INVESTIGATION OF ANTIQUITIES' EARLE R. CALEY The Ohio State University, Columbus, Ohio
MARTIN HEINRICHKLAPROTH(1743-1817)
is well known for his important contributions to chemistry, especially to analytical chemistry and to mineralogical chemistry, but his pioneer work on the chemical investigation of antiquities does not appear to have been much noticed, there being, indeed, no mention of it in any of the general treatises on the history of chemistry. Though a few sporadic attempts to investigate ancient objects or materials by chemical means had been made before the time of Klaproth, these attempts were for the most part futile, largely because no suitable experimental methods were then available. But Klaproth, by means of experimental methods which he, himself, either originated or greatly improved, did accomplish significant work in his investigation of the composition of a considerable number of ancient objects and materials. The results of these researches were ~ublishedin a dozen scattered papers, and in a collected form in the sixth and concluding volume of his L'Contributionsto the Chemical Knowledge of hfineral Suhstances."2 The first paper by Klaproth on the chemical investigation of antiquities, entitled "MBmoire de numismatique docimastique," was r e d before the Royal Academy of Sciences and Belles-Lettres of Berlin on July 9, 1895, and published in the volume of memoirs of that learned body issued in 1798.8 As the title in&cates, this paper deals with the problem of determining the composition of coins, hut the coins selected for esperimental study were in fact all ancient coins, and all ,Irere composed either of copper or of alloys of copper. IClaproth examined six Greek coins and nine Roman coins, found qualitatively what the principal component metals were, and then estimated their proportions, To appreciate the full significance of these analyses as a contribution to chemical research it is important to realize that no one had ever before devised a feasible quantitative scheme for the analysis of any copper allov. Thus Klanroth had before him a t the outspt, .. of . Presented hefore the Division of History of Chemistry a t the 113th meeting of the American Chemical Society in Chicago, dnril 10-97 OAR -" --, >">-.
"BeitrBge aur ohemischen Kenntniss der Mineralktirper," Berlin und Stettin, 1795-1815. a Mbwwires de l'acadbmie royele des sciaoes st belles-lettrea, Berlin, Classe de philosophie ezpbrimentale, 1798, 97-113. A German version of this same paper was later published in Sammlung der deulscha Abhandlungen welche in der kenigliche Akademie der Wissenschaften zu Bwlin ~orgdeseenwmdm in den J d r e n 17921797, Ezperirnenlal2hilosophie. 1799, 3-14, under the title, "Beitrag zur numismatisohe Docimrtsie," and still later under the same title there appeared a modified German version in Allgemeines Journal der Chemie, 6,227-244 (1801).
this investigation not only the task of determining the composition of the ancient alloys but also the task of devising means of doing so. AS might well be expected, the first quantitative scheme for the analysis of copper alloys mas relatively in the light of present standards and was not capable of yielding very accurate results. After the como~ionproducts had been removed from the surface of the metal to be analyzed, a weighed sample was treated with "moderately concentrated" nitric acid, and the reaction mixture was allowed to stand overnight without application of heat. On the next day the Supernatant liquid was poured off and saved, and any undissolved metal or insoluble residue again treated with nitric acid in the same way. If tin was present as shown by the continued presence of a residue insoluble in nitric acid, this was collected on filter paper. Apparently this residue was not ignited but simply dried in an oven a t a low temperature and weighed. In order 60 estimate the proportion of tin in the dried residue, a parallel control experiment was made with a known might of pure tin. It was found from this that 100 parts of dried residue contained 71 parts of metallic tin, *in other words the gravimetric factor was 0.71. If the midue had been dried in such a way that i t was converted to metastannic acid of theoretical composition then the factor should have been 0.7035, which is fairly close to the empirical factor used by Klaproth. By contrast, the present factor for converting the weight of ignited stannic oxide into weight of tin is 0.7877. As a check on the correctness of his results, Klaproth, in Some experiments, dissolved the dried residue in concentrated hydrochloric acid, diluted the solution, and introduced into it a zinc plate. The tin dispIaced by the zinc was then collected and weighed. In other experiments where the dried precipitate was not entirely soluble in the acid, the precipitate was treated with dry reducing agents in a crucible and the resultinp metallic tin was weighed. In none of the determinations was gold observed in the remaining after treatment with nitric acid. The filtrate from the separation of the tin was tested for silver by the addition of a saturated solution of sodium chloride to one portion and the introduction of a weighed copper plate into another. Silver was found to be present in only a single coin. Lead mas separated as sulfate from the solutions from the preceding determinations by the addition of a saturated solution of sodium sulfate followed by evaporation to small volume. The separated lead sulfate
MAY, 1949
