RUDOLF WINDERLICH Oldenburg i. Oldbg., Germany Translated by Ralph E. Oesper
TEE foundations of the wonderful structure of scientific chemistry were laid by the isolation and study of oxvzen and bv the discoverv and develoument of the -~-"-~ law of fixed combining relations. All thbse who took leading parts in these advances and labors merit imperishable fame and continuing gratitude. Nevertheless, one of the most discerning of these builders has been accorded little attention: Carl Friedrich Wenzel has been overshadowed by the deserved fame of J. B. Richter (1762-1807), who in 1792, was the first to recognize the importance of the neutralization law.' Through his excellent analyses and keen reasoning, Wenzel prepared the way for the neutralization law so well that the great authority J. J. Berzelius championed his cause against Richter and de Morveau. In a letter written in French, Berzelius declared to Davy: "Long before these two chemists, M. Wenzel (Lehre von der Verwandschaft, Dresden, 1775) established this exchange of the elements of two salts in a manner infinitely superior to that of the aforementioned chemists. Furthermore, his work is accompanied by such careful analyses that often they are incorrbct by no more than thousandth^."^ This verdict of the upright and clear-thinking critic has been repeatedly attacked; the opinion has been advanced that Berzelius mistakenly mixed up Richter's and Wenzel's studies. As a consequence, Wenzel has been relegated to the background. Not much is known about Wenzel's life. Born in 1740 a t Dresden, the boy a t an early age was put into his father's hook bindery. Anxious to secure an education, he ran away to Hamburg and then to Amsterdam where he studied surgery and pharinacy. He made a voyage to Greenland as ship surgeon, and spent several years more in the Dutch marine service. In 1776 he returned to his native Saxony, and studied chemistry and metallurgy a t Leipzig. His first hook, "Einleitung m r hoheren Chemie," was published a t Leipzig in 1774; i t reflects his reputation as one of the last defenders of alchemy. In 1780 he was appointed chemist and in 1784 was promoted to chief assessor of the Freiberg mines. His paper on the decomposition nf bv reverberation was -- mat,nls -- --..int,n .-..t,h& .-- .- - constituents - -
awarded a prize by the Copenhagen Academy; it appeared in the Proceedings of this body in 1781. Wenzel was called to the famous Meissen porcelain works in 1786. He died a t Freiberg on ~ e b r u a r y26, 1793. His chief work: "Lehre von der Verwandschaft der Korper" (491 pp.) was published a t Dresden in 1777; a second edition was issued in 1782, and a third with notes appeared in 1800, i . e., after his death. This edition, annotated by David Hieronymus Grindel, an apothecary in Riga, was considerably altered and not to advantage. The notes do not say much and some appear silly. The proof of the existence of constant combining ratios runs through this work like a colored thread. In the preface to this "Theory of the Affinity of Bodies" he says: "At first my only intention was to make for my own use a treatise which should contain the order of the ascertained affiities and the circumstances under which they acted, lest I should not be able to remember them. But it occurred to me that others might iind it useful also, if i t were more worked out. For this end, I endeavored to explain the cause of the law of affiity on a good foundation and the circumstances under which the hodies combine as well as the true relation of their weights to each other." He considered the weight relationship of the individual comuonents of decisive value because of his opinion "it is necessary that any possible combination of two hodies always he in the most exact relationship with every other one." In the Appendix, where he discusses "The application of the theory of the affiity of bodies to special cases" he computes "the weights that are necessary and sufficient for the double decomposition of two salts," e. g., "in order to find out how much sugar of lead we must have for a given amount of blue vitriol, it is only necessary to look up the pertinent relationships in the treatise and compare them with each other." Wenzel used the simplest procedures and the most modest equipment but nevertheless obtained results whose high order of excellence is best evidenced by reproducing several characteristic examples. He neutralized-note, he neutralized, and hence the neutralizaCompare DARMSTAEDTER, L., m R. E. OESPER,"Jeremias tion law was running through his mind-various acids Beniamin Richter." J. CHEM.EDUC.,5, 785 (1928); see also "with the two 6re resistant alkaline salts, alkali f i o FRE.&D. I.. "The Study of Chemical Composition," Cambridge, 1904, p&e i73. vegetabili and alkali fix0 minerali" (KzCOa and NazCOa) "Jm. BerseliusBref, utgifnaaf Kungl!' SvenskaVetenskap- and found "that the ratio of quite pure, dry alkaline akademieu genam H. G. SBderbaum. Bd. I, Teil 2, Brefviixling mellan Bemelius och Sir Humphry Davy (1808-1825). salt to the strongest vitriolic acid is quite close to 290a/,:240, or in a half ounce of ignited tartarus Uppsala, 1912, page 39. ~
~
FEBRUARY, 1950
57
