The BEGINNING ofLIQUID AMMONIA RESEARCH in the UNITED STATES* ROBERT TAFT The University of Kansas, Lawrence. Kansas
HE properties of liquid ammonia as a solvent and the ammonia systems of compounds are now quite familiar to the chemists of the present day. On the other hand, the events leading up to the initiation of the experimental work in this country, upon which most of our knowledge of this subject is based, are not so well known. The conditions under which ideas are formed, put into execution, and developed into a well-defined branch of science are usually of interest and never without instructive value. For
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* This paper has been read and approved by Dr. Franklin, Dr. Kraus, and Dr. Cady.
this reason, as well as to make the historical record while the principals in the events here recorded are still with us in the flesh, the present paper has been written. The principals just mentioned are three wellknown American chemists, Professors H. P. Cady, E. C. Franklin, and C. A. Kraus. As the work to be described was begun a t The University of Kansas in the middle nineties, a brief setting of the historic stage, with respect to both local conditions and the development of chemical theory, may enable the reader to obtain a truer perspective of the events to be noted.
By 1895 theoretical chemistry had been in existence as a well-recognized and separate branch of the science for relatively few years. Indeed, H. C. Jones, in his book "A New Era in Chemistry," dates the beginning of this era from the establishment by Ostwald, van't Hoff, and others, of the Zeitschrift fiir physikalische Chemie in 1887. 1895 would find us then in the eighth year of the new era. Few textbooks of physical chemistry were available, especially in this country. Nernst's "Theoretical Chemistry" had appeared, however, in an English translation in this year (1895). The books of Ostwald, which were to have such a marked influence on the development of physical chemistry in this country, appeared during this decade, especially toward the latter end. The American journals of the period, The American Chemical Journal and the Journal of the American Chemical Society, published scarcely anything of a physico-chemical nature until somewhat later. For example, in the year 1895 only one paper of a definite physico-chemical character was published in both journals. To meet the growing interest in physical chemistry of this day, Professor Banqoft of Cornell, recently returned from Nernst's laboratory in Berlin, founded the Journal of Physical Chemistry. The first issue of this journal, however, did not appear until October, 1896. The beginning student in an American university of this period was in a measure, then, dependent upon his own resources if the field of physical chemistry were of interest to him. Textbooks, such as Remsen's "Advanced Inorganic Chemistry," were available and were, as we shall see, capable of stimulating productive thought. By 1895 The University of Kansas was twentynine years old, possessing a t this time a faculty of some fifty members and a student body of approximately seven hundred of collegiate rank. The department of chemistry had a staff of three members and was housed in its own laboratory building. Laboratory and library facilities were, however, when compared to those of the present day, decidedly meager. Standard treatises on the chemistry of that day were available, but journal literature wa9 scarce. Of course, one should remember that the total volume of chemical literature in that period was very considerably less than at the present day. In the fall of 1893 there appeared at this University, from the plains of central Kansas, a nineteen-year-old boy who was already much engrossed with chemistry. This boy, Hamilton P. Cady, was so much interested in chemistry that by the time he was seventeen he had purchased with his own earnings Remsen's "Inorganic Chemistry," a supply of chemicals, some test tubes, and several evaporating dishes. Of necessity these were soon handled with respect and care, for when this supply was gone, time and money were required to replace the stock, and money was scarce. A balance and a barometer were constructed by this