was collected and either weighed as such or reduced to metallic lead in a crucible for direct weighing as metal. By means of parallel control experiment it was found that 100 parts of lead sulfate yielded 70 parts of metal, thus giving a factor of 0.70. The present gravimetric factor is 0.6832. The method employed by Klaproth for the detection or determination of iron in the coins was unsound. He believed that the iron was precipitated along with the lead sulfate. Consequently, he dissolved the lead sulfate in hydrochloric acid and tested the solution for the presence of iron with ammonium hydroxide solution or with potassium ferrocyanide solution. Iron was found present, and its proportion estimated, in only two of the coins, though in all probability i t was present in all of them. Needless to say, his two quantitative figures for iron must be considered erroneous. In the Greek coins only copper remained to be determined. This was precipitated as metal from the filtrate from the lead separation by placing i t in a clean iron plate. The precipitated copper was then collected, dried, and weighed. Xlaproth observed that the Roman coins he had for analysis were of two distinct kinds. One was composed of a red metal which he found qualitatively to be copper without any noticeable proportion of alloy. He did not analyze such coins quantitatively for impurities, and he consequently considered them to consist of pure copper. Later analyses of similar coins have shown that they often contain over 98%, and sometimes over 99% copper. The other kind was composed of a yellow metal consisting chiefly of copper and zinc. For the quantitative analysis of these brass coins he divided the filtrate, from the separation of any tin that might he present, into two equal parts. In the one half the copper and any lead that might be present were separated and determined by the procedure described above. The other half served for the determination of the zinc. After trial experiments with four different possible procedures, the following one was adopted for the actual determinations. A thin lead plate was placed in the diluted solution to precipitate all the copper, a process for which several days was allowed. After decantation or filtration, the solution was evaporated to small volume and treated with a saturated solntion of sodium sulfate to remove the lead. The filtrate from this separation was then treated with potassium carbonate solution to precipitate the zinc as carbonate, which was either dried and weighed as such, or ignited to oxide for weighing. The second method of weighing the zinc was better, of course, since zinc carbonate varies considerably in composition in accordance with. the conditions of precipitation and drying. By a pardlel control experiment i t was found that 175 parts of the dried precipitate or 133 parts of the ignited precipitate contained 100 parts of zinc. The corresponding gravimetric factors were, therefore, 0.70 and 0.81, respectively. The present gravimetric factor for converting weight of zinc oxide to weight of zinc is 0.8034. Klaproth expressed the results of these first analyses
243
of ancient copper alloys in terms of actual weight of component metals present in the weighed coin taken for analysis. Thus for a Greek bronze coin of Syracuse, struck in the third century B.C., his results are given as follows: Copper .........................
Lead ........................... Tin ............................ Iron ........................... Total ........................
Grains 233 20 13
1
267
These results converted to percentages are shown in the first column of Table 1. In the second column of this table appear the results of an analysis made by the writer4 of a coin of Syracuse struck at the end of the fourth or the beginning of the third century. Table 1 Analysis by Klaproth of a Greek Bronze Coin of Syracuse end a Recent Analysis of a Coin from t h e S a m e Locality Klapmth's analysis, Element
%
Recent
analysis,
%
Copper Lead Tin Iron Kickel Arsenic Sulfur
A strict critical comparison of the two analyses in Table 1 is not possible because the two coins differ in date of issue, hut from these two analyses and from what is known in general about the composition of Greek bronze coins, certain conclusions may justifiably be drawn. Klaproth was correct in a qualitativesensein finding that copper, lead, and tin were the principal components of a Greek bronze coin struck a t Syracuse in the third century B.C. He was probably not far wrong in a quantitative sense, since, from what is now known ahout the variation in composition of Greek coinage bronze with time, it should be expected that the coin he analyzed would contain a lower proportiou of tin and a higher proportion of lead than the one analyzed by the writer. Klaproth found copper, lead, and tin to be the principal components of the other Greek bronze coins he analyzed, from which he concluded that Greek bronze coins in general mere composed of these three metals. This general conclusion is not correct, because in certain of the earliest coins of various localities only copper and tin are principal components of the coinage bronze. However, his general conclusion does hold for the great majority of the types of these coins. As regards the minor components of Greek coinage bronze, Klaproth was also in error, since, as illustrated by the above analyses, he failed to find most "'The Composition of Ancient Greek Bronze Coins," The American Philosophical Society, Philadelphia, 1939, p. 76.
