Carl Friedrich Mohr and analytical chemistry in Germany

Talama. Vol. 26, pp. 609 to 617

0039-9140/79/0801-0609502.00/0

Pergamon Press Lid 1979. Printed in Great Britain

CARL FRIEDRICH MOHR AND ANALYTICAL CHEMISTRY IN GERMANY FERENC SZABADV,~RY

Museum for Science and Technology, Kaposv~r u. 13, Budapest Ill7, Hungary and ROBERT A. CHALMERS ®

Chemistry Department, University of Aberdeen, Old Aberdeen, Scotland (Received 20 April 1979. Accepted 30 April 1979)

Summary--A brief account is given of the work of Mohr, which is set against the framework of the development of analytical chemistry in Germany from early times up to the present.

Carl Friedrich Mohr was born on 4 November 1806 in Koblenz, and died on 28 September 1879. Several biographical sketches have appeared, m-s and his long correspondence with Liebig has been collected and published with a biographical note. 6 The author of some 250 papers and numerous books, he has been called t the "Father of Volumetric Analysis", but his work extended far beyond this field, though it is for his contributions to analysis that he is usually remembered. Mohr was a brilliant student, graduating summa cure laude in pharmacy, which was then rather a severe discipline, but instead of a university career chose to continue in pharmacy and run his father's business in Koblenz. At that time scientific research in Germany was regarded as the prerogative of the universities and professors, so Mohr would have been working outside official scientific circles. To some extent this disadvantage must have been offset by Mohr's long friendship with Liebig, and it was at Liebig's suggestion that Mohr asked about a professorship at Bonn, but failed to follow it up h time. When the failure of his business eventually forced him into teaching, it was Bonn that finally gave him his chair. Mohr undoubtedly had great inventiveness, and Mohr's salt (ferrous ammonium sulphate), the Mohr method of argentometric chloride titration, the pinchclamp, the Mohr burette (with a small bead inside a rubber tubing connection for improved control of outflow) have enshrined his name in the form of "household" words in analytical chemistry. Besides his own original researches, his great contribution to analysis was the publication of his famous textbook "Lehrbuch tier chemisch-analytischen Titrirmethode", which appeared in two parts in 1855 and 1856, and reached its eighth edition in 1913. He made a critical examination of many titrimetric methods, introducing improvements of his own, before incorporating them into this outstanding manual of practical instruction. Because of the few references given

in the book, the text frequently gives the impression that Mohr is describing his own discoveries, whereas the credit really belongs to others. Back-titration is an example. It is difficult, of course, to decide how far such instances are genuine rediscoveries made in ignorance of earlier work, and how far they are due to failure to acknowledge sources (a problem that exists even todayT). Black, for example, had described back-titration s before Mohr was born, and though Mohr might well have been ignorant of this paper (though it had been mentioned by Klaprothg), it is less likely that he was unaware of P61igot's paper, t° It is interesting to note that this paper was presented at a meeting of the French Academy of Sciences on 29 March 1847, and a translation ~t appeared in the issue of the Chemical Gazette for 1 May 1847--a feat that appears to be beyond the resources of modern abstracting services! Similarly Mohr appears to claim invention of normal solutions, though this is usually attributed to Ure, ~2 or Griffin, ~3 and Szabadvfiry t4 quotes Duflos as using in 1845 a normal solution ts (though he may not have realized it himself). However, in the 7th edition of the Lehrbuch, edited by Classen, it is firmly stated on p. 56 that the idea originated with Griffin, and use of normality certainly became more common after the appearance of Mohr's book. It has recently been discovered that in fact Griffin had known Mohr for many years, t6 and presumably they discussed the idea. Whatever the truth of the matter, Mohr himself has suffered from misattribution or rediscovery of his ideas. For example, it was Mohr who invented the Liebig condenser, t7 and Liebig only publicised it. Again, Mohr originated the idea of amplification reactions, oxidizing iodine to iodate with chlorine, the excess of which was boiled off before the addition of iodide and titration of the iodine liberatedJ a Curiously. Mohr was rather critical ~9 of Schwarz's use of thiosulphate 2° as a titrant for iodine: time has proved him wrong.