vitriolatus (potassium sulfate) there are 1312/6 grains of precipitate to discover how much fatty acid 1s taken of alkali and 108a/sgrains of vitriolic acid". . . "There- up by each metal" (p. 280). "Since 10 grains of silver fore, the ratio of pure, dry mineral alkaline salt to the precipitate contain 76/s grains of actual silver" (p. strongest vitriolic acid is almost as 1902/a:240, or in 251) and "a half-ounce well-dried silver precipitate one half ounce of fused sal mirabile Glauberi (sodium contains 188 grains of silver and 38 grains of fixed sulfate) there are 106'/4 grains of alkali minerale and air" (p. 267), Wenzel had thus found that 240 grains 1333/, grains of vitriolic acid." Theoretically, 240 of silver carbonate contain 188 grains of silver, 38 grains of anhydrous KsSO4 contain 129.7 grains KzO grains COe and 14 grains of "fatty acid," i. e., oxygen. and 110.3 grains So& Hence, Wenzel's error was 1.5 Actually the oxygen content is 13.9 grains. On the per cent. Similarly, 104.8 grains of NazO and 135.2 basis of Wenzel's figures, 10 grains of the first-mengrains of SOs are present in 240 grains of anhydrous tioned silver carbonate contain 75/s grains silver, NaS04. I n this case, his error was somewhat more (38 X 10)/240 = 1.58 grains COI, and the remainder than 1per cent. The ratio KzO:NazO = 2903/7:1902/s amounts to 0.59 grain "fatty acid," i. e., oxygen is very close to the present value. (theoretically 0.58 grain). However, Wenzel did not Wenzel analyzed ammonium sulfate; his result appreciate what he had found, because he designated was only 3 per cent in error. "Accordingly, in one- the oxygen remainder of silver carbonate as "water." half ounce of dry sale ammoniaco Glauberi there are 99 Wenzel could have overthrown the phlogistic theory grains of alkali uolalile and 141 grains of the strongest with these facts. That he did not do so is evidenced by vitriolic acid." Actually, 240 grains of (NH~)~SOILavoisier's words: "in science as in morals it is difficult contain 145.5 grains of SO3. to overcome the prejudices with which one has ordinarIt should be emphasized that Wenzel was really ily been i m b ~ e d . ~ "Lavoisier's merits remain just thinking in terms of oxides of metals and nonmetals what they were even after it is shown that he had even though, as out-and-out phlogistonist, he did not predecessors. The statement by Wilhelm Ostwald know these concepts. He brilliantly handles the proc- that "Lavoisier merely had to turn the stocking of the esses which eventually had to lead the oxygen theory phlogiston theory in order to transform it into the of combustion. In his "Treatise on fixed air and fatty oxidation theoryn4 though dazzlingly simple nevertheacid" (pp. 253-290 of his Lehre), he states: "It has less glosses over the difficulties. Wenzel did not arrive been known for a long time that when metals are cal- a t clarity even though he, in his metaI salt analyses, cined in lire they become very distinctly heavier even related the metal oxides to the acid anhydrides in the though along with the combustible essence, a part of case of the alkali and alkali earth salts, and to the the metallic substance issues as vapor from many of metals themselves in the other salts: "Therefore, in a them. . . . Since the correctness of these findings half-ounce of ignited selenite (C~SOI)there are 96T/s cannot be doubted, it follows that some material which grains of pure calcareous earth and 1431/8 grains of may come from the air or from the fire itself, must com- strongest vitriolic acid," instead of 98.8 CaO and 141.2 bine with the metal calx and cause the increase in its SOa (error 1.3 per cent). Or again, "the ratio of copper weight, because the weight of bodies cannot increase to the strongest vitriolic acid is almost 1912/3:240," without increase of matter. Metals in tightly sealed whereas in modern terms, Cu:SO. = 63.57:80 = vessels do not become heavier when subjected to fire, 190.6:240 (error 0.58 per cent). "In one-half ounce of well-dried horn lead there however; no metal can be calcined without access of air. Since whatever combines with metals during are 1746/n grains of pure lead and 656/11 grains of calcination is not fixed air, it must be a material of strongest muriatic acid." These figures vary from the present values, i. e., 178.7 lead and 61.3 chlorine, another kind. We will call it fatty acid" (p. 275). I t was precisely such trains of thought and experi- by 2.4 per cent. In view of the fact that elementary ments which led Lavoisier to the overthrow of the chlorine was not known a t the time, the result is indeed phlogiston theory. To Wenzel the law of conserva- surprising, especially since lead is not dissolved by tion of mass was a necessary assumption, and he hydrochloric acid. "Weak muriatic acid does not attack reasoned that some material substance was responsible lead a t all, and the stronger acid merely corrodes it. for the augmented weight of calcined metals. I n However, if it previously dissolved in spiritu nitri fact, he cleverly determined the weight of this added (HNOs) or distilled vinegar, it precipitates from the material. From suitable metal salt solutions he pre- solution with muriatic acid in the form of a, white cipitated the normal or basic carbonate, and ignited, in powder. This lead precipitate dissolves in boiling each trial, one-half ounce (240 grains) of the dried water and comes out again in long pointed crystals. precipitate. "In the fire, the precipitated metals then It melts easily in the fire and issues from open vessels lose some of their metallic substance, their fixed air, as a white fume. Chemists have named this white and water. Since the preceding determinations reveal precipitate horn lead." From one-half ounce of lead, how much of the latter two has been taken up by each Wenzel obtained, via the nitrate, 330 grains of lead metal, or how much actual metal, fixed air, and water chloride, i. e., about 8 grains too much. He used the same procedure with silver. "The horn are present in a half-ounce of precipitate, it is only necessary to subtract the weight of the metal from the a LAvorsIEn,A,, c(Tra,t6elementaire," p, calx which remains after the ignition of a half-ounce 4 OSTWALD, W., Z.physikal. Chem., 44,255 (1908).