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JOURNAL OF CHEMICAL EDUCATION
of them, and probably obtained an incorrect result for the only one he did find. Similarly, for a Roman brass coin of the time of Claudins (41-54 A.D.) Klaproth expressed the results of his analysis'as follows: Copper .......................... Zinc ...........................
Grains 296 84
Total ........................
380
-
These results converted to percentages appear in the first column of Table 2, and in the second column of this table appears an analysis by Bibras of a coin of the same ruler, same period, and same denomination. Analysis by Klaproth of a Roman Coin Struck a t the Time of Claudius and a Later Analysis of a Similar Coin Klaproth's analysis, Element Copper zinc Tin Lead Iron Nickel Antimony Suliur
%
Later analysis,
%
77.9 22.1
77.44 21.50
inn n
Trace 0.32 0.24 0.20 Trace 1w.w
ignited to stannic oxide. In the filtrate from the separation of the tin, the test for silver was made with hydrochloric acid instead of with sodium chloride. Lead was separated as before by precipitation with sodium sulfate, but it is noted that the precipitate was well dried by heat. Instead of the factor 0.70, Klaproth now used the factor 0.69 which is decidedly nearer to the present gravimetric factor of 0.6832. He tested the filtrate from the lead separation not only for copper and zinc but also for iron and nickel. However, only copper was found, and this he apparently determined by difference. The results of his analysis of the ancient coin are shown in Table 3, both as he expressed them and as calculated to a percentage basis. Table 3 Analysis of a n Ancient Chinese Coin Metal
As g i v a b?/ Klaproth, Grains
Corresponding percentages
Copper Lead Tin
.17'/4 15'/& 8
67.2 21.5 11.3
U.3U
The agreement of the percentages of the main components in the two analyses shown in Table 2 is remarkably good, and indicates that the results of Klaproth for the copper and zinc content of the coin he analyzed are probably not far from the truth. As with the Greek coins, he failed to recognize the presence of various minor components or impurities that must have been present and therefore made no attempt a t their quantitative determination. However, from his analyses of typical Roman coins he did first establish the most essential fact; namely, that the Roman coins of the first century or so of the empire were struck in brass or copper, but not in bronze. Several years after his investigation of the composition of these Greek and Roman coins, Klaproth8 investigated the composition of two old Chinese coins. From the descriptions he gives, one of these undoubtedly was of considerable antiquity, the other more recent. Both these coins, like the Greek bronze coins he analyzed, were found to be composed of copper, lead, and tin. However, in his analysis of these coins he introduced certain improvements over the procedure he used for the analysis of the Greek coins. The sample was dissolved in nitric acid as before, but the tin was separated by digestion in hot solution. Also the hydrated tin oxide was washed, and was dried and 5 "Die Bronzen und Kupferlegierungen der alten und altesten Volker," Erlangen, 1869, pp. 52-53. 0 "Untersuehung chinesischer Miinzen" in Journal fur die C h a i e , Phrlsik und Mineralogie, 4, 449-451 (1807).
Because of the uncertainty as to the date of this coin there is no point in making a critical comparison from a quantitative viewpoint of the results of his analysis with those of recent analyses-of Chinese coins. However, it is known that certain very ancient Chinese coins contain copper, lead, and tin in similar proportions as principal components. Only in later coins does zinc appear as a main component of the alloy. Klaproth was not only the first to analyze an ancient Chinese coin, but in doing so he was also the first to analyze any ancient object from the Far East. Apparently the last work by Klaproth on the composition of ancient objects was also on coins. In this investigation he determined the composition of a number of Roman silver coins which ranged in date from near the end of the first century A.D. to well past the middle of the third century A.D. An account of a t least part of this work was read before the Academy of Sciences and Belles-Lettres of Berlin on March 19, 1807, but his results did not appear in printed form until considerably later.' This work revealed further improvements on the methods devised by Klaproth for the quantitative analysis of alloys. For example, in some of these analyses, instead of separating the copper as metal for weighing by precipitation with an iron plate, or merely determining it by difference, he precipitated it with sodium hydroxide solution and weighed it as cupric oxide after ignition. His data indicate that the factor "Beitrag zur numismatischen Dokimsie" in Journal fur die Chemie, Physik und Mineralogie, 9,652-665 (1810), and a French version of the same paper, "M6moire sur la docimaaie des m6dailles" in Ann. chirn., 81, 82-97 (1812). In the sixth volume of his "Beitrage aur chemisehen Kenntniss der Mineralkorper," p p 4460, five additional analyses are given which do not appear in either of these pepera.
