Jacob Green's Chemical Philosophy: Insights on the teaching of

Jacob Green's Chemical Philosophy. Insights on the Teaching of American College Chemistry 160 Years Ago. David W. Kurtz. Ohio Northern University, Ada...
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Jacob Green's Chemical Philosophy Insights on the Teaching of American College Chemistry 160 Years Ago David W. Kurtz Ohio Northern University, Ada. OH 45810 Most of the "Founding Fathers" of American chemical science have been chronicled in recent years, particularly those of the Philadelphia School (I).The accomplishments of Benjamin Rush, James Woodhouse, Samuel Latham Mitchill, Benjamin Silliman, Robert Hare, and others associated with the Universitv of Pennsvlvania are relativelv well known, having heen presented several times in the pages of this Journal 121. chem, . However. one leadine Phlladelnh~an ist generally neglected in recent discussions of American chemical history is Jacoh Green. The lack of notice given him is the more puzzling because of his prominence during his professional career (1818-1841). He authored 10 hooks, six of them university science texts, studied a t the University of Pennsylvania and a t the Sorhonne (under Gay-Lussac), taught a t the New Jersey College (later renamed Princeton) and the Jefferson Medical College, and was a prominent member of the I'hiladelphia scientific community until his death in 1841. Some biographical highlights are listed in Table I. This Daoer is offered for the occasion of his 200th birthday annivkshy, July 26,1990. Path to Professorlate Green seems t o have been somewhat precocious, having taken his BA from the University of Pennsylvania in 1806, before his 17th birthday. Since his father and grandfather were both presidents of Princeton (3),his eventual choice of an academic career is not survrising. As an undermaduate he was interested in medicine, but instead hecame an attorney, wasadmitted to the Pennsylvania Bar in 180&and practiced law for the next decade. At University of Pennsyivania he studied under James Woodhouse. While Silliman had a poor oninion of Woodhouse (remarkine that ". . . He anneared . when lecturing.. . as if fearful he was not highly a G e c i a t ed-as indeed he was not verv hiehlv") . . (41. . .. Woodhousemust have had good effect on ~ a c d ha, h o took his first postgraduate year to coauthor a treatise on electricity, delaying by a year his admission t o the bar. One wonders what Jacoh would have done had eraduate studv science - in ~hvsical . been available in ~ m e r i c athen. The next decade of Green's life is voorlv documented. It is known that he traveled widely in addition to practicing law in Philadelphia. During this period he made the botanical collections that enabled him to publish Catalog of the Plants Indigenous 10 theStateofNew York (1814) and later Botanj of the United Stales (1831). It was in 1818 that he took up his first academic post, appointment as Professor of Chemistrv. Philosonhv. ".Ex~erimental . . .. and Natural Science at Princeton. He remained there four yean, accepting the Chair of Chemistrv at Jefferson Medical Colleee in PhiladelS the position from which Green's phia in 1822. T ~ was major contributions were made. In 1827 after publishing Electromagnetism, he traveled in France, England, and Switzerland, where he met most of the luminaries of the British and French scientific communities. Many authors have underscored the pivotal role of medical studies in this phase of American chemical sciences (2). While more than a dozen nonmedical institutions had adopted chemistry as a course of study by 1820, in America, 186

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Table 1. Chronological Framework ol Jacob Green's Career Jacob Green, b. July 26, 1790 1806 . B A. University of Pennsylvania 1808 Epitome on Eiecnicilyand Galvanism (with E. Hazard) 1808-181s Practiced law I818 Professor 01 Experimental Scoence. Princeton 1822 Chaw 01 Cnemlsq. Jefferson Medocal College 1827 Eiectmmagnetism 1827. 1828 Travels in Europe 1829 Chemkal Dlsgram* A Tenbook 01 Chemkal PhIImphy 1830 Not- of a Traveier,AsnonomlcalRscreations 1831 Botany of the United States 1832 Monogrrrph of Trilobites of North America 1835 Syllabus of a Course In Chemishy 1841 Diseases of lhs Skin Died February 1. 1841. Philadelphia