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Most of Mohr's ideas have amply stood the test of time, however, and some have a very modern ring to them. His method for folding filter papers 2~ is the one still used, his invention of the cork-borer 23 and discovery of the efficacy of a mixture of turpentine and camphor as a lubricant for boring holes in glass 23 have been an everlasting boon to experimental chemistry, his method of sampling brown stone 24 is essentially the one still used, and his sale of standard solutions (at 10 groschen for a litre of 1 N nitric acid, the same as the price of a 10-ml burette or a 100-ml standard flask) 25 anticipated modem trends by about a century (Griffin also sold standard solutions and this is perhaps another aspect of his friendship with Mohr). Mohr's comments on over-elaborate methods being developed when simpler ones were obvious '° will wake an echo in the minds of most referees and editors of present day papers. Besides analytical chemistry, meteorology, mechanics, geology, bee-keeping and wine-growing all received contributions from Mohr, in the form of books and papers. TWO of his less well known contributions are on the mechanical theory of heat. 27'2s One of these papers "7 appears with no author's name in the Jahresbericht written by Mohr for Liebig's Annalen, and is attributed to Mohr by Kahlbaum. a9 The other paper 2s was refused by both L~ebig and Poggendorf but was accepted by Baumgartner in Vienna. Mohr himself did not know it had been published until 30 years later? 9,3° These two papers appeared five years before Mayer's paper which is often regarded as the first in the field. The record was finally set straight by Planck) ~ Mohr was a sharp-tongued and argumentative character, severely critical of others, and it is possible that personal animosities may have led to some of his work being ignored; they certainly caused him difficulty, and there is a sad tale concerning Mohr's death. 32 Mohr was undoubtedly endowed with a great gift for invention and innovation, and was perhaps the greatest individual worker in titrimetry. In many ways he was ahead of his time, and so failed to gain full recognition of his genius.

one that could be expressed mathematically, in the sense of abstract generalization. 'Now it is well known to most practising scientists today that there is a difference betwecn numeracy (the ability to perform arithmetic calculations correctly and to understand the significance of the numbers obtained) and mathematical ability (in the sense of understanding the logical relationships between numbers), and that there is a certain amount of classdistinction between the two. It is fashionable since the advent of the computer and the cheap pocket calculator to despise the ability to do arithmetical calculations and to venerate abstract mathematics as the "queen of the sciences" (a title that is also claimed by theology). It is plausible to suggest that it was the desire to make chemistry "respectable" by development of mathematical theory that led to the decline in status of analytical chemistry, as analysis was regarded as a mere number-gathering pursuit, and was regulated to a subordinate position, with little or no attempt to relate its practice to theory and vice versa. Even Ostwald, who was the first to attempt to put analysis on a sound theoretical basis, presumably thought in this way, since he said in the preface to his book "Die wissenschaftlichen Grundlagen der analytischen Chorale" that analytical chemistry is the servant of the other sciences, at the same time subordinate but also indispensable. 33 Even today, when it is clear to those who can see (but not to those who will not) that correct analyses can oniy be consistently obtained if the underlying theory is thoroughly understood and properly applied, this attitude towards analysis persists in many academic circles, and it is perhaps not surprising that analysis is the Cinderella of chemistry (with no fairy godmother in sight). However, with the ever increasing demands made by modern technology and public opinion, there are signs of a resurgence of interest in analysis and Cinderella may yet come into her kingdom. THE EARLY YEARS

As we have just said, analysis was the basis of early chemistry, and Germany was the scene of many important developments. Thus we may mention Georg ANALYTICAL CHEMISTRY IN GERMANY Agricola (1494--1555) as one of the earliest workers The history of analytical chemistry in Germany is in the field of mining and metallurgical analysis--a in many ways a microcosm of the development of theme that recurs throughout the history of the subchemistry in general, and well illustrates the close ties ject and reflects the economic importance of analysis. Water analysis was another topic extensively invesbetween analysis and industry. It also raises speculation about the interaction of philosophy and analyti- tigated, and the names of Leonhard Thurneysser cal chemistry. The initial stages in the development (1530-1596, a student of Paracelsus), Andreas Libeof chemistry were necessarily occupied with gathering vius (1514-1616) and Friedrich Hoffman (1660-1743) of facts and classification, and analysis was an essen- span over a century of effort in this area. Johann tial part of the process. By its very nature, however, Rudolf Glauber (1604-1670) made many observations analysis is closely associated with numbers and quan- in the course of production of chemicals on a tification, and though Kelvin had a clear grasp of commercial scale, including the solubility of silver the prime importance of quantitative measurement, chloride in ammonia. Around the same period Otto Kan.t had earlier announced that a true science was Tachenius was developing tests for metals, and

