complete homogeneity combined with the possibility of varying com- position, which are characteristic of the state of solution, are found. In colored specimens of glass and in isomorphous 60 PHYSICAL CHEMISTRY mixtures, of two alums for example, we are just as little able, even with the help of the microscope, to perceive the presence of more than one substance, as in a solution of sugar in water. It is a familiar fact that the ordinary colorless alum, when crys- tallizing from solutions containing the highly colored chrom- alum, forms octahedra, more or less tinted with chrom-alum. And yet the most minute observation reveals no gross irre- gularities in the physical distribution of the material, or any other evidence of lack of homogeneity. In such a case, there- fore, we speak of the existence of a solid solution. When the substance is amorphous, as in the case of colored glass, the analogy to a fluid solution is so complete that the two are connected by a series of more or less viscous mixtures in such a way that no sharp distinction can be drawn. Of course, when the solid solution is crystalline it must be admitted that it differs from a fluid solution fundamentally, in so far that an arrangement of the molecules according to some definite order has taken place. The essential point is that the laws of fluid solutions have been successfully applied to solid ones, 1 and that this appli- cation has thrown light upon the behavior of varieties of iron containing carbon. Passing now from these preliminary statements in regard to tin and solid solutions, let us take up the main subject. The first thing to be noticed is that, while in the case of tin only two forms had to be considered, there are here more than two. In the industrial point of view there are three forms of iron wrought iron^ steel, and cast iron which tJber feste Lflsungen;" AHRENS, Sammlung chemisch-technischer For- tr&ge, 1900. INDUSTRIAL CHEMISTBY 61 differ from one another by containing proportions of carbon increasing in the order given. Obviously, too, the propor- tion of carbon is not the only thing to be considered. This is demonstrated by the change produced by chilling and hardening steel, which results from more or less rapid cool- ing following upon elevation to some definite temperature and occurs without any alteration in composition. On this account the investigation of iron demands not only analysis but also microscopic study. The specimen is first polished and then etched by the use of a solution of hydrogen chloride in alcohol. Sometimes continued polishing with emory and a plate of rubber is employed to secure a slight elevation of the harder parts above the more easily abraded, softer places. In either case, such a specimen, when studied microscopically so that the light falls upon it obliquely, shows peculiarities of structure which permit of further differentiation of the constituents. As a result of this we speak of ferrite, which is pure iron, of martensite, which is carboniferous iron of varying composition but homo- geneous structure (the solid solution), and of cementite, a compound of iron and carbon corresponding to the formula Fe 3 C. Besides these, pure carbon in the form of graphite, and sometimes of diamond, is discoverable. A fifth con- stituent is pearlite, a carboniferous iron, heterogeneous in structure, but possessing a constant composition. It may be that still other forms should be discriminated, but their exist- ence has not yet been determined with perfect certainty. 1 i BAKHUIS-ROOSEBOOM, Zeitschr. f. physik. Chemie, Vol. XXXTV, p. 437; BENEDICKS, ibid.. Vol. XL, p. 545 ; STANSFIELD, Journal of the Iron and Steel Insti- tute, 1900, Vol. II. 62 PHYSICAL CHEMISTRY Beginning with pure iron (ferrite), I mention first a fact determined by Le Chatelier. He found that, like tin, iron exists in two forms, whose transformation is dependent upon a definite temperature, which in this case is 850. These two forms we shall distinguish as a-ferrite and /3-ferrite. That which is stable in the cold, and in general below 850, is a-ferrite. Soft wrought-iron which has been freed as far as possible from carbon, as, for example, piano-wire, is of this kind. We record this first fact in the diagram, Fig. 5, in which the temperature is read along the axis of abscissae and the content of carbon along the axis of ordinates. The second fact which must be noted is that /3-iron is capable of taking up carbon in solid solution, while a-iron does not possess this property. Recalling the analogy between transition temperatures and melting-points, and the additional conception of solid and fluid solutions, we per- ceive that the addition of carbon to /8-iron will depress the temperature of transformation, just as dissolved substances lower the freezing-point of melted bodies. Yon Jiiptner has even applied the laws of fluid solutions to calculation of the extent of this depression. Graphically this depression is expressed by a line proceeding from the point 850 on the horizontal axis and ascending to the left in correspondence with the lowering in temperature and increasing content of carbon. Just as a melting-point cannot be depressed without limit by the addition of soluble substances, so is it with the transformation temperature of a solid solution like this. As the solvent gradually freezes out of a fluid solution, the INDUSTRIAL CHEMISTRY 63 proportion of the dissolved body in the mother liquor increases until finally the solute also comes out in some MMtfnjt Hoint< \ / 1 1 1 ' F / 6< : , per o<-nt. C 1000' , / (CaM Iron) * o '/ 2 / / 7 11:1 y , Vol. XXVII (1849), pp. 92, 172. 