ingenious youth, and with this equipment many of the experiments described in Remsen's book were carried out. Cady, then, when he appeared a t The University of Kansas, already had a working knowledge of chemistry. The chemistry staff in 189394 consisted of Dr. E. H. S. Bailey, the chairman of the department, Mr. F. B. Dains, assistant in HAMILTON P. CADY AS A SENIORIN chemistry (who THEUN~VERSITY OF KANSAS was t a k i n g t h e From a photograph taken in 1897. place of E, C, Cady had made considerable progress in his researches on liquid ammonia as Franklin, absent on an electrolytic solvent when this leave a t The Johns photwaph was taken. Hopkins University), andMr. E. C. Case, assistantin chemistry. After consulting with Dr. Bailey, Cady enrolled as a freshman, but his knowledge of chemistry was judged sutlicient to warrant his being enrolled in organic chemistry, a course which was then given in the junior year. By the end of his sophomore year Cady had made such progress that he was made an assistant in chemistry and the following year had charge of the laboratory of qualitative analysis. During the fall of 1895, Cady, then a sophomore, became interested in the water of hydration of salts, a topic of never-failing interest apparently to many generations of chemists. He prepared many such hydrates, especially those containing several metals. In attempts to establish the constitution of these hydrates, Cady reviewed the literature available, including his ever-ready Remsen. In Remsen's book1 he ran across this statement, I t is a curious and interesting, though at present inexplicable, fact that anhydrous copper sulphate combines with five molecules of ammonia iust as it does with five molecules of water. ~~~. and that hy lying in moist air thc molecules of ammonia in t h ~ compound arc succeasivrly replaced by rater. so that the following series of compounds is formed:
From this it would appear that the ammonia in these compounds plays a part analogous t o that played by the "water of crystallization." REMSEN,"Inorganic Chemistry," 2nd ed., revised. Henry Holt hi Co., New York City, 1890, pp. 5934.
This set Cady to work, looking up other possibilities. himself. But neither equipment nor liquid ammonia to see if the replacement of water by ammonia in hy- in quantity was available. He then took the project drates was a general phenomenon. As a result of this to Prof. E. C. Franklin* who encouraged him and study he reported before the chemical seminary of told him that his problem appeared feasible. Franklin the University on March 18, 1896, upon "Ammonia had developed into a very skilful glass blower and to Compounds Analogous to Salt Hydrates."* help Cady along made for him a small Dewar vessel Early in this study the possibility of using liquid with a wide mouth. Dr. Bailey, the head of the deammonia as an electrolytic solvent occurred to Cady. partment, was then consulted and he agreed to purchase Cady reasoned in this way: Water forms hydrates for Cady's use a cylinder of liquid amm0nia.t These last events took place in the spring of '96 with certain salts. This indicates a certain unsaturatedness of water. These same salts form analogous and, as the liquid ammonia was slow in arriving, no compounds with ammonia. Water dissolves these hy- further work was accomplished until the fall of that d r a t e s n o t only dissolves them-but in dissolving year. When school commenced again in the fall, the them produces a system which is an electrolytic con- cylinder of liquid ammonia had arrived and Cady** ductor. Possibly lipid ammonia would dissolve these began his actual experiments with liquid ammonia. salts, the solution of which might likewise conduct Dr. Franklin had been granted a year's leave of abelectrolytically. After reasoning in this fashion, Cady sence for the school year of '96-'97,tt so that Cady undertook to look up the meager literature available began his experiments without the aid or advice of the elder man. in the library a t his disposal. Weyl,= Cady's original e q u i p m e n t was S e e l ~ and , ~ Gore4 had all published comparatively crude. It consisted of some work on solutions in liquid an old ammeter, the Dewar tube ammonia, but none of these publicamade by Franklin and fitted with a tions was available to Cady. Forpair of electrodes, and a 110 d. c. cirtunately, Gore's paper had been abstracted in Watts' "Chemical Diccuit as his source of electrical