MAY, 1949
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he used for converting the weight of cupric oxide.into Of metal objects.other than coins, Klaproth first weight of copper was 0.78 as contrasted with the present investigated the composition of the metal of an ancient gravimetric factor 0.7989. His factor for converting mirror, evidently Greek or Etruscan, found in a tomb the weight of dried silver chloride into weight of silver, a t Naples, Italy. His results were first made known indicated for the first time by data given in this pub- in a paper read November 16, 1797, before the Royal lished work, was also somewhat in error. His data Academy of Science a t Berlin.lo His method of analyshow that he considered silver chloride to contain sis was essentially the same as the one he employed in exactly three-fourths of its weight of silver, thus giving his investigation of the composition of Greek bronze a factor of 0.75 as contrasted with the present factor coins, and he likewise expressed his results in grains, of 0.7526. but since he took an original sample that weighed 100 grains, his results in grains for the individual components of the alloy are numerically equal to percentTable .--.4 . ages. These results are shown in the first column of Analysis by Klaproth of Two Roman Silver Coins of Antoninus Pius Table 6. Metal Silver Copper Gold Lead
maw
Coin B, oratm
34.5 5 Trsce Trace
36.7 8.5 0.1 0.2
Coin,A,
Table 6 Analysis by Klaproth of the Metal from a n Ancient Mirror and a Later Analysis by Bibra of the Metal of a q Ancient Roman Mirmr Rlamnt
Klep~oth's analysis, 0/,
Bibra's analysis, %
As an example of his work on the composition of Roman silver coins there are shown in Table 4 analyses of two coins of Antoninus Pius (138-161 ~ . n . )in the form in which Klaproth published them. In Table 5 are shown these same analyses converted to a percentage basis, and also, for purposes of camparison, two later analyses by Bibran of coins of the same denomination struck under the same ruler.
It is not possible to compare directly his analytical results with any more recent analytical results on an object of the same provenance, as apparently no such object has been analyzed since the time of Klaproth. Table 5 Analysis of Table 4 Caleulated to a Percentage Basis and However, Bibra" analyzed the metal from a Roman Two Later Analyses of Similar Coins mirror and obtained similar results for the main components, as is shown in the second column of Table 6, Klaproth's Later analvses. % Metal analvsk. 7% and a few other ancient mirrors have been analvzed A - "B C D with similar results as to general composition. It seems Silver 87.3 80.7 93.28 76.73 likely, therefore, that Klaproth was not far wrong in 6.35 Copper 12.7 18.7 his results for the main components of the metal of Gold Trace 0.2 0.17 this ancient mirror. As with most of his other analyLead Trace 0.4 Trace 2.17 Iran ... ... 0.20 0.12 ses of metal antiquities, he failed to detect and deterNickel . .. ... Trace None mine the various minor components or impurities that 1rr.J.O 100.0 1 0 0 . ~ 1110.00 in all probability were present. He did first establish the essential fact that the so-called speculum metal was not a modern discovery or invention but had been There is nothing significant in the differences in the known and used for mirrors in ancient times. ranges of the percentages of silver and copper in these Later, Klaproth made similar approximate analyses two sets of analyses, since i t is known that the fineness of a miscellaneous variety of prehistoric and historic of the coins of this particular ruler varies widely.' It metal objects from excavation^.'^ The results of these will be seen that Klaproth identified correctly and determined approximately two of the impurities oom"First published under the title, "Analyse cbimique de la monly found in such coins, though he also ignored two masse m4tallique d'un miroir antique," in Mbmoires de l'acadkmie others. On the whole, however, these analyses of royale des sciences et belles-lettres, Classe de philosophie ezpm'menRoman silver coins, apparently the last work on the (ale, 1800, 14-22. A German version was later published in Allg d n e s Journal der Chemie, 6, 245-255 (1801) under the title, composition of antiquities done by Xlaproth, is also "Chemisohe Untersuchung der Metallmasse eines antiken Spie the best from the analytical standpoint. eels."