unlike Britain and Europe, chemistrywas perceived almost exclusively as a basis for medical studies rather than as a developing discipline of its own. The result was that in the United States the evolution of chemistrv into a distinct quantitative science occurred in medical i&itutions. Green was one of the midwives during this labor, and his maior t of Chemical phiinstrumentality was his text, A ~ e rBook losophy (henceforth Chemical Philosophy), first published in 1829. Narrowly observed, this text was not remarkable. I t was in major part a reworking of Edward Turner's Elements of Chemistry (1827), which had already been released in two American printings. A widespread practice of the day was to quote directlv from earlier treatises in extended works of one's own (5): Green acknowledged his debt to Turner, both on the title vaee of Chemical Philoso~hvand in its nreface. going so f & a s to say, "The languagk in Dr. ~ u r n e r ' s~ l e : ments has been preserved so far as is practicable." Arnerlcan College Chernlstry In 1830 Several original factors make the work a striking departure from Turner's book, however. First, Green edited and rearranged suhject matter to make it accessible to untutored beginners in physical sriences. Green's preface says of Turner's hook that . . . The princrpal objection to rhisexrellmt work seems to be that in irn arrangement many facts unknown 1,) heginners are adduced at its very commencement as illustratima of principles.. .The arrangement of the principles and the facts as it now appears [i.e., in Green's text] belongs to the present author and whatever praise or blame attaches to this is to be attrihuted exclusivelv to him. It is s plan which has been pursued by him for many years in the teaching of the science, and is one which seemed naturally to rise out of the progress of discovery. Second, Green reorganized the presentation of salts, placing the description of each well-characterized salt with that of its principal metal. He intended a full descriptive chemistry of each element, comparable to Cotton and Wilkinson. Fifty elements are listed, and some of the trends that today are called periodic uariations are noted. Third, Chemical Philosophy incorporated a separate section of 150 pages devot-

ed to organic chemistry. Fourth, new compounds and elements from recent literature were included in Green'n work. Indeed. aluminum. vttrium. and bervllium (elucinum). which were discove& by ~ 6 h l e in r 18i8, are dLcussed in this text. ~ u b l i s h e din Philadeluhia in 1829. Finallv. a companion book of visual aids was used with the text; it was entitled Chemical Diagrams and published as a separate volume (1829). Bound with the text is an appendix of surprisingly good molecular weight equivalenta ("chemical equivalents"); about 400 are listed. Taken together, these innovations remove Green's Chemical Philosophy from the category of treatise and make i t a college textbook in the modern sense of the word, i.e., less an erudite and exhaustive reference work for the savant than a thorough introduction and survey for beginners. The oreanization of the work affords considerable insieht into the $evelopment of college chemistry teaching a t a m k t crucial epoch (6).Three revolutions were transforming the warp and woof of chemistry in this period. These were the firm a d o ~ t i o nof Dalton's atomism as more than a basis for stoichiometry, the incipient articulation of thermodynmics. and a search for svstematic relationshius m o n e the properties of the elemehts. None of these changes was yet comulete or universallv accepted. How was chemistry taueht in the absence of a comprehensive theory of atomicweights and constitution, conservation laws in energetics, and a beuristic model with which to correlate electrtcal and physical properties? Table 2, a transcription of the "Table of Arraneement" from Chemical f'hiloso~hv. . - . demonstrates the eenera1 approach. Part I first considers physical forms of matter and Part I1 energetics (caloric, light, and electro-magnetism) under the rubric of "imponderat~lematter", i.e., m a t w with no detectable mass. Prior consideration of electrical phenomena is essential for the next and main Part of the work, the five divisions (,f Part 111 dealing with "ponderahle matter". Here elements are classified as electronegolive or electroposiri~~e hased on which pole of a battery they migrate toward, no distinction heing made between an element and its ions. Metals are considered after representative elements, and nonmetals and are subgrouped according to the acid/ base properties of their oxides. The descriptive chemistry of the haloeens (the second throueh fifth "electroneeative bodies") i s i h e last discussed, t h e n p a r t 111ends witLtheoretical rationales of definite proportions, including Dalton's atomic theory and Gay-Lussac's theory of gas volumes. Part IV is a treatment of organic chemistry, the tone of which is evident from its introduction: Such [inorganic]substances are characterized by containingsome principle peculiar to each. Thus the presence of nitrogen in the nitric and sulfur in the sulfuricacid establishes a wide distinction between these substances; and although in many instances two or more inorganic bodies consist of the same elements,. . . they are always few in number and distinguished by a well-marked difference in the proportion in which they are united. The products of animal and vegetable life, on the contrary.. . are nearly all composedofcarbon, hydrogen, and oxygen, inaddition to whichsome of them contain nitroeen.. .In point of composition, therefore, most organic suhstanees differ only in the proportion of their composition, and on this account may not infrequently he eanverted into one another. ~~~~