power. tionary," a set of which was available His first experiment consisted in the measurement of current which would This abstract confirmed Cady's conjecture about the solvent ability of flow through liquid ammonia itself. He found, as far as he could tell by liquid ammonia, but, as Gore had not tried the electrical conductivity his ammeter, that it was a non-couductor. T h i s was surprising, a s of his solutions, Cady had no further Bleekrode7 had recorded that liquid information relative to his second ammonia was a good conductor of hvuothesis. The student of electroelectricity. As the result of his subchemistry will recall that this was before the days when the Nernstsequent work, Cady showed that Thomson rule6 had become suffiBleekrode had undoubtedly been cientlv well known to be included in usine a solution of an electrolvte the textbooks available, so that there EDWARD CmTIS AT (presumably a sodium salt) rather was no working principle to help BEG~NNINC HIS TEACHING CAREER than pure liquid ammonia. As soon as he found that liquid Cady 0ut.t The reader should also AT THE UN1vERsln OF KANSAS recall that this was before Waldeno From a photograph taken in 1889. ammonia would not conduct a curbeean oublishine his fnliffnl work rent, he added a quantity of potassium on-the hemist& and electrochemistry of non-aqueous iodide, which Gore had recorded as being very soluble, solvents. to the liquid ammonia and found that the resulting As Cady could find no information upon the electrical solution was a very good conductor. He also observed conductances of salts in liquid ammonia, he considered the possibility of determining the matter for
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*From the secretary's book of The University of Kansas Chemical Seminarv in the ~ossessionof Prof. E. H. S. Bailev. .. former chairman df the depktment. a WE=, Ann. Physik, 121, 601 (1864). a SEELY, C h m . News, 23,169 (1871). ' GORE,P ~ cRoy. . SOC., 21, 140 (1872). THOMSON. Phil. Mag., 36, 320 (1893); NERNST, Z. physik. Chem.. 13, 531 (1894). t For that matter, the dielectric constant of liquid ammonia had not vet been determined and. in fact. the first determination of the dielectric constant was suggested by the conductivity experiments of Cady described herewith. See GOODWIN AND TROKSON, Phys. Rev., 8, 38 (1899). The &st of Walden's papers was published in Z. anorg. Chem.. 25. 209 (1900). For a c0mDkte summanr. see Walden's book, "~kktrochemie~ichtw%isser~geger ~osungen,"Johann Ambrosius Barth, Leipzig. 1924.
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was still a voum . - man and was Cadv's senior onlv. bv. some twelve years. 7 By 1896, liquid ammonia was an article of commerce. Professor Linde had constructed the first ammonia refrigerating svstem at Munich in 1873. After that time the refriaeration industry grew very rapidly, with the resultant increas; in the production of liquid ammonia. The Kansas investigators had a considerable advantage over Gore, who had to prepare his liquid ammonia by Faraday's process, i. e., decomposition of AaCI.2NHa and condensation of the ammonia thus formed in sdaled tubes. ** The reader willrecall that this was the beginning of Cady's senior year in college. tt Franklin took this vear's leave to enaaae .. in chemical work for mining company in-costa Rica. ' BLEEKRODE. Phil. Mag. 151, 5,384 (1878).
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two facts in connection with the passage of electricity through the t u b m n e was that the solution became blue around the cathode, and the other that i t became brown around the anode. The blue color he immediately recognized as metallic potassium, as Gore had stated that the alkali metals were soluble in liquid ammonia and gave blue solutions. Cady next turned his attention to solutions of these alkali metals in liquid ammonia. He soon found that sodium dissolved in liquid ammonia was an excellent conductor and this led him to speculate concerning the mechanism of the conduction. The idea soon occurred to him that here was the possibility of decomposing an element. As far as Cady knew there was no other case on record where an element dissolved and gave a conducting solution, and in all conducting solutions of which he had any knowledge, chemical changes resulted from electrolysis. It is not to be