Carl Friedrich M o h r

appears to have been a pioneer in biochemistry a n d toxicology.34 He also observed that strong acids displace weak. Most of the early work was necessarily qualitative, but an early piece of quantitative analysis was based on precipitation of silver chloride, by Johann Kunckel (1630-1703), who was also one of the pioneers of the blowpipe. This tool rapidly became indispensable in analytical work, rand its use was extensively developed by Georg Ernst Stahl (1659-1734), Johann Cramer (1710-1777) and Sigismund Andreas Marggraf (17091782), who was one of the early workers at the celebrated Mining Academy at Freiberg. Some,day we may be fortunate enough to have a history of this academy and its contributions to analysis. The sugar beet industry might well consider paying tribute to Marggraf for his discovery of the process for extracting the sugar. Another exponent of the blowpipe was Johann Heinrich Pott (1692-1777), who was engaged in an early example of industrial espionage in his attempts to find the composition of Meissen procelain. as Another name associated with the use of the blowpipe is Karl Friedrich Plattner (1800-1858), who was also at the Mining Academy. Goethe was taught to use the blowpipe by Berzelius. Carl Freidrich Wenzel (1740-1793) worked at the mines in Freiberg, and was noted for the acccuracy of his experimental work. Wenz¢l is often given more credit for discovery than he is entitled to, a6 because later commentators have read into his work more than Wenzel had himself seen, and some of the credit must be shifted to JergTnias Benjamin Richter (17621831), who recognized the law of neutrality and established the principles of stoichiometry. However, Richter was unfortunately not an especially competent analyst, and many of his basic data were incorrect. It was Ernst Gotffried Fischer (1754-1831) who rationalized Richter's results and published the first table of equivalent weights; some of the values were surprisingly: accurate. 3~ It was Richter's work which led Berzelius to his atomic weight determinations. 3s The next important figure on the scene wa~'Martin Heinrich Klaproth (1743-1817), who inherited Valentin Rose's pharmacy in Berlin when Rose died four weeks after Klaproth started work there. He later married a niece of Marggraf and bought a lab.oratory with her dowry. He was a very accurate analyst, and very pragmatic in outlook. He discovered uranium, zirconium and cerium and named titanium, strontium and tellurium: Szabadv/try has given an extensive list of Klaproth's contributions to analysis, 39 and pointed out that he was the first to give full procedural details for methods, and a truly quantitative outlook (he sought for the source o'f discrepancies from 100% for a total analysis), and found new elements and investigated the distribution of the elements in natural products, finding potassium in both vegetables and minerals, for example. He also originated alkaline fusion (with potassium hydroxide in a silver crucible, and used platinum for the sodium carbonate fusions

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devdloped by Marggraf), and went so far as to measure the loss of material from the mortar used for grinding samples and to apply a correction. He also developed the idea of ignition to constant weight. At about this time the first books devoted tO analysis began to appear, the first being by Johan Friedrich G~ttling (1755-1809), 40 followed by that by Wilhelm August Lampadius (1772-1842), Professor at the Mining Academy,4' who gave the first quality control tests for analytical reagents (including distilled water) and noted the green flame of alcohol containing boric acid, This particular series of books culminated in the work by Christian Heinrich Pfaff (1773:-1852) who produced the first comprehensive handbook of analytical chemistry. 42 This was the first of the long series of German texts on analytical chemistry, which were pre-eminent in their field up to the first world war.