100 PHYSICAL CHEMISTRY and obtained as deposits calcium carbonate, sodium chloride, gypsum (CaSO 4 . 2H 2 O), magnesium sulphate with seven and with six molecules of water of crystallization, schonite (MgSO 4 . K 3 SO 4 . 6H 2 O), potassium chloride, carnallite, and magnesium chloride. Some very important constituents of the mineral deposits, and especially anhydrite, polyhalite and kieserite, which lend their names to three of the four regions, were lacking. We shall presently learn why experi- ments like those of Usiglio fail to correspond completely with the natural processes. It was necessary, therefore, to take up the problem by a different method and in a more gen- eral manner, and to secure an answer to the question, What is the influence, not only of the composition of the solution, but also of temperature, pressure, and time on the nature of the deposits which are formed ? We have only recently been able successfully to attack this question and to answer it. I must first give prominence to the fact that one fre- quently stated and indeed seemingly obvious principle is nevertheless not strictly correct. This principle is to the effect that the order in which deposits appear must correspond to the order of solubility in such a manner that the most sol- uble substance must come out last. It is certainly true that taken as a whole the order of the natural deposits is in har- mony with this, and that first a slightly soluble calcium salt appears in the form of anhydrite, then its combinations with more soluble sulphates, as polyhalite, then the easily soluble magnesium sulphate by itself as kieserite, and finally the very soluble carnallite. Yet it would obviously be quite possible to produce a solution so rich in magnesium sulphate GEOLOGY 101 and so poor in gypsum that when it was concentrated the more soluble magnesium sulphate would appear first. Thus the composition of the solution plays an important part in the order of the deposits. Then, too, while the solubility is also a determining factor, we have to remember that it may <: - vary very widely under the influence of other bodies which are simultaneously present. Let us first consider these two factors, the composition of the solution and the solubility of the substances present of it, and let us restrict the influence of temperature, pressure, and time by choosing a definite point, 25, for the first, atmos- pheric pressure for the second, and crystallization in the manner common in laboratories for the third. In this way we approach most closely the conditions of Usiglio's experi- ments, while considering the problem involved in the gradual removal of the solvent as a general one. The concentration of sea- water will thus arise as a special case, when in the course of this more general study the constituents of sea- water receive special consideration. Among the constituents, of course, the amount of sodium chloride occupies the place of chief importance. After it come the chlorides and sulphates of magnesium and potas- sium. Thirdly, there are the calcium salts, and with these, for our present purpose, the list closes. Now, in order to give a clear view of the composition of sea-water, let us express the proportion of the constituents, which, strange to say, if we exclude the calcium salts, is the same all over the earth, in molecules: lOONaCl-f- 2.2KC1 +7.8MgCl 2 +3.8MgSO 4 . 102 PHYSICAL CHEMISTRY Let us now develop the laws pertaining to the crystalliza- tion, step by step, taking the dissolved substances into account one by one. If a single salt is present the situation is very simple. As evaporation takes place the saturation point is finally reached and the salt in question separates out until the whole has dried up. So soon, however, as two salts are present, the ques- tion arises, Which will crystallize first, and when will the second appear? Let us answer this question, taking as the two salts potassium chloride and sodium FIG. 7 chloride at 25. We have only to remember that if, for example, the solution contains so much potassium chloride that this salt is the first to separate in the solid form, further concentration must gradually increase the content of sodium chloride until this substance also begins to appear. From this moment onward the solu- tion retains its composition unchanged. It simply dimin- ishes in volume and deposits both salts until the solvent is all gone. Obviously the same ultimate solution must be obtained if we start from the opposite side with a sufficient excess of chloride of sodium. The whole situation is thus clear when we know the composition of the final solution which is saturated