:
-
-
"Ueber d t e Eisen- und Silher-Funde," Niirnberg and Leip aig, 1873, p. 37. 0 Hammer. "Der Feingehalt der grieohischen und riimischen Miinzen," Dissertation, Tiibingen, 1906, pp. 98-99.
"Die Branzen und Kupferlegierungen der alten und &&en Valker," Erlrtngen, 1869, pp. 70-71. 1' "Chemische Untersuchung der MeWlmasse antiken eherner W d e n und Ger%thehe" in Journalfiir die C h a i e , Physik und Mineralogie. 4 , 351-363 (1807).
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JOURNAL OF CHEMICAL EDUCATION
analyses are shown in Tablc 7. h comparison of these with the numerous later analyses that have been made
as the first chemical analyses of ancient glass but as the first chemical analyses of glass of any kind. h r t h e r more, these first analyses of artificial silicates are of importance from the viewpoint of the history of the Table 7 development of methods for the analysis of silicate Analysis of Various Prehistoric and Historic Metal Obiectlr from Excavations rocks and minerals, since the analytical scheme devised Tin, by Klaproth for the analysis of these glasses set a genPeriod Description % eral pattern for later schemes used for the quantitative Sword Germany Prehistoric 89 11 analysis of such materials. Klaproth first reported the Knifc Germany Prehistoric 85 15 results of his analyses of these glasses in a paper read Knife German" Prehistoric 87 13 before the Royal Academy of Sciences and BellesFragment of armor or fibula. Sicily Greek 89 I1 Lettres of Berlin on October 4, 1798.14 Fragment of dish Italy Greek 86 14 All three glasses analyzed by Klaproth were highly Metal from Quadcolored and opaque, one being bright red, one brilliant wa Island of 99 3 0.7 Chios Greek green, and the other sapphire blue. His main purpose Fragment of ring Germany Roman 91 9 in analyzing them was to determine the cause of the coloration, but in doing so he made essentially complete of similar objects indicates that Klaproth was in all analyses. likelihood essentially correct as to the nature and proIn preparing these glasses for analysis, they were portion of the main components of these objects. ground to a very fine powder, and samples of 200 He also investigated the composition of certain metal grains, a very large amount from the standpoint of antiquities of the cathedral church of St. Simon and modern analytical practice, were weighed out. The St. Jude a t Goslar, Germany.13 This church was analysis of the sample of blue glass, for example, was founded in the eleventh century, and it is likely that begun by fusing the powdered sample with twice its most of the objects date from that time, although there weight of sodium hydroxide. Though Klaproth does are some reasons for believing that the altar of this not so state, this fusion was probably done in a silver church was formerly a pagan altar of considerably crucible, as it is known from some of his papers on earlier date. At any rate, it appears reasonably cer- mineral analysis that he customarily used a silver tain that all the objects can be dated within the crucible for such purposes, a refinement that he, himmedieval period in Germany. The method used by self, introduced into analytical practice in place of the Klaproth for the analysis of these objects was essen- former use of iron crucibles. Platinum crucibles were, tially the same as that used for his analyses of Roman of course, not yet available. After cooling, the fused brass coins, though he did employ certain improve- mass was treated first with water, and then with an ments in procedure. The results of his investigation excess of hydrochloric acid. The resulting solution are shown in Table 8. was evaporated to dryness, and after digesting the dried mass with water, the insoluble residue of hydrated silica TABLE 8 was filtered off. This residue was dried, ignited to redAnalyses of Antiquities of the Cathedral Church at Goslar ness, and weighed as silica. An excess of ammonium hydroxide solution was Coppeil., Zinc, Ld, Obiect % % % added to the filtrate from the separation of the silica, ...which resulted in the formation of a bluish solution 69 18 13 Altar Enclosure of altar 75 12.5 12.5 containing a brown precipitate. This brown precipi84 16 Chandelier tate was collected and washed, the filtrate being reImtrerial chair 92.5 6 2:5 served for later separations. The brown precipitate was digested with potassium These analyses are of considerable interest and imhydroxide solution which was found to dissolve a small portance as showing the use of brass in Germany in part of it. The dissolved matter was found to reappear medieval times. In addition, they have a special value again on adding hydrochloric acid to the potassium as the only analyses that have ever been made of objects hydroxide solution, and this mas taken as evidence of of similar