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Althoueh Wohler's urea svnthesis is described. vitalism is never m o k e d or rejected; instead a reductionist "iewpoint is assumed. The 150 pages of organic chemistry are mainly concerned with descriptive chemistry and analytical/stoichiometric accounts of organic substances, especially those used in medicine a t the time. Atomfc Theory A deep skepticism still pervaded academic chemistry about the reality of atoms as ultimate particles. This was partly because many pure compounds that had earlier been

regarded as elements later had been demonstrated to contain simpler substances. There are but few substances in nature which can be considered as elements. The term element is used as synonymous with undecompounded body; in modern chemistry [!I its application is limited to the results of experiment. The improvements taking place our in the methods of examinine bodies are eonstantlv chaneine " opinions with respect to th& nature, and there :s no reason to suppose that any real indestructible principle has as yet been discovered.

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T h e tenn bodv was used to evade the ouestion of whether a pure chemicai substance was an element or compound. Even the status of sulfur as an element was still questioned:

.. .Sir H. Davy found likewise that when an alloy of tellurium and ootassium was acted uoon hv,melted sulfur. telluretted and sulfu~~,~~ . retted hydrogen equal toat least HO times the volume of the sulfur were dlaengayed. He made many experiments of this kmd, the sulfur heing rwentlgauhlimed in nitrugen gas, and moisture being excluded with the greatest care.. . it might be supposed that [the hydrogen] might belong to an accidental admixture.. .hut the proportion is too large.. .and it seems more probable that it arises either from the decomposition of the sulfur, or the metals, or of all three. We know nothine of the true elements heloneine to nature, but as fnr as we Can reason from the reactions or the pn#peniesofmatter, hydrogen is thesuh~tancewhich approaches nearest to what the elements may he supposed t u be.

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This apparently unreconstructed passage of Turner's is offset by Green later in Chemical Principles in a discussion of Dalton's theory: We have onlv. in fact. to assume with Mr. Dalton that all bodies arecompo~edofultimiteatomstheweight of which isdiilercnt in

different kinds of matter, and we explah at once the foregoing laws ot chemical union. The phenmnena do not appear explicable on any other supposition.

Table 2.

Table 01 Arrangement lrom Chemlcal Phllorophy

Part I Powers and Properties of Matter Chemical changes, fwms, gravitation, cohesion, chemical anractian part I1 imponderable Matter Caloric, light, elechicihl magnetism. Part Ill Ponderable Matt? Division 1 First Elechonegative Body and its Comblnations. Chapter 1. Elements reclp rocally combinlng. ovaen Nitrogen Hydrogen Carbon

Chapter 2. Elements Which Combine with Oxygen and Hydrogen Boron, silicon. zirconion. sulfuron. ~ho~~horon. . . selenion,tellurium, arsenlcum, stannum. potassium Chapter 3. Metals Producing Alkalis. Sodium. lithium, barium. stronllum, calcium, magnesium Chapter 4. Metals Producing Acids. Volume 68

Antimonium, chromium, manganesum, molybdenum, tungsten, coiumblum. titanium, uranlum aurum Chapter 5. Metals Producing Oxides. Plumbum, ferrum, cuprum, mercurium, cerium. platinum, cobaltum, nicoium palladium, rhodium, iridium osmlum, plursnium, zlncum cadmium. bismuthum. argentum,aluminum, giucinum, yttrium. Division 2. Second Elechonegative Body and its Combinations. Chlorine Division 3. Third Elemonegative Body and ih Combinations. Iodine Division 4. Fourth Electronegative Body and its Comblnations. Bromine Division 5. FlRh Electronegative Body an0 its Combinations. Fluorine Atomic Theory ofDanon Gaylus4ac's Theory of Volumes Theory of Berrelius ConstiMEon of isanorphous Ssns Part IV. Organic Chemistry Part V. Analytical Chemistry Aooendicss

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And again, Though the phenomena of chemical combination leave little doubt of the atomic constitution of matter, other powerful arguments may now be adduced in favor of this theory.. ..Another argument which amounts almost to a demonstration is deducible from the peculiar connection noticed by Professor Mitscherlich between the form and composition of certain crystalline substances. But in adopting the notion that matter is composed of ultimate individual ~articles.we are bv no means satisfied of the nrnnriatv of exnrea~inethe facts of the science in laneuaee -..-. ~..< .~ " .. founded on this theory: hecause, rhough elements of hodies be arranged atomirally, we have no certain method of ascertaining, in the present state of chemistry, bow many atoms are contained in any compound. ~~~~~~~~~