with both salts. Analysis of a solution which has been agitated for a sufficient length of time with an excess of both salts at 25 gives the following result: GEOLOGY 103 [100H 2 O + 89NaCl + 39KC1] (C, Fig. 7). Thus, solutions which contain a greater ratio of sodium chloride to potassium chloride than 89 X 58.5 : 39 X 74.5 will first deposit sodium chloride. In the opposite case potassium chloride will first appear. Here, then, the relations are still of a simple character. In order that they may retain their comprehensibility when applied to more complicated cases, let us represent them graphically as in Fig. 7. To complete the figure, we require the solubility of sodium chloride, which is expressed by the formulae [1000H 2 OH-lllNaCl] (A, Fig. 7), and that of potassium chloride, which is [1000H 2 O + 88KC1] (B, Fig. 7). Now, with O as origin, let us lay off the amount of sodium chloride in the vertical direction and that of potassium chloride horizontally to the right. When this is done the data given above lead to three points, which we have desig- nated in order C, A, B, and if we now connect A and B with C the line AC represents saturation with sodium chloride, while the proportion of potassium chloride increases. Simi- larly, the line BC stands for saturation with potassium chloride, while the content of sodium chloride increases. It is now easy to see what must take place when any solution is concentrated. Let it be an unsaturated one, corresponding in composition to a point c inside the area OACB, its situation being given by the proportions of the respective chlorides. When evaporation begins, the relative 104 PHYSICAL CHEMISTRY proportions of the chlorides do not alter, but their quantity, calculated on the basis of the number of molecules in every 1000H 2 O, must increase. This change corresponds to a motion away from O along a straight line connecting O with c, that is to say, a motion along cd. When BC is encoun- tered at d, this means that separation of potassium chloride begins, and here a change in the direction of the motion occurs which reflects an ensuing phenomenon. The direc- tion taken is now towards C, or, in other words, is away from B in the direction of the arrow. When C is reached, sim- ultaneous separation of both salts begins, and this stage reaches its conclusion when the solution has dried up. This must ultimately occur to every solution after this point has been reached, and we therefore name C the final point of crystallization. We may now read in this graphic representation the law upon which ultimately, even in the most complicated cases, the progress of crystallization is founded. In words, it amounts to this, that in depositing its contents the solution gradually varies its composition away from that of a solution which is saturated with the substance being deposited at the moment and contains nothing but this substance. The prin- ciple becomes quite clear if we reverse the process which takes place during crystallization from an evaporating solution, i. e., if we add continually water and the salt which is being deposited. Under these circumstances obviously the solution tends to become more and more a saturated solution of this salt alone, since the other constituents, whatever they may be, must gradually become relatively negligible in quantity. GEOLOGY 105 In the graphic representation given in Fig. 7 we may perceive four applications of this law. If potassium chlo- ride separates on BC we move in the direction away from B, where saturation with potassium chloride is represented; if sodium chloride appears upon AB we move away from A, where saturation with sodium chloride exists. If both salts are deposited at C, we remain at rest at C, since we can move neither towards A nor towards B, and everything else is excluded. If nothing separates at c, we proceed in the direction away from O, where the solution contains nothing whatever. All this, which in the present case is obvious, will later furnish us with valuable guidance. Let us proceed then to the consideration of a more complicated case. Keeping the salts found in sea-water in view and .look- ing at the composition of sea-water, [lOONaCl + 2 . 2KC1 -f 7 . 8MgCl 2 + 3 . 8MgSO 4 ] , we could now add to the combination sodium chloride and potassium chloride, a third salt, e. g., magnesium chloride. We shall reach the goal more quickly, however, if we first consider the salts potassium chloride, magnesium chloride, and magnesium sulphate, and only at the very end take into consideration the chloride of sodium, which is always pres- ent in excess. Proceeding systematically we have first the combination potassium chloride and magnesium chloride, that is to say, a combination with a common acid, then that of magnesium chloride and magnesium sulphate with a common base. Further, however, if the problem is stated in a general form, potassium sulphate, which has not been mentioned, must be 106 PHYSICAL CHEMISTRY taken into account, since it may arise out of potassium chLpride and magnesium sulphate. The third combination is thus magnesium sulphate and potassium sulphate with a common acid, and the last will be potassium sulphate and potassium chloride with a common base. Let us now collect into one table the data in regard to solubility which are required as the basis of graphic representation for this cycle of substances. Three of them have just been given. For the present purpose, however, we now represent all the salts in equivalent amounts, so that potassium chloride is in double molecules. OATUKATION WITH K,C1 2 MgCl 2 MgS0 4 K 2 SO< A Potassium chloride 44 E. Potassium chloride and carnallite &A 1 72^ 105 .... .... B Magnesium chloride 108 G Magnesium chloride and MgSO 4 . 