wondered then that it was with considerable interest, bordering on excitement, that he undertook a quantitative study of the passage of electricity through liquid ammonia solutions of sodium. He found to his surprise and disappointment, however, that no decomposition of sodium took place--even after passing as many as twenty Faradays per gram atom of sodium there was no decomposition apparent. The explanation of this phenomenon was really a more difficult task than the more logical "decomposition" of sodium would have been. Cady explained it satisfactorily, however, and the explanation has stood the test of many careful experiments in the years since that day. His reasoning and explanation were as follows: Apparently the conduction of electricity in this solution did not follow Faraday's law, but metallic conduction also did not follow Faraday's law. Possibly this was a conductor of the first class (i. e., a metallic conductor). Conductors of the first class are further characterized by the fact that no polarization occurs where the current enters and leaves such systems. If sodium in liquid ammonia is a conductor of the first class, then there should be no polarization a t the electrodes. This was tested out by passing a current through the solution, interrupting the current momentarily and observing if any back e. m. f., or current in the reverse direction, was noted. None was observed and hence Cady concluded that the conduction was analogous to metallic conduction. Cady also showed a t this time, while working with sodium, that its solutions could be extracted of their sodium content by shaking with mercury, forming sodium amalgam, and that no mercury passed into the liquid ammonia to compensate for the sodium extracted. This was undertaken to show, as conclusively as possible, that sodium existed in these solutions as metallic sodium and not as a sodium compound, which might possibly have been formed as the result of chemical reaction between sodium and ammonia. Upon the basis of his knowledge gained thus far, Cady presented a paper before the Kansas Academy
of Science which met in Topeka on December 31, 1896. It appeared on the program as "Water of Crystallization and Experiments with Liquid Ammonia."s I t recounted in a somewhat similar fashion to that presented in this paper the beginning of the work in liquid ammonia. Cady's first paper in this field of liquid ammonia research was published in April, 1897.9 I t was entitled "Action of Liquid NH3 on Iodine," and apparently was suggested by the formation of the "brownish coloration" a t the anode in his electrolysis of potassium iodide. His results showed that there was actual reaction between iodine and ammonia. Cady's next efforts were directed toward obtaining a more exact knowledge of the conductance of salt solutions in liquid ammonia. The conductances were measured by the usual Wheatstone bridge arrangement, using the old familiar buzzer as the means of securing an alternating current of high frequency and pasting strips of paper on his Dewar tubes to calibrate their volume. This arrangement, while crude in the light of present-day equipment, served its purpose and the results which were obtained compare favorably with the data obtained later by Franklin and Kraus with more elaborate equipment and greater precautions. The results of these experiments were published by Cady in the fall of 1897 under the title "The Electrolysis and Electrolytic Conductivity of Certain Substances Dissolved in Liquid Ammonia."lo His results indicated that many salts were better conductors a t the same concentration when dissolved in liquid ammonia than when dissolved in water. He suggested that the most probable explanation of this increased conductance was a greater ionic mobility in the first solvent, a speculation which he and Franklin later verified. In his studies upon salt hydrates Cady had prepared some of the hydrates of hydrogen chloride a t low temperatures. HC1.3Hz0 and HC1.2Hn0 were known, but HCl.HzO had not been isolated. The fact that HC1 formed h v d r a t e s suggested t o Cady t h a t ammonium chloride was i n effect HCl.NH3, i. e., hydrogen chloride with one mole of ammonia of crystallization. This in turn suggested the possibility t h a t ammonium salts in general in liquid 8 Trans. Kens. Acad. Sci., 15, 38
(1898). *CADY, Kans.