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T h a t these later sections of the text are Green's original work is indicated by Green's comments on conversations he had with Dalton and Gay-Lussac during his European travels in 1827. Both the position and the tenor of Green's comments on atomic theorv indicate that he was more firmlv attached to Dalton's atomism than was Turner, who stiil s u s ~ e c t e dall metals and other combustible elements contairied hydrogen. Therrnodynarnlcs And Physlcel Reletlonshlps Although thermometers are amply discussed and routinely employed in the text, consenration laws were only implicitly recognized. Chemical Philosophy still terms heat caloric, and discusses it as if i t were a form of matter: Caloric, on the supposition of its being material, is a suhtile fluid, the partides of which repel one another, and are attraded by all other aohstanees .. . .We wish. at the same time. tostatedistinct.....~ ~ly, that we do not believe that heat. light. electricity, and magnetism are material substances, we only speak of them a3 such because this hypothesisis the most convenient one under which 10 arrange the facts that have been collected. ~

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Disbelief in the material reality of caloric without an adequate replacement for particulate caloric pewaden the dis&ssion of heat capacity The same quantity of caloric which heats a pound of water one degree, will heat an equal weight of spermaceti oil two degrees, and therefore water is supposed to contain twice as much ealoric as oil. Dr. Black was the first tonotice this remarkable difference, and he expressed it by the term capacity for calorie. The word capacity was probably suggested by the idea that the capacity of a body for caloric depends upon its capaciousness, or the distance between its particles, in consequence of which there is much more room for caloric.. . .But as Dr. Black himself pointed out, if this were the real cause of the difference, the capacity of bodies for caloric should vary inversely as their density. Thus, since mercury is thirteen times and a half denser than water, the capacity of the latter for ealoric ought to be thirteen times and a half greater, whereas it is 28 times as great. And the nature of a heat capacity is still not clear: To heat an equal weight of water and mercury by the same number of degrees, it is necessary to add twenty eight times as much heat to the water as to the mercury; which proves that a quantity of caloric becomes insensible to the thermometer when the temperature of water is raised by one degree, just as happens when ice is converted into water. or water into vanour. The two phenomena ~-~~~~ are so far identical; &d consequently if an attempt be made to arrnnnt. for nne of them. ..... ...-,-it is necessarv to adoot some exnlanatian that shall apply equally to the other. No plausible the& bf this kind has been proposed; and therefore it is better to be satisfied with a simple statement of the fact ~

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Lack of a kinetic molecular framework here obscures the distinction between heat capacity and phase transition, and raises paradoxical questions about the relationship between temperature and heat. I n a text ~ u b l i s h e din the first half of the 19thcentury, one might exp& considerable discussion of steam and steam engines, the study of which was then propelling thermody-