THE GOLDEN AGE

The nineteenth century saw the great flowering of analysis in Germany. To a large extent this was a consequence of the rise of the chemical industry and the realization that production and q u e r y control could produce a profit. Scott 1 consider~:~l~at much of the rise of the German chemical industry was due to Mohr's work on titrimetry. The German universities came to be regarded as the research centrcs of Europe, and for British and other graduates a research training in Germany was not unusual. During this period quantitative analysis was firmly established and new techniques were rapidly developed. In gravimetric analysis, Heinrich Rose 0795-1864), who was a grandson of Valentin Rose and whose father was a pupil of Klaproth, made a number of advances. 43 He discovered niobium, was the first to use an acidic fusion for decomposition (with potassium bisulphate), and developed the crucible named after him and used for reduction of oxides to metals by ignition in a reducing atmosphere. He also produced a scheme of qualitative analysis based in part on the use of hydrogen sulphide. His "Handbuch dot analytischen Chemic" was published in 1829, and was still used as a Standard text (the 7th edition appeared in 1871) in the last quarter of the century. The book, though packed with information, and organized element by element, is practically devoid of references to the literature and is difficult to use. It was this difficulty, experienced by beginners, that 'led Carl Remigius Fresenius (1818-1897)44 to develop his own scheme of qualitative analysis, based on his own needs as a student, and (at his professor's suggestion) to write his own text "Anleitung zur qualitativen chemischen Analysen" (1841), which ran to seven editions in 10 years, and had reached its 16th by the time of the author's death. He also established the Fresenius Institute in Wiesbaden, and founded the oldest purely analytical journal, Ze[tschrift fur analytische Chemie, which he edited until his death.

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FERENC SZABADVARYand ROBERT A. CHALMERS

The stage was now set for the appearance of Mohr. Up to this time the home of titrimetric analysis was France, where most of the techniques and methods had been developed, and the few German research workers in the field had mainly studied the science in French laboratories. The advantages of the technique were fairly obvious, however, and once interest had been aroused, action followed. Margueritte's permanganate titration of ferrous iron 45 had appeared in 1846, and was soon used in a number of indirect determinations, including the chromate titration developed by Schwarz. 46 When direct titration of chromate was developed by Schabus 4~ and by Penny 4s (independently), the need for an external indicator led to criticism by Schwarz on the grounds of inaccuracy. 49 Karl Leonhard Heinr/ch Schwartz (1820-1890) 5° studied titrimetry in France, and produced the first German textbook on the subject, 21 introducing the term "Massanalyse" into the language. Justus yon Liebig (1803-1873) 51 developed the first complexometric titration s2 (cyanide with silver nitrate) in 1851, and was the first to use mercuric nitrate as a titrant 53 (in 1853). Robert Wilhelm Bunsen (1811-1899) 54 was also active in this field and developed the general technique of iodometry, describing some 18 determinations in a single paper. 55 He used sulphurous acid for titrating the iodine, and this reagent was used long after, although Schwarz introduced thiosulphate as titrant in the same year. 2~ Bunsen is a typical example of the versatility of the great chemists of the time. with wide-ranging interests. His achievements, whether design of simple but extremely useful apparatus such as the Bunsen valve and the Bunsen burner, or more profound such as his work on spectroscopy. was always useful and superbly executed. He was famous for his practical skill and had no sympathy for hypothesis and theorizing. His dictum "Ein Chetalker der kein Physik~r ist, ist gar nichts" sums up his opinion of how a chemist should be trained. He was kind-hearted, with a keen sense of humour, but would not have women students, especially Russian ones. He had to yield once, however, when on behalf of a countrywoman, the Russian mathematician Sonja Kowalewski interceded with him, having left at home the large floppy hat she habitually wore to hide "those marvellous eyes whose eloquence, when she wished it. none could resist". 56 It is also related that a certain student, bringing his attendance card to be signed, said "Behind the pillar. Herr Professor" when asked where he sat in lectures, and that Bunsen replied "So many of you do" but signed the card nevertheless, s Amongst other techniques developed then and still in use, the stannous chloride/mercuric chloride method for reduction of ferric iron ss [Friedrich Christian Kessler ~1824-1896)] s may be mentioned. and the Zimmermann-Reinhardt reagent s9 [Julius Clemens Zimmcrmann (1856-1885) and C. Reinhardq. Jacob Voihard (1834-1910) is now remem-