Univ. Quarterly, Series
A, 6, 71 (1897). lo CADY, J Phy~. C h a m . , 1, 707-13
PROPESSOR K~nusFROM
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ammonia would have acid properties. C a d y soon tested this out and found that ammonium salts in liquid ammonia r e a c t e d with metallic magnesium, liberating a gas. The gas was collected and found to be hydrogen, i . e . , ammonium salts in liquid ammonia produce hydrogen when allowed to act upon magnesium Pnomsson CADPFROM A RECENT AS is well known, P~ra.rocnn~a this is one of the characteristics of acids in water solution, and hence Cady felt that he had confirmed his conjecture concerning the acid character of ammonium salts. This property, discovered by Cady, suggested other possibilities to Franklin and in later years aided him (Franklin) in the development of a comprehensive system of compounds in this solvent. Cady also recognized a t this time the possibility of using liquid ammonia solution of sodium as a powerful reducing agent. He found that many organic compounds, particularly halides, were reduced by the solution. Dains" aad his students subsequently developed this procedure as an alternate method for the tedious Carius process of determining halogen in organic compounds, as the halide is converted into the sodium salt by the action of the metallic sodium in this solvent. The student in this field will also recall the extensive applications of this reducing agent in the hands of Kraus, White, and their co- worker^.'^ The years of 1895-97 were thus seen to be particularly fruitful in the development of this new field. These developments, it should be remembered, were initiated by a college youth in his junior and senior years in an institution but little past the frontier stage and hence without large library and laboratory facilities. Educators, if they compare the product of the modem college with the achievements of this senior, need not find in the comparison a sad commentary upon their efforts. Rather, such acbievements reflect more credit upon the intellectual capacity of a student who is able to give birth to such ideas and who possessed the manual ability and tenacity of purpose to rear such ideas to the stature of a wellformed field of research. Cady was graduated from The University of Kansas in the spring of 1897. Through the efforts of the
chemistry department he was offered and accepted a scholarship in chemistry at Cornell for the school year 1897-98. At Comell he worked under the direction of Professor Bancroft. Cady had hoped to continue his work on liquid ammonia a t Cornell, but Bancroft had just finished his book on the phase rule and consequently was much interested in the field of heterogeneous equilibria. Cady was accordingly set to work in this field, became interested in it, and made such progress that the following year he was promoted to a fellowship. It was during his stay a t Cornell that he published the paper "Electromotive Force between A r n a l g a m ~ "which ~~ contains the equation known to workers in this field as "the Cady equation," an equation which was subsequently verified by Richards and his students.14 Franklin returned to Kansas the year that Cady left, in the capacity of professor of physical chemistry. He followed Cady's experiments with considerable interest and, when it became apparent that Cady was not able to continue the work in this field a t Cornell, asked Cady if i t would be permissible to continue some of Cady's experiments in liquid ammonia. The permission was readily granted and Franklin set to work examining solubilities of a number of compounds in liquid ammonia. His work soon attracted the attention of a student in the engineering school. This was Charles A. Kraus, who was a t this time (school year 1897-98) a senior in electrical engineering. Although Kraus had elected to study in the field of applied science, he had soon become interested in pure science. In his junior year, for example, he, together with two instructors in the physics department, published an account of the Zeeman effect.16 This was one of the earliest studies made of the Zeeman effect in this country, being antedated only by the work of Professor Michelson of Chicago. In the fall of 1897 Franklin and Kraus joined forces and decided to undertake a comprehensive survey of the solubility of substances in liquid ammonia. As a result of their studies they were able by June of 1898 to submit a paper to the American Chemicnl Journal, containing the record of the qualitative and approximate quantitative solubilities of over five hundred substances in this solvent. Some of this work confirmed Gore's original observations, but much of it was a considerable extension over that of Gore's work. This paper was published in the December number of the American Chemical Journal for 1898 and has been exceedingly useful to all workers in this field. This joint paper was followed shortly by three others: "Determination of the Molecular Rise in the Boiling Point of Liquid Ammonia" (also in the December issue of the American Chemical Journal, 1898) ; "Metathetic Reactions between Certain Salts in Solution in Liquid Ammonia"; and "Some Properties of l a CADY, J. Phys. C h . ,2, 551 (1898). Carnegie Inst. Pub. Nos. 56 and 118. DUNSTAN, RICE, AND KRAUS,"The Effect of Magnetism upon the Spectral Lines of Sodium," Kans. Unit,. Quarterly, Series A, 6, 77 (1897). l4
DArNs, 3. Am. Chem. Soc., 40, 936 (1918).
'1 la KRAUS.ibid., 45,
for 1923 and 1924.