6H 2 O . 104 14 H MgSO 7H 2 O and MgSO 4 6H 3 O 73 15 C MgSO 4 .7H 2 O 55 J MgSO 4 7H 2 O and schonite. . . 58 U 5^ K Potassium sulphate and schonite 22 16 D Potassium sulphate. 12 Li Potassium sulphate and potassium chloride 42 VA IN MOLS. PER 1000 MOLS. H* The presentation of the whole of this material graphically makes the understanding of it much easier. The rectangular axes in the plane of the paper can be retained and from their point of intersection at O (Fig. 8) the four single salts, potassium chloride, magnesium chloride, magnesium sulphate, and potassium sulphate, can be laid off in the GEOLOGY 107 FIG. directions, A, B, C, and D, respectively. The four combina- tions which they form, two by two, fall then within the quadrants lying between the axes. We obtain in this way a fashion of representing the facts something like Fig. 7 108 PHYSICAL CHEMISTRY repeated four times. In this case, however, in three of the quadrants a complication arises from the existence of an inter- mediate compound. Between A, saturation with potassium chloride, and D, saturation with potassium sulphate, there is only the point L, where the solution is saturated with both. Between A and B, however, carnallite (KC1 . MgCl 2 . 6H 2 O) appears, and thus two determinations are necessary, which have been added at E and P and stand for saturation with carnallite and potassium chloride in the one case, and the same compound with magnesium chloride in the other. In the same fashion between B and C magnesium sulphate with six molecules of water crystallization appears in GrH and be- tween C and D the mineral schonite (K 2 Mg(SO 4 ) 2 -f6H 2 O) along JK. The progress of crystallization, using the same principle as before, is just as easy to follow, and is indicated by the arrows which in each quadrant are directed towards a so-called final point of crystallization. In this diagram these points are F, G, J, and L. So far, however, we have only considered a part of the possibilities, for solutions are entirely lacking which contain everything, that is to say, chlorine and sulphuric acid, potassium and magnesium. The experimental treatment of this question may best be shown by means of an example. Let us start from L (Fig. 8), where the solution at 25 is saturated with potassium chloride and potassium sulphate simultaneously. Taking care that both potassium salts are present in excess and in contact with the solution, we add magnesium in the form of chloride or sulphate. The solu- tion then takes up magnesium, but remains still saturated GEOLOGY 109 with potassium sulphate and potassium, chloride. Finally its capacity for taking up magnesium becomes exhausted, and a solid magnesium salt is deposited. This in the case before us is schonite (K 2 Mg(SO 4 ) 2 . 6H 2 O). After this, fur- ther addition of the magnesium salt will not lead to any being dissolved ; the consequence will simply be an increase in the amount of schonite. The solution will retain its constant composition, since it is and remains saturated with potassium sulphate and potassium chloride. We determine the com- position of this solution by analysis, using a mixture which at 25 after prolonged agitation is seen to be in contact with all the three salts and is found to have attained a constant composition. The result is represented by the following formula : [1000H 2 -f 25K 2 C1 2 + HMgS0 4 + 21MgCl 2 ] . Our task is thus finally limited to finding the solutions saturated with three salts and analyzing those solutions. Many such are a priori possible, if we consider the seven different compounds which have to be taken into account. The possible number would be: 7x6x5 1x2x3 -=35 . As a matter of fact, however, only a few of these possibili- ties are realized, and when a solution obtained in the above manner is systematically evaporated at 25, and the salt deposits are continually removed, the possibilities which are actually realized are found to be limited to four, in addition to the one described. 110 PHYSICAL CHEMISTRY After potassium chloride and schonite have come out, magnesium sulphate with seven molecules of water of crys- tallization appears as an additional salt. The deposit having been removed, this hydrate of magnesium sulphate and potassium chloride are now deposited until finally magne- sium sulphate with six molecules of water of crystallization is added to these two salts as a new constituent. From this point onward the hexahydrate of magnesium sulphate with potassium chloride crystallizes until carnallite makes its appearance. After this the hexahydrate of magnesium sul- phate with carnallite constitute the deposit until magnesium chloride appears, and now the solution dries up completely to a mixture of the three last-named substances. Collecting once more the quantitative measurements con- nected with these deposits, we have the following table: IN MOLS. PEE 1,000 MOLS. H 2 O SATURATION WITH K 2 Cl a MgCl a MgS0 4 M. Potassium chloride, potassium sulphate, schonite 25 21 11 N. Potassium chloride, MgSO 4 .7H,O, schonite P. Potassium chloride, MgSO 4 . 