bered more for his argentometric back-titration method o° (also discovered independently by Charpentier four years earlier6') than the determination of manganese 62 that is also namedafter him. Later in the century, Hans Heinrich Landor (1831-1910) whose name is perpetuated in the Landor reaction and the Landoit-B/Srnstein Tables, suggested gravimetric determinations by bromination of certain organic compounds, b a a n d this was developed into a titrimetric method by Koppeschaar. 64 Hiib165 developed the first method for iodine number determinations, but bromine numbers had been used much earlier66 [August Wilhelm Knop (1817-1891)]. Lange was using eerie sulphate as titrant as early as 1861,67 but the lack of redox indicators was a handicap. Acid-base indicators had been discovered early on, of course, and Caspar Neumann (1683-1737) may be credited with realizing the possibility of end-point detection. Kriiger made the first use of a fluorescent indicator (fluorescein) but it was overshadowed by the rapid introduction of phenolphthalein (E. Luck), 7° Tropaeolin (M. Miller) 7j and Methyl Orange [Georg Lunge (1839-1923)]. 72 Lunge is, of course, also well known for his work on gas analysis. At this stage the great theorists began to emerge, and Wilhelm Ostwald (1853-1932) in "Die wissenschaftlichen Grundlagen der Analytischen ChemiC' gave his theory of indicator action, Which in turn led to Hans Wilhelm Friedenthai (! 870-1943) developing colorimetric determination of hydrogen-ion concentration, 7a with the aid of buffers (suggested by the Hungarian chemist Szily). Although the most exciting developments appeared in titrimetry, several workers were active in other fields. In organic analysis, for example, Johann Wolfgan D/Sbereiner (1780-1849), better known for his "triads", had designed a simple combustion apparatus, 7't and Justus yon Liebig had developed his method for carbon and hydrogen determination, *S which later greatly benefited from Bunsen's invention of his gas-burner. The Dumas method for nitrogen was difficult to use until the nitrometer was invented; the first useful one was due to Schiff in 1868, 76 but meanwhile Franz Varrentrapp (1815-1877) and Heinrich Will (18121890) had produced their method ~ based on production of ammonia by ignition of the sample with barium hydroxide, which was modified by P~ligot t° and swept the field until it was superseded by the Kjeldahl method. Even August Kekul6 (1829-1896) ventured into analysis, and developed a method for halogens in organic compounds, ~s but it was not universally applicable, and Georg Ludwig Carius (1829-1875) developed his well-known sealed-tube method for determining sulphur as well as halogens. 79

Physical methods During this period of highly productive expior-

Carl Friedrich Mohr ation, physical methods of analysis also began to be developed, In some respects they were before their time, because although the principles were established, the requisite apparatus for their application could not be devised. Atomic-absorption spectrophotometry is perhaps the best known example. Optical methods. In the 18th century the difference in flame coiour caused by sodium and potassium had been noted by Marggraf, s° and Johann Wilhelm Rib ter (1776-1810) discovered ultraviolet radiation and noted its effect on silver chloride, st Josef Fraunhofer (1787-t826) rediscovered Wollaston's "black lines" and catalogued them s° and laid the foundations of absorption spectrometry, s2 Julius Pliicker (18011868) showed that the discharge spectrum was characteristic of a gas, s3 and Johann Wilhelm Hittoff {1824-1914) established the existence of line and band spectra, s4 The culmination of the early work was the development of spectrum analysis by Gustav Kirchhoff(1824-1887) and Bunsen ss which almost at once resulted in the discovery of rubidium and caesium, s6 Kirchhoff also reported line-reversal,sT Bunsen, who as already said is one of the outstanding analytical chemists of all time, was the inventor of many pieces of apparatus named after him s8 (including the waterpump, s9 the carbon-zinc battery 9° and the wax-spot photometerg~), and besides working on spectrometry was also associated with iodometry, ss gas analysis,92 electrochemistry, and other topics. However, the early work was purely qualitative, and as late as 1910 Heinrich Kayser (1853-1940) held that quantitative spectrum analysis was impracticable,93 only to be proved wrong by Walter Gerlach with his method of linepairs. 94 Coiorimetry was developed empirically from about 1840, by Lampadius 9s and Carl Heine, 96 and the first colorimeter9~ was designed by Alexander Miiller 0828-1906). The theoretical basis of spectrophotomerry (the Lambert-Beer law) was laid by the work of Johann Heinrich Lambert (1728-1777) who recognized the relation between absorption and the number and size of the absorbing centres in unit volume,9s and of August Beer 0825-1863) who established the relation between absorption and concentration. 99 (It should be noted that these relationships were also discovered independently by Bouguer and Bernard. t°° ) It was Bunsen and Roscoe who introduced the idea of an absorption coefficientt°t and Bahr and Bunsen who first used absorption spectroscopy quantitatively. ~92 The founder of modern spectrophotometry, however, was Carl Vierordt (1818-1884) who realized how the Lambert-Beer law and Bunsen-Roscoe absorption coefficient could be used, and published a table of absorbance-transmittance values. ~°3 The first comprehensive account was given in the book 1°4 by Gerhard Kriiss (1859-1895), the founder of Zeitschrift fur anoroanische Chemic. The use of photo-cells for detection was initiated by Wilhelm Berg. ~°s The firm of Carl Zeiss, Jena, is world-famous for its optical equipment.