768 (1923); WHITEand hisstudents, ibid.,
without getting results, even putting in their noon hours upon the task that they had set for themselves, Mrs. Franklin bringing them their lunches. With Journal. Kraus continued on at Kansas after his graduation such persistence, the required technic was at last gained for a year of graduate study and as a result still another and the measurements followed each other in rapid joint study upon the conductivity of solutions in liquid succession, their results showing that ionic velocities ammonia was made. These measurements were car- were considerably greater in liquid ammonia than in ried out with more precision than Cady's original water." After the completion of this work, Cady started measurements, Cady having called attention t o the fact that his values were only approximate and needed work upon his doctor's thesis. Under Franklin's revision. The results of this studv were published direction this was finished in the spring of 1903 and in 1900.'8 was a study of concentration cells in liquid ammonia.Is Kraus left The University of Kansas in the spring The following year (190344) Professor Franklin was of 1899 with a record of marked achievement in help- called to Stanford University, where he has remained inc to oDen UD this new field of research. The reader until the present day. His subsequent researches, will again notice, if he has not already done so, that as well as those of his many students, in the field of a very considerable proportion of the work done by liquid ammonia are well known. His election to the Kraus was done while he, too, was in his senior year presidency of the American Chemical Society in 1923 at Kansas. Kraus's interest in liquid ammonia after and the awards of the Nichols medal in 1925 and of the Willard Gibbs medal in 1932 leavinc Kansas was not lost and after 1907 the publications of this iuvesare recognition of the worth of these fundamental researches. tigator in this field continue in an Cady became Franklin's successor almost uninterrupted flow until the at The University of Kansas and present day. His well-deserved place among the foremost chemists has remained there since. His work subsequent to the departure of Proof the day needs no further mention fessor Franklin has been in several here.* fields. His co-discovery, with McI n the spring of 1899, Cady, after a two-year stay at Cornell, was Farland, of the presence of helium offered an assistant professorship at in natural gases of Kansas has been his alma mater and accepted, reone of the most outstanding of his achievements. In recent years he turning to The University of Kansas and his students have again turned in the fall of 1899. By that time their attention to the field of liquid the studies of Franklin and Kraus ammonia research, attention having were wen under way and were givbeen paid chiefly to the electroing promise of many interesting results. Cady was eager to renew his chemistry of liquid ammonia solutions and to phase rule studies in work with liquid ammonia. After talking with Franklin, they decided P~OPBSSOR FRnNKLrN FROM A RECENT this solvent. Pmr-roc~n~rr to study the velocity of ionic migraFrom the foregoing pages it is hoped that the idea has been developed that tion in this solvent. I t will be recalled that Cady had suggested that the increased due credit should be given to three men for the present conductance of salts in liquid ammonia was possibly position of liquid ammonia research in this country-to due to a greater mobility of ions. It was some Cady as the initiator of this work; to Kraus as the time before actual work was begun, but finally skilled experimentalist and elaborator; and to Franklin Franklin and Cady started work together upon this as the organizer of this body of learning. To all three investigation. Both Franklin and Cady regard this men credit should also be given for their ability as work as their most difficult experimental study in this teachers. All of them have been able to attract large solvent. The method which they adopted for their numbers of students to this field. As a result, many of study was that of measuring the velocities of moving the scientific "children," "grandchildren," and possibly boundaries, the work requiring the placing of three even "great grandchildren" of these men are themselves solutious together in a tube in such a fashion that a making contributions to this field of learning. In the last place it should be said that it would be sharp and distinct surface of separation occurred between the solutions. Only those who have had oc- difficult to find a group of three men who were so casion to work with solvents of low boiling point can kindly in character, so upright in purpose, and so keen appreciate their difficulties. They worked for weeks in insight as these three founders of this field of research. To this statement their many students will " F R A N ~ AND ~ I NKRAUS, Am. Chem. J., 23,277 (1900). * The contributions of Kraus and Franklin to this field have all agree. been well summarized in the reviews of Femelius and John- son appearing in the issues of the JOURNAL OF CHEMICAL EDUCACADYAND FRANKLIN, 1. Am. C h m . SOC.,26, 499 (1904). TION during the period 1928-30. CADY, J. Phys. C k . , 9 , 476 (1905).
Liquid Ammonia." These last two appeared in the January, 1899, number of the American Chemical
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