7H 2 O, MgSO 4 6H O 9 8 55 G2 16 15 Q. Potassium chloride, carnallite, MgSO 4 6H 8 O 4M 70 13^ R. Magnesium chloride, carnallite, MgSO 4 6H 8 O 2 99 12 The next thing is to represent these numbers graphically, and when this has been done we are presented with a complete view of the whole process of crystallization. GEOLOGY 111 To do this a third dimension is obviously required. We add a third axis passing through O, vertical to the former system of axes (Fig. 8), and along this we lay off the number of molecules. In practice this may be done conveniently by means of a model consisting of a piece of wood in which vertical needles are set at the proper places, with their lengths adjusted to the number of molecules. A horizontal projection on this model is shown in Fig. 9, whose border obviously coincides with the outline of Fig. 8, and whose points M, N, P, Q, and R represent the above data. 1 This having been done, each pair of points representing satura- tion with the same two salts for example, M and L, where in both cases saturation with the sulphate and chloride of potassium exists is connected by a line. These lines divide the figure into areas, each of which corresponds to saturation with a definite salt, as follows: EQPNMLA - Potassium chloride EQRF - Carnallite FRGB - Magnesium chloride RGHPQ MgS0 4 .6H 2 PHCJN - MgSO 4 .7H 2 O JKMN SchOnite KMLD - Potassium sulphate The progress of crystallization is given in each area by lines which proceed away from the points which represent saturation with the body itself, as a single constituent. Thus, in the potassium chloride area, these lines proceed from A in all directions. i It may be remarked that this method of presenting the facts is not influenced by the condition in which one supposes the salts to be present in the solution ; that is to say, whether they are K 2 C1, and MgSO 4 or MgCl, and K,SO 4 . 112 PHYSICAL CHEMISTRY D FIG. 9 Let us apply this now to a particular case, taking, for example, a solution containing a gram-molecule of magne- sium chloride and a gram-molecule of potassium sulphate. The preliminary evaporation without any deposit appearing GEOLOGY 113 corresponds to motion from the origin in the vertical direc- tion until the area lying immediately above it that is to say, the potassium sulphate area is encountered. Potas- sium sulphate should separate out, and this, as a matter of fact, is just what occurs. We next expect a movement away from D until the limit KM is reached, where schonite should appear, and this expectation is also fulfilled in practice. If the salts as they come out are always removed, the deposition of schonite corresponding to a movement across the schonite area in the direction of the lines drawn upon it takes place until MN is reached, indicat- ing the beginning of potassium chloride crystallization. This salt does actually appear next. Here the course of the paths of crystallization from both sides shows that with fur- ther concentration we remain 1 on the line MN until at N magnesium sulphate begins to be deposited. The rest of the changes may be read from the diagram in the same manner. Not only can we thus follow the progress of the crystallization, qualitatively, however. We can calculate the quantity of each substance which will be separated when a given point corresponding to a known composition is reached. The results agree exactly with experiments which have been made in a variety of ways. Thus Fig. 9 contains the basis for understanding and even predicting the whole process of crystallization. When a beginning has been made in applying the prin- ciples according to which crystallization proceeds, the addi- i For this reason boundaries like MN are named bases of crystallization. There are four of these proceeding from the final points of crystallization, L, J, G, and F. All meet together at the common final point B. 114 PHYSICAL CHEMISTRY tional compounds occurring in the natural deposits can easily be introduced into the scheme. These are sodium chloride and the salts of calcium. We shall not attempt to carry out this extension in detail. It may simply be mentioned that a scheme corre- sponding to Fig. 9 can be, and has been, laid out for the case in which all the solutions are saturated with sodium chloride at 25, a state which corresponds with natural conditions. So far as the salts of calcium are concerned, their solubility is so small that they do not seriously alter the composition of the solutions themselves. It is only necessary to de- termine from which of the solutions calcium in the form of gypsum (CaSO 4 .2H 8 O), anhydrite (CaSO 