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Electrochemical methods. The hydrogen electrode was devised in 1893 by M a x l e Blanc ~°6 (1865-1943) and was used by Wilhelm B~ttger (1871-1949) for the first potentiometric acid-base titration ~°~ in 1897: The first potentiometric titration of all, however, was in 1893 by Robert Behrend (1856-1926), who used a mercury electrode and mercury/mercurous nitrate electrode for titration of mercurous nitrate with potassium chloride, bromide or iodide l°s and a silver electrode and silver/silver nitrate reference electrode for titration of iodide with silver nitrate. The basis of the glass "electrode was noted by M. Cremer, ~°9 and Fritz Haber (1868-1934), working with Klemensiewicz, observed that it should be possible to use a glass electrode instead of the hydrogen electrode, t t o The principle of "dead-stop" end-point detection seems to have been discovered by Ernst Salomon in 1897. ~t~ Harber, of course, is one of the greatest German chemists, and his ammonia process a lasting monument (Nobel Prize 1918). Conductometric titration is based on the work of Friedrich Kohlrausch (1840-1910) on conductivity, and the Kohlrausch bridge 11' is still used (though in rather modified form). The first analytical application was by Friedrich Wilhelm Kiister (1861-1917) and Max Griiters, ~t3 and the technique was later used extensively by Gerhart Jander (1892-1961l Electrogravimetry may also be included in this section. C. Luckow can claim ~14 to have discovered the method independently of Wolcott Gibbs. Alexander Classen (1843-1934) worked extensively on the technique, making numerous valuable contributions, including the first book, t~s which came to rank with the works of Fresenius and Mohr. Luckow also used the mercury cathode for electrolytic separations, t~6 Theory of analysis Another rapid development in this period was analytical theory, and the publication of monographs (some of which have already been mentioned). Ludwig Ferdinand Wilhelmy (1812-1864) may be regarded as founding kinetic methods by his work on the inversion of cane sugar, Rudolph Clausius (1822-1888) contributed to the development of thermodynamics (so essential for understanding analytical chemistry), and August Horstmann (1843-1929) made the first chemical applications of thermodynamics Wilhelm Pfeffer (1845-1920) made a semi-permeable membrane and conducted the first osmotic pressure measurements, which later led to van't Hoff's theory. Hittorf and Kohlrausch, with the work on ionic mobility, transport numbers and conductance, established many of the facts later used in the Arrhenius theory and explained by it. Arrhenius's theory also clarified various other aspects of the chemistry of electrolytes in solution and was later itself related by Ostwald to the law of mass action. Ostwald was the first of the great theorists of analytical chemistry, and his book on it has already been mentioned. His contributions to chemistry are much more extensive than

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this, of course, t~7 and his Nobel Prize in t908 was well deserved. His systematic presentation of the physical chemical basis of analytical chemistry set the pattern for future generations of textbooks. Curiously, Ostwald seems to have ignored the value ofredox methods and the Nernst equation in analytical chemistry.t 1B Walther Nernst (1864-1941), another Nobel Prize winner (1920), was in many ways as important a figure as Ostwald in chemistry in Germany. The Nernst equation ~9 is fundamental to redox chemistry, and nowadays to direct potentiometry, and in those contexts perhaps owes as much to Richard Peters. t2° The Nernst distribution law t21 has had equally far-reaching consequences in analytical practice and in technology. A fascinating biography of Nernst has been written by one of his pupils 122 and is equally interesting as an account of the scientific scene in Germany in the last hundred years. Nernst was the subject of many anecdotes. One concerns his retirement, and his abandoning his herd of cows in favour of carp-rearing because the fish were in isothermal equilibrium with their environment, and Nernst did not see why he should pay to increase the heat of the atmosphere/22, ~23 Another refers to his dislike of "named" units, and his proposal (when the Hertz was decided on) that there should be a unit of flow, l litre/sec, t o be called the Falstaff) z* He also said that as the number of 'Miscoverers" of the laws of thermodynamics decreased as the number of the law increased, and he was the sole discoverer of the third law, the fourth law would have no discoverers at all. The early work on determination of hydrogen-ion concentration has already been mentioned, but the importance of pH in chemistry was first thoroughly realized by a biochemist, Leonor Michaelis (18751949). Michadis also made a fundamental contribution to the theory of redox indicators and acid-base indicators.t 2s Organic reagents The late 19th century was the great era of organic chemistry in Germany, and it is not surprising that the use of organic reagents in analysis was realized. Thus Peter Griess 0829-1888) used various amines as reagents for nitrite) ,°' t27 and his method based on the coupling of sulphanilic acid with the diazotization product of ~t-naphthylamine, 127 in the form developed by Ilosvay t28 and now modified because of modern views on carcinogens, is still used, Otto Brunck (1866-1946) first used the organic complex of a metal ion as the final weighing form, with the ~-nitroso-fl-naphthol complex of cobalt in 1907.~29 Oskar Baudisch (1881-1950) introduced the use of cupferron in 1909) a° Wolf Miiller (1874-1941) TM used benzidine for sulphate determination and Max Busch (1865-1941) introduced nitron as a reagent for nitrate, t 32 The correct temperature range for drying or ignit-