JOURNAL OF CHEMICAL EDUCATION
58
silver obtained weighed 319 grains, which agrees rather well with the experience of Director Marggraf, if allowance is made for the slight amount of copper in the fine silver." Smce the balances of the time were not of high precision, the result is little short of astounding. For the analysis of copper sulfate cited above, Wenzel employed precipitation reactions which yielded h i , according to modern ideas, the equivalent or atomic weights of iron, copper, and zinc. From 234 grains of crystallized copper vitriol by precipitation with 60.5 grains of zinc. he obtained 61 mains of copper, a n d by means of.551/, grains of iron he precipitated 601/2 grains of "edulcorated" ( i . e., washed) copper. Much better atomic weights can be deduced from Wenzel's synthesis of sulfides. "Into one-half ounce of pure steel filings, which I heated to bright glowing in a covered tared vessel, I threw a whole piece of sulfur, which weighed just as much, and immediately closed the opening of the vessel with its well-fitting cover. After the superfluous sulfur had burned away, I removed the mass from the fire. The steel filings had run together into a dark spongy slag and had retained 135 grains of sulfur." According to modern values, 137.3 grains of sulfur would be bound. On the basis of S = 32, Wenzel's data yield Fe = 56.9 as compared with the present atomic weight Fe = 55.85. The error is 1.5 per cent. The report of a like experiment with copper reads: "The sulfur entirely permeated the copper foils, they were much thicker than before and could be crumbled easily. From the weight of this mass it was found that copper had taken up 61% grains of sulfur." The theoretical increase for one-half ounce of sulfur is 60.4 grains. Using Wenzel's figures, the atomic weight of copper = 62.44 as compared with the present value 63.57 (error = 1.7 per cent). With lead, "it turned out that one-half ounce lead took up 36l/%grains of sulfur." The corresponding atomic weight (S = 32) is Pb = 210.4 as compared with 207.2 (error = 1.54 per cent). "The silver had taken up 35'/e grains of sulfur and was thereby melted into a lead-colored cake. By heating with iron, copper, tin, and lead, the silver was separated from the sulfur and thrown down in its metallic form." Theoretically, 240 grains of silver combine with 35.7 grains of sulfur. The atomic weight of silver computed from Wenzel's data is 108.36. This corresponds to an error of 0.44 per cent, since the accepted modern value is Ag = 107.88. In addition to the examples of fixed proportions selected for presentation here, and which are easily interpreted in modern terms, Richter's neutralization law can also be extracted from Wenzel's findings, even though he himself did not recognize its rigor and significance. Even today, this neutralization law does not appear directly to the reader of Wenzel's book. Walden has assembled, from various places in Wenzel's text, the governing relationships so excellently that the
-
pertinent Section of his book6 will be copied here. " Wenzel also determined quantitatively the amounts of acids necessary to neutralize alkalies and earths. For the saturation ( i . e., neutralization) of 240 grains of each of his strongest mineral acids (sulfuric, hydrochloric, &ric) with the vegetable (KOH) and mineral (NaOH) alkaline salts, Wenzel required the following quantities: HydrcSulfuric chloric acid acid 2908/r 4404/o 190 286
Plant alkali, grains Mineral alkali, grains Plant alkali/mmeral alkali
1.522
Nitric acid 222'/8 1439/m
1.540
Acetic 2414/o 157'/r
1.547 1.534 Average 1.536
Hence, the ratio of the quantities of the two alkalies required to saturate a fixed quantity of aeid i s constant = 1.656, i . e., independent of the nature of the a d s . This constant corresponds practically to the theoretical ratio K20/Na20 = 1.520. In 1820 Berzelius stated that for the oxides the ratio of the equivalents
"
Conversely, the data can be used to calculate the quantities of these acids required to produce the neutral salts from a Gxed quantity (100 parts) of alkali:
-
=
Sulfuric acid
Nitric acid
Hydrcchloric acid
I n other words, if the quantity of the corresponding alkalies remains constant, the ratio of the three acids required for saturation (neutral salt f o m t i o n ) i s constant, indepadent of the nature of the alkali: " Or again, he determined the quantities of metals and calcareous earth (lime) required for saturating (normal salt formation) 240 parts of each of the acids. For example: 940 parts ofi Hydrochloric acid