4 ), syngenite (CaSO 4 .K 8 SO 4 .H 8 O), or some other form, will be de- posited. LECTURE IX PHYSICAL CHEMISTRY AND GEOLOGY The Influence of Time and of Variations in Temperature and Pressure on Deposition The Time Factor and Delayed Crystallization Several Compounds, Found in Nature, Do Not Appear at All in Laboratory Experiments on Deposition, but Can Be Included in the Scheme by the New Method of Agitation with Solutions The Behavior at Temperatures above 25 New Minerals Formed above 25 and Absent at 25 New Combinations of Minerals Possible above 25 Disappearance above 25 of Minerals Formed at that Temperature The Influence of Possible Changes in Pressure Too Slight to Affect the Results. THAT to which in this second lecture on geology I should like chiefly to devote my attention is the consideration of the parts which time, temperature, and pressure play in modify- ing the nature or amount of the deposits. Their impor- tance diminishes in the order stated. Time is the most important factor, and yet its influence is the most difficult of the three to determine by laboratory experiments. In direct experiments on the crystallization of sea-water, such as were made by Usiglio, obviously time received less consideration than anything else, and a better approach to a knowledge of the geological processes is hardly possible by his method, in consequence of the speed of the experiments. The method of treating the subject described here is more favorable in this respect. At first it is true the results accord essentially with those of Usiglio. In the course of further investigation, however, one com- 115 116 PHYSICAL CHEMISTRY pound after another is obtained which, on account of retardation of quite unexpected extent, is entirely missed when the ordinary method of crystallization is employed. Such retardations are known to you in the case of so-called supersaturated solutions, such as that of Glauber's salt. Supersaturations of this kind, however, are easy to avoid by introduction of the substance, here Glauber's salt, in respect to which supersaturation exists. In imitation of this we have always prepared our saturated solutions by long agita- tion with the salts in respect to which saturation is required. After this has been done, a filtered sample is brought in contact with well-developed crystals of the same salts, in order that the question of the existence of satura- tion may be definitely settled. This procedure had seemed to make success only a question of hours, or at most of days, until we unexpectedly found that some compounds whose formation in the solutions under investigation was pos- sible at 25, nevertheless totally failed to put in an appear- ance. These, not to mention the salts of calcium, were leonite,K 3 Mg(SOJ 2 .4H 2 O; kainite, MgSO 4 . KC1.3H 2 O; and kieserite, MgSO 4 .H 2 O. Even exceedingly slow crys- tallization with the addition of the compounds themselves did not remove the condition of supersaturation in the case of these bodies. Precisely in this region the new method of treatment shows its superiority, since it is not dependent upon direct crystallizations. It relies on the determination of solubility data, and relatively few of these, to give a complete view of the whole plan of crystallization, both qualitatively and GEOLOGY 117 quantitatively. Now, data of this kind, in the case of the bodies just mentioned, may be obtained in spite of the tendency to retardation, although agitation may sometimes have to be continued for weeks. Let us now present the data obtained from such experi- ments : SATURATION WITH SODIUM CHLORIDE AND Na,Cl, K,C1, MgCl, MgS0 4 Na 7 S0 4 o 551^ A MgCl a 6H a O 2U 103 B KC1 44^ 19i/ C. Na 2 SO 4 . . 51 12^ D MgCl a 6H 2 O, carnallite 1 U 103^ E. KC1, carnallite 2 &A 70^ F. KC1, glaserite 44 20 4^ G. Na 2 SO 4 , glaserite 44^ IOK 14^ H. Na 8 SO 4 , astrakanite 46 iw 3 I MgSO 4 .7H a O, astrakanite . 26 7 34 J. MgSO 4 .7H 2 O,MgSO 4 .6H 2 O.... K. MgSO 4 . 6H 2 O, kieserite 4 2^ .... 67^ 79 12 9^ .... L Kieserite MgCl 2 .6H 2 O 1 102 5 M. KOI, glaserite, schdnite 23 14 21 y 14 N. KC1, schonite, leonite 14 11 37 14^ P. KC1, leonite, kainite . 9 9^ 47 14^ Q. KC1, kainite, carnallite 2^ 6 68 5 R. Carnallite, kainite, kieserite S. Na 2 SO 4 , glaserite, astrakanite . . . T. Glaserite, astrakanite, schonite . . U. Leonite, astrakanite, schonite V. Leonite, astrakanite, MgSO 4 . 7H 2 O y z 42 27^ 22 1(W 1 8 IOK 10K 7^ 85^ 16K 23 42 8 16 18& 19 19 6 W. Leonite, kainite, MgSO 4 . 7H,O . . X. MgSO 4 .6H 2 O, kainite, MgSO 4 .7H 8 O 9 3*4 ty* 4 45 65^ 19^ 13 Y. MgSO 4 ,6H 2 O, kainite, kieserite . Z. Carnallite, MgCl,. 6H 2 O, kieserite VA 2 H 77 100 10 5 .... MOLS. WITH 1000 MOLS. H,O 118 PHYSICAL CHEMISTRY Those data may be represented by a model, in the way previously described. A projection of this model is shown in Fig. 10. The basal plane is in so far different that the sodium chloride is not represented in the model, while the sodium sulphate is not taken into account in the number of molecules, in consequence of the relation Na 2 SO 4 = Na 2 Cl 2 + MgSO 4 - MgCl 2 The latter is measured off upon an axis OC, which bisects the angle DOB. The areas correspond to the following substances : Area Formula Mineralogical Name 1. ALZD MgCl 2 .6HoO Bischofite 2 BFMNPQE KC1 Sylvite 3 CGSH Na 2 SO 4 Thenardite 4. DZRQE KMgCl 3 .6H 2 O Carnallite 5. FMTSG 6. SHIVUT 7. JXWVI K 3 Na(S0 4 ) 2 Na 2 Mg(S0 4 ) 2 . 