ing such precipitates is important, and the thermobalance has played a major part in this field. Some of the first experiments were by Nernst and Ricsenfeld. lag M icroanal ysi s Edgar Hugo Reinisch (1808-1884) was an early worker in the use of microscopy as a means of identification of crystals obtained by evaporation, but considerably more work was done by Karl Haushofer (1839-1895), ~3'* who developed several new techniques, including micro-filtration. A major problem, of course, was provision of a sensitive balance, and again Nemst was first in the field, with a quartz fibre torsion balance) 35 The Kuhlmann and Bunge balances were developed shortly after, and achieved great renown; Sartorius balances were also famous. Pure reagents were also necessary and the firm of Kahlbaum introduced reagents of guaranteed purity in the late 19th century. THE FALLOW YEARS

For various reasons (political, social, economic, the decline of the German chemical industry and the increasing investment in British and American chemical production) the years between 1914 and 1945 saw a somewhat less rapid and exciting advance in analytical chemistry in Germany. There was a period more of consolidation than of innovation, though certain developments must be recorded. Most analytical work was still classical in type, and instrumentation was developed only slowly. Nevertheless, there was an early interest in automation, especially in developmerit of industrial control methods, which led to the surprise expressed by Belcher and Phillips at the extent of automation of organic microanalysis in Gerinan. 136

In the optical methods Eugen Schweitzer (1905-1934) further developed 137 Gerlach's line-pair method, 9'~ and GUnther Scheibe and NeuMiusser! 3s brought in the use of the logarithmic sector. In flame photometry, Wolfgang Schuhknecht used simple eoloured filters instead of a monochromator, t39 In electrochemistry, H. Fritz developed electrography. 1'*° Radiochemistry was in its infancy, and Rudolf Ehrenberg was one of the pioneers of the use of radioactive reagents, 1.~ a field that is still fruitful. Erbacher and Philipp ~*~ introduced the use of radiotracers for examination of efficiency of separation. In separation methods, Richard Kuhn, Nobel Prize winner in 1938, was active in chromatography of carotenoids, ''.3 A. Bahrdt used a zeolite column for ionexchange, ~44 and Gerhard Hesse laid the foundations of modern gas adsorption chromatography, t'*s Meanwhile, steady progress was being made in organic analysis. Walter Hempel (1851-1961), well known for his work on gas-analysis, had tried unsuccessfully to determine oxygen in organic compounds by combustion to carbon dioxide followed by reduc-