Zinc -
Ratio Nitric acid Ratio
Copper
Iron
Lime
273
253'/s
231s//i
3256/g -
1.19 206 1.08
-
-
-
-
1 .08 1.09 1914/~ 175 1.10
1.08
For the two different acids, the ratio of the quantities of metal and lime dissolved (in the saturation of a constant quantity of acid) is once more sufficiently constant." 6 WALDEN,PAUL, " M m , Zahl und Gewicht in der Chemie der Vergangenheit." Stuttgart, 1931, pp. 88-91.
FEBRUARY, 1950
Though Wenzel's main work bears the title, which in English reads "The Doctrine of the A5nity of Bodies," it deals primarily with chemical proportions. Nonetheless, the title is justified because Wenzel attempted to determine quantitatively the chemical affinity by measuring the reaction velocities. He proceeds from the idea "that the more rapidly the common solvent combines with a body, the greater must be the degree of combination, and from this arises the law: The affinity of bodies with a common solvent is in the inverse ratio of the time taken to dissolve." He noted that the trials must be made under identical conditions if the results were to be comparable. "Care mnst be exercised that the solvent is of the same strength and acts a t some fixed degree of heat for like times on equal surfaces." To achieve this identity of conditions, he suggests: "From purest copper, silver, lead, and the other metals, have small cylinders turned which have exactly equal heights and bases, record the weight of each one, and coat a11 of them with molten amber or some other solid lacquer, so that each has only one exposed base on which the common solvent can act. As many equal portions of the solvent are weighed out as one has cylindrical vessels, and all of these small vessels are placed in a large one, which is filled with water in order that all can be constantly kept a t the same degree of heat. Then the cylinders are placed in the small vessels and a11 are exposed to the solvent for some chosen period which mnst be carefully measured with a good timepiece but none longer than the others" . . "and after the solution, the remaining part of the cylinder is freed of the coating and weighed" "Since mercury is a liquid metal, it can be poured into a hollow cylinder cast from sulfur, and for this purpose it is then as well fitted as though it were a cylinder coated with a lacquer. Furthermore, it will be discovered that the times of dissolution under the aforesaid conditions also differ markedly for metals and earths thrown down by alkali." On the basis of the insight gained into affinity and chemical proportions, Wensel, at the end of his book (pp. 447484) gives examples of the "application of the doctrine of affinity of bodies to special cases." He opens with the statement: "In chemistry, as in all other sciences pertaining to the study of nature, the main objective is to discover, by the comparison of the single recognized truths and their combination, still other tmths, which the mind cannot grasp immediately at the first glance."
.
. . ..
Among the problems which Wenzel brought forward as evidence, one has become important to a modern large-scale technical process, namely, the reaction of gypsum with ammonium carbonate.' Wensel rea-
soned: "Next to the two fire-resistant alkaline salts, the volatile alkali has the greatest affinity for vitriolic acid. Consequently, it will decompose alum, the vitriols, Epsom salt, and also gypsum, or what amounts t o the same thing, the volatile alkaline salt will combine with the vitriolic acid of these materials and throw down the earths or metals that were formerly dissolved in it (the acid). However, gypsum is the cheapest of the compounds under consideration, and a t the same time it contains the most vitriolic acid, and so it is excellently suited to our purpose. Hence, Glauber sal amnaoniuc is obtained when enough'of a water solution of volatile alkali to saturate the vitriolic acid is poured on to powdered gypsum." I n modern terms:
+
-
+
GaSO, (NH,)&08 CaCOs (N&)&O, Gypsum volatile alkaline salt + Glauber sal ammoniac
+
The laudatory opinion of Carl Friedrich Wenzel by the great master Berzelius turns out to be well justified after all. D. R. P. 398,491 issued to Badische Anilin and Soda Fabrik.