4H 3 MgSO 4 .7H 2 O Glaserite Astrakanite Reichardtite 8 JXYK MgSO 4 .6H 2 O (Not found) 9. KYRZL 10 TUNM MgSO 4 .H 3 O K 9 Me(S(X), 6H 9 O Kieserite Schonite 11 NUVWP KoMg(SO,)o, 4H a O Leonite 12 PWXYRQ MgSO 4 .KC1.3H^O Kainite and the progress of crystallization may be developed on the same principle as before. The next thing to be considered is the influence of tem- perature. Solubility is, as we all know, very generally influ- enced by change of temperature, and such a change will therefore alter a diagram constructed for 25. For our pur- pose it is important to determine what geological information GEOLOGY 119 120 PHYSICAL CHEMISTRY may be obtained in this direction. The most significant thing is the appearance of additional minerals which cannot be formed as low as 25. Then follows the appearance of additional combinations of minerals. Finally the disappear- ance of some minerals is to be noted. Among the appearances of minerals at temperatures above 25 two may be mentioned by way of illustration. Among the chlorides and sulphates of potassium, magnesium, and sodium, two known materials are absent at 25, namely langbeinite, K 2 Mg 2 (SO 4 ) 3 , and loeweite, Na 2 Mg(SO 4 ) 2 . 2H 2 O. The failure of these substances to appear is not a consequence of retardation, for in the solutions in which at 25 they would first be formed, they are actually decomposed by interaction with water. Thus langbeinite becomes a mix- ture of magnesium sulphate and leonite according to the equation : K 2 Mg 2 (SO 4 ) 3 + 11H 2 O = MgSO 4 . 7H 2 O + K 2 Mg(S0 4 ) 2 . 4H 2 and loeweite gives astrakanite: Na 2 Mg(SO T ) 2 . 2H 2 O + 2H 2 O = Na 2 Mg(SO 4 ) 2 . 4H 2 O . This fact furnishes us with a hint in the determination of the temperature at which these bodies would be formed. The products of their hydration have only to be heated in con- tact with that solution which is saturated with them, and possesses the greatest water- withdrawing power. In the case of langbeinite this is the solution W (Fig. 10), where the necessary saturation with magnesium sulphate and leonite exists, and where, besides, kainite, with which the solution GEOLOGY 121 is simultaneously saturated, contributes to the water-remov- ing power. In contact with this, langbeinite is formed from its products of hydration above 37, while below this tem- perature the change is reversed. The occurrence of lang- beinite in the natural salt deposits thus indicates the existence of a temperature above 37. A similar temperature limit of 43 is found for loeweite. Let us now turn to the second influence of temperature, that, namely, on the simultaneous occurrence of minerals. This is shown in Fig. 10 for the temperature 25. We shall present the same figure in a simplified form, preserving all the lines of contact, but changing shapes of the areas to rectangles. We then see that glaserite, for example, can occur along with astrakanite, but not along with bischofite. This figure (Fig. 11) contains material for a great number of geological inferences. When I was exhibiting Fig. 11 in a lecture on this subject in Strassfurt, Dr. Schwab directed my attention to "hartsalz," a mixture of kieserite and potassium chloride, which is excluded at 25, since the two areas are separated by kainite. This problem was taken up by Meyerhoffer, who found that "hartsalz" is a product peculiar to a much higher tempera- ture, somewhere in the neighborhood of 70. This tempera- ture is probably the highest of which we have any indication in connection with this subject. The third point, the disappearance of some minerals, might also be employed as a geological thermometer. Thus, the existence of reichardtite, MgSO 4 . 7H 2 O, is determined by an upper limit of 47, that of schonite by the temperature 122 PHYSICAL CHEMISTRY Finally the pressure must be considered. It has often been hinted at as a possible agency in the formation of minerals, which, like anhydrite, fail to appear in laboratory A L K J I H C Bischofite MgCl 2 . 6H 2 O I) E B z Kieserite Carnallite MgSO 4 . H 2 O KMgCl 3 . 6H,O Y MgS0 4 .6H 2 R Kainite MgSO 4 .KC1.3H s O Q p Sylvite KC1 N M X Reichardtite MgSO 4 . 7H 2 O Leonite K 2 Mg(S0 4 ) 2 .4H 2 V U Astrakanite Na 2 MgiSO 4 ) 2 .4H 2 O T S Schonite K 3 Mg(S0 4 ) 2 .6H 8 Glaserite K 3 Na(S0 4 ) 2 Thenardite Na 2 S0 4 G F FIG. 11 experiments, when the cause of this was simply retardation. On reflection we find that the influence of pressure in the formation of natural salts must be relatively small. In the case of the Strassfurt deposits, for instance, we cannot count upon a greater depth of sea-water than 1500 meters. GEOLOGY 123 Assuming the specific weight, when the deposition of salts begins, to be 1.2, this would indicate a pressure of 1500 X 1.2 - 10 atmospheres Now, the chief effect of the pressure is that temperatures of formation, such as the 37 in the case of langbeinite, are displaced. They are raised when, as is commonly the case with actions involving the separation of water, a simultaneous expansion takes place. The extent of these displacements is, however, of the same order as that which the melting-points show under the influence of the same agency. It may be determined theo- retically. We have measured it experimentally also in con- nection with the formation of the mineral tachhydrite, Ca(MgCl 3 ) 2 . 