Carl Friedrich Mohr tion to carbon monoxide, and it was not until 1939 that Max Schtitze solved the problem, ~'6 by pyrolysis in the presence of carbon in an inert atmosphere, the method being further developed by Wilhelm Zimmermann t'7 and Josef Unterzaucher. ~'s It was also Zimmermann's work on automation of organic analysis that partly inspired Duval's development of thermogravimetric methods. In qualitative analysis Hermann Staudinger (1902-1965; Nobel Prize 1953) investigated functional group reactions and classification of organic substances. Work on organic reagents for inorganic analysis was also steadily developed during this period, notable typical contributions being the introduction of dithizone ~'9 by HeUmut Fischer in 1925, 0xine by Friedrich Hahn and Karl Vieweg ~5o and by Richard Berg TM (who disputed priority) in 1927, and thionalide T M (also by Berg)in 1935. An equally far-reaching discovery was the development of the Karl Fischer reagent t53 in 1935. Around this time the first complexones were developed by I. G. Farbenindustrie, although they were then used only in industrial applications, their analytical use being discovered much later. One interesting but little-known development was the use by Preuss of a carbon tube heated to 16001800° as an auxiliary atomization device in spectrography. ~5" This is clearly a forerunner of the carbon tube techniques developed in the 1960s for atomicabsorption spectroscopy. Analytical research in this period followed the general pattern of chemical research. Whereas in the early 19th century research was centred mainly in the universities, later on industrial research became more important. Indeed the first industrial research laboratory was established by Emmanuel Merck at Darmstadt in 1826. The BASF, Hoechst, and Bayer laboratories were developed later (in the 1860s and 1870s) and by 1910 industry employed more chemists than the universities did. The war, however, caused severe disruption, and the loss of international patent rights cost the German chemical industry its world supremacy. Inflation increased the erosion of research and development, but the chemical industry continued extensive research, and in 1925 I. G. Farbenindustrie A. G. was established and conducted a great deal of pioneering work. Politics entered the scene, however, and both basic and applied research was pursued haphazardly according to the dictates of the moment. There was also considerable loss of scientists by corn, pulsory or "voluntary" removal from their posts, and between 1933 and 1939 the intake of science and t e c h \ nology students to the universities was more than \ halved, and a quarter of t h e total university staffs had been dismissed. German science was at a low ebb. Research continued, of course, in the schools developed by such deeply respected analysts as Wilhelm Geilmann (1891-1967), but political interference left a lasting mark. One of the few benefits was that Haber and Nernst, whose relationship had long been

615

polite but unfriendly, finally became united when Nernst found the policy towards Jews unacceptable, offered Haber his hand, and asked if Haber could find him a post in his institute as he felt he could no longer work in his own. Haber, however, had himself just resigned as Director of the Institute for Physical and Electrochemistry at Berlin-Dahlem, for the same reason. THE RESURGENCE

The post-war years need little description here-their history will be already well known to readers. The second world war had further depleted Germany's scientific strength, few scientists being excused military service, but once the ravages of war had been repaired, German research effort entered a new phase, not so much innovatory in character, but with the main emphasis placed on consolidation and application of the new discoveries made elsewhere. The result has been a steady expansion of research, especially in the Max-Planck Institutes (worthy successors to the Kaiser Wilhelm Institutes) and an impressive body of published work. It is difficult to compile a list of contemporary German contributions to knowledge without fear of making invidious distinctions, but there can be no doubt about the importance of the contributions of Rudolf Bock and Helmut Bode in solvent extraction chemistry, of Heinrich Kaiser and Hermann Specker in spectrography and detection limit criteria, Klaus Doerffel and Giinter Gottschalk in statistics and information theory, Giinter T61g in ultratrace and ultramicroanalysis, Bruno Sansoni and Ewald Blasius in ionexchange and electrophoresis, Kurt Laqua in laser methods, Siegfried Hofmann in surface analysis, Gerhard Ackermann (continuing the Freiberg mining academy tradition) in organic reagents, Gerhard Werner in kinetic methods, Wolfgang Merz in automation of organic analysis, Knut Biichmann in inorganic gas chromatography, Herbert Weisz in trace analysis, Rolf Neeb and Hans-Wolfgang Niirnberg in polarography or Dieter Klockow in environmental analysis, and these are but a few of the names well known in the literature of modern analytical chemistry. In addition, workers such as Fritz Umland have contributed to many fields of analysis. The 'most outstanding contributions are perhaps the M~ssbauer effect and the development of M~ssbaner spectroscopy, the Massmann furnace in atomic-absorption spectrophotometry, and Egon StahFs work in thin-layer chromatography. To sum up this necessarily brief survey, we can see that German resource and inventiveness has been instrumental in furthering the development of analytical chemistry from its earliest years right' up to the present, more vigorously at some times than others, but never stopping completely. There is a long record of both innovation and development, and there has always been close co-operation between academic and industrial research and requirements, and a generally

616

FERENC SZABADVARVand ROnERT A. CHALMERS

sound appreciation of the importance of analytical chemistry, M a n y of the everyday tools of the analyst spring from G e r m a n discoveries, a n d the world owes G e r m a n science a considerable debt.

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