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namics toward its mesent mathematical elezance. Such expeetations are shattered in Green's book, which contains a scant two . paramaphs on the subject. On the whole i t is fair to .. say that neither the incipient theory nor the practical applications of thermodynamics were yet regarded an fundamental to a collegiate exposition of chemical phenomena. Toward Perlodlc Relatlonshlps The 50 elements or "undecompounded bodies" described in ele--- Chemical Philosoohv included all the re~resentative ments (except for tde noble gasses), the first four halogens and chalcoeens. all the ~ n i c o e e n (Groun s VA), all of the first transition, most of the second and third transitions. Group 1 above rubidium. and all of Group 11 except radium. Clearly this is enough tb set the framework of p&iodicity, and it is fair to ask whether progress - - was being- made in that direction. Table 2 shows that the electronegativity of the halogens had already set them off as a separate group. Other periodic relationships had been remarked by Mitscherlich prior to 1820. As Green explained it: It appears from [Mitscherlich's] researches that certain substances are capable of being substituted for each other in combination, without influencing the form of the compound.. .. Each arseniate has a corresponding phosphate possessed of the same form, and containing the same number of equivalents of acid, alkali, and water. These series of salts, in fact, differ in nothing but one containing arsenic, and the other phosphoric acid. ...This discovery has lead to the formation of groups, each comprehending substances which crystallize in the same manner, and which are hence said to be isomorphous. The oxide of lead, baryta, and strontia, when combined with the same acid, lead to salts which are said by Professor Mitscherlich to be isomorphous. The salts of lime are isomorphous with those of magnesia.. .the salts of selenic and sulfuric acids, when similarly united with water and the same base, assume the same form, and the salts of the peroxide of iron are isomorphous with those of alumina. Here we see, in spite of overemphasis on crystal form as a classifying criterion, the beginnings of a useful heuristic. Note that i t is aDDlied both to metals and nonmetals. A major fault of the Mitscherlich's correlation is that it confuses chemical elements with their ions. That source of confusion is eliminated in a section titled, "On the Analogies Between Elementary Substances". This section suggests that all "electropositive" elements are part of a single continuum: Potassium and platinum, if we except their lustre, colour, and power of conducting electricity, are bodies extremely dissimilar; yet by arranging the metals in the order of their natural resemblances, the two substances may be made parts of one chain of natural bodies: potassium, sodium, and barium are very like each other; barium approaches to manganesum, zinc, iron, tin, and antimony. Platinum is analogous to gold, silver and palladium; palladium is connected by distinct analogies with tin, zinc, iron, and manganesum. Here we see the metals treated as a list instead of a table. The grouping of K, Na, and Ba, although inferior to Mitscherlich's suggestion, is useful. T h e conceptual leap of using valence as a second dimension to transform the list into a table remains unguessed, however. That the large number of metallic "bodies" caused sharp concern to Turner and Green is evident in the ~ r e v i o u s ~-~~~~ cpotationa about the ultimate nature of elements. 1jeep suspicion remained that all inflammable elements were ultimately compounds of hydrogen and some other unknown orinciole. Such suspicion was especiallv understandable in ?urn&, whose major research was to &isprove the proposition that the weights of all elements were in simple whole number ratio (Prout's hypothesis). This refusal to believe in such a large number of ultimate particles (elements in their paradigm) is reminiscent of the unease that arose in particle physics 30 years ago during the meson boom. In both in-

stances the discovery of too many ultimate particles resulted in skenticism about the model without its immediate replacement by a more fundamental model. Hut in the earlier case. the well founded skepticism about how fundamental a model with 50 or more ''&maten particles could he, combined with the tendency to group elements as lists instead of tables (one-dimensional rather than two-dimensional search) forestalled formation of a true periodic hypothesis. The soohisticarion of Green's Textbook of Chemical Phi.=losophy, now over 160 years old, is surprising. Part of the nurnrise is due to its use of familiar terms such as "electronegative" or "chemical equivalent". While such terms have since been redefined. their functionalitv remains largelv unchanged. The attention bestowed o n texts like ~ a & e t ' s Conuersations on Chemistrv gives the impression that teaching materials used in Aiehcan c o ~ ~ e ~ ethis s b fperiod were inherently qualitative and descriptive. Chemical Philosophy, withi& quantitative argum&s and theoretical horizon, corrects any such impression. The volume is, like most American chemistries of the day, based on a British ~

nroeenitor. but in this case the rearrangements, additions, ;Id-changes of emphasis place Green's stamp clearly on the result. Most outstandine: in this respect is Green's adoption of unrestrained ~ a l t o n & ntheory i n the face of ~ u i n e r ' s nagging suspicious. Green, like many American scientists of his day, was an eclectic who applied European tools to the vast storehouse of American biological, geological, and mineral resources. Like Silliman, Green's publication record in journals was desultory, but his total scientific output quite possibly transcended that of any of his American contemporaries in spite of Green's early death. Certainly Jacob Green deserves inclusion in the first rank of nineteenth century American chemists. Literature Clted I. Beer, J. J. J . Chem.Educ. 1916.53.405. 2, lei Fay. P. J. J . Chrm. Educ. 1931,8,1533: lbl Newell. L. C. J. Chem. Edur 19R,53, 402. 3. Baker, H. B. in Dictionon o/ Amerieon Biography; Johnson, A.: Malone, D.. Ed%; Seribnar's: New York. 1931: Vol. 7, p 548. 4. Smith, E. F. Jomea WoodhousPhiladelphis, 1918: p 74. Quoted in ref 1, P 407. 5. Miles. WLibrary Chronicle 1952,18.51. 6. Lippineott, W . T . J . Chsm.Edue. 1976,53.401.

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