12H 2 O, with the anticipated result. It was found that a single atmosphere of pressure only affected the temperature, here 22, by a few thousandths of a degree. The actual measurement was 0.017, which for 180 atmospheres would correspond to 3. Since in the case of the formation of salt deposits, according to the latest direct observations with the salt mother-liquors of Siebenburgen by Kaleczinsky, 1 changes in temperature of 50 have to be reckoned with, the considera- tion of pressure is very much less important in the study of this problem than is that of temperature. 1 Uber die ungarischen warmen und heissen Kochsalzseen, Budapest, 1901. INDEX ACETIC ACID, 87. ALCOHOL, 87. AMYGDALIN, 84, 92. ANHYDRITE, 99, 100, ARRHENIUS, 24, 39. ASTBAKANITE, 118. AVOGADKO'S LAW, 17; applied to solu- tions, 19, 73. BAKER, 91. BAKHUIS-ROOZEBOOM, 25, 67. BECKMANN, 81. BENZALDEHYDE, 84, 92. BERTHELOT, 17, 31, 33, 87. BISCHOFITE, 118. CALCIUM CARBONATE, 100. CARNALLITE, 99, 100; graphic represent- ation of its region of stability, 29 ; illus- trating the new and comprehensive method of studying a problem, 25; method of manufacturing potassium chloride from, 48; three methods of splitting up, 50; transition point at 21% 27, 34 ; transition point at 168", 28. CARNOT-CLAUSIUS PRINCIPLE, 20. CAST IRON, white and gray, 67. CATALYTIC ACTION, 85. CEMENTITE, 61. COHEN, 53, 75. CONSERVATION OP ENERGY, 20. CRYSTALLIZATION: final point of, 104; graphic representation of, 102, 107, 112, 119, 122. DANIELL CELL, 36. DEPOSITION: influence of pressure on, 122; influence of temperature on, 118; influence of time on, 115. DB VRIES, 74. DILATOMETER; use of, in determining transition point of tin, 55. BONDERS, 77. DUHEM, 6 ELECTRICAL METHOD: of determining transition points, 56; of measuring affinity, 36. ELECTROLYTIC DISSOCIATION, 39. EMMEBLING, 92. EMULSIN, 84,92. ENZYMES, 84, 90. EQUILIBBIUM, CHEMICAL, 37, 86. EYCKMAN, 81. FEBTILIZATION, ABTIFICIAL, 80. FERRITE, 61. FORMULA, STRUCTURAL, 4. GLASERITE, 118. GLUCOSE, 84, 86, 92. GOLDSCHMIDT, 47. GRAPHITE, 61, 66. GYPSUM, 100. HAMBURGER, 77. HARTSALZ, 121. HILL, 92. HYDROCYANIC ACID. 84, 92. IONIZATION : and physiology, 82 ; theory of, 38. IRON: transition point at 850% 62. KAINITE, 99. KALECZINSKY, 123. KEKUL, 4. KIESERITE. 99, 100. KOEPPE, 79. KOHLRAUSCH, 41. LADENBURG, 3, 6. LANGBEINITE, 120, 121. LEMOINE, 91. LEONITE, 118. LOEB, 10, 74, 80. LOEWEITE, 120, 121. MAGNESIUM CHLORIDE, 100, 105. MAGNESIUM SULPHATE, 100, 105. MALTASE, 93. 125 126 PHYSICAL CHEMISTRY MALTOSE, 92. MAETENSITE, 61. MASSAET, 78. MAXIMUM WOBK : principle of, 31, 32, 35. MEYEBHOFFEB, 25, 97, 121. NEENST, 24, 41. OPTICALLY ACTIVE SUBSTANCES, 89. OSTWALD, 23, 41. OSMOTIC PBESSUEE, 7, 74, 76 ; in bacteria, 79; in blood corpuscles, 77; in plants, 76; in the eye, 78; measurement of, 81. PAN DE ST. GILLES, 87. PEAELITE, 61, 64. PFEFFEB, 7. PHOSPHONIUM CHLOBIDE, 33. PHYSICAL CHEMISTEY : industrial appli- cations of, 48 ; introduces new concep- tions, 17 ; is not merely the use of phy- sical instruments, 16; its founders, 23; its place in the science, 6 ; its three modes of application in inorganic chemistry, 24; what it has accom- plished, 6; why applied chiefly in in- organic chemistry, 24. PHYSIOLOGICAL CHEMISTBY, 9, 41. PLAN OF THE LECTUEES, 15. POLYHALITE, 99, 100. POTASSIUM CHLOBIDE, 99, 100, 102, 105; three methods of obtaining it from carnallite, 48, 50. POTASSIUM SULPHATE, 105. PBEDICTION OF BEACTIONS, 31, 33. EAOULT, 40, 81. REICHABDTITE, 118. REVERSIBLE CYCLES, 21. EEVEBSIBLE CHEMICAL ACTIONS, 87. SALT DEPOSITS : stratification of, 99. SALTS: deposition of three, 106; depo- sition of two, 102. SCHAUM, 53. SCHONITE, 100, 109. SCHWAB, 121. SEA WATEB, 98, 101. SODIUM CHLOEIDE, 98, 100, 102. SOLUTIONS, SOLID, 59. STEEL, 58; explanation of hardness of, 66; graphic representation of behavior of, 63; methods of examining structure of, 61 ; tempering of, 61. STEEEOCHEMISTEY, 5. SYLVITE, 99, 100, 102, 105. SYNGENITE, 114. TACHYDEITE, 123. TAETAEIC ACID, 89. TEMPEBING OF STEEL, 61. THALLIUM SULPHOCYANATE, 37 THENAEDITE, 118. THEEMODYNAMICS, 20. THOMSON, 17, 31. TIN DISEASE, 52. TIN: gray, 52; specific weights of white and gray, 55 ; transition point of, 54. TBANSITION TEMPEEATUEES, in alchemic change, 25. TEYPSIN, 92. USIGLIO, 99. VON JUPTNEB, 58, 62. WlNKLEE, 6. WOBK : possibility of accomplishing, as measure of chemical affinity, 33, 36. YEAST, 84, 92. ZYMASE, 85. UNIVERSITY OF CALIFORNIA LIBRARY BERKELEY Return to desk from which borrowed. This book is DUE on the last date stamped below. IBRA*Y REC'D LD MAR 19 '65-3 PM DEC 1 4 2003 MAR 2 2 2004 Mayi'SOE LOAK LD 21-100m-9,'48(B399sl6)476 YC THE UNIVERSITY OF CALIFORNIA LIBRARY y Q^9 O