provenance. the presence of alumina. To determine it, a hydroApparently the only nonmetallic antiquities anachloric acid solution was prepared from which the lyzed by Klaproth were three specimens of ancient alumina was precipitated with sodium carbonate soluRoman colored glass mosaic from the ruins of the villa tion. and this vrecinitate was washed. ienited to red of Tiberius a t Capri, but his analyses of these glasses " First published under the title, "Sur quelques vitrifications are of considerable importance and interest, not only 'T.Jntersuchung einiger alten Metallmassen aus der Stiftskirche au Goslar," in Journal j w die Chemie, Physik und Mineralogie, 9,401407 (1810). A somewhat abbreviated account appearedin the same year in the old Annales de Chimie, 75,317-321 under the title, "Anslyses de quelques alliages de 1'Eglise de Goslsr." la
antiques," in Mlmoires de l'acadbmie myale des sciences et belleslettres, Berlin, Classe de philosophie ezpe7imatale, 1801, 3-16. A German version of this same paper was later published under the title, "Ueher antike Glmpasten," in Sammlung dm deutschen Abhandlzlngen zuelehe in der kdnigliche Akademie der Wissenschajten zu Bwlin vorgelesen worden in den Jahren 1789-1800, EzperimentaGPhibsophie, 1803, 3140.
MAY, 1949 heat, and weighed as alumina. The undissolved part of the brown precipitate was taken to be iron oxide, and this was washed, ignited to redness, and weighed. The bluish solution from the ammonium hydroxide treatment was concentrated by slow evaporation until the major part of the sodium chloride had crystallized out. The supernatant liquid, which appeared to be somewhat acid, had but a slight green tint. This solution was carefully tested for the presence of cobalt without success, and appeared to contain only copper and "lime." The copper was shown to be present by the formation of a brown precipitate on the addition of potassium ferrocyanide. On separating and weighing this precipitate i t was found to amount to 2 grains, which Klaproth took to be equal to 1 grain of copper oxide, obviously a rough approximation. In the filtrate from the separation of the copper, the calcium was precipitated with sodium carbonate solution, the resulting calcium carbonate being separated, ignited, and weighed to determine the amount of lime. Apparently no lead was present in this blue glass. In the other two glasses it was separated as chloride by evaporating the filtrate from the silica separation to a small volume and adding dilute alcohol to bring about more complete precipitation. For the determination of the lead the crystals of lead chloride were washed with dilute alcohol, dried, and weighed. In the analysis of the red glass, for example, the weight of the lead chloride was found to be 32l/, grains which Klaproth considered, apparently on the basis of some separate experiments, to be equal to 28 grains of ordinary lead oxide. In other words, his factor was 0.86 which is considerably different from the present factor of 0.8025 for this same conversion. The filtrate from the separation of the lead as chloride was then used for the other separations and determinations. The results of his analyses of these three glasses are shown in Table 9. That these results are only approximate is evident both from the imperfect analytical procedures he used and from the results themselves. Since he used only a single evaporation for the separation of the silica, some of this must have gone through and contaminated the precipitate formed by ammonium hydroxide, and caused high results for the alumina or iron oxide, probably both. On the other hand, his results for silica may actually he too high, since he may not have used a sufficiently high temperature for its ignition and he made no corrections for the impurities in the ignited precipitate. Certainly, the silica content of the blue glass seems too high for a glass of this type. Also the calcium oxide content of this blue glass, in particular, seems much too low. It is not unlikely that a considerable proportion of the calcium was precipitated as carbonate and counted as iron by reason of the presence of carbonate in the ammonium hydroxide used as a reagent. Again, it would appear that the reported proportions of lead in the red and green glasses are too high by reason of the use by Klaproth of an incorrect gravimetric factor. Furthermore, Klaproth says nothing about the discrepancy between the
247
amount of sample taken for analysis and the summations of his analyses. At least part of this general discrepancy must have been due to the presence of alkali oxides, and it is curious that Klaproth says nothing about their presence. He could not be expected, of course, to think in terms of determining the proportions of potassium and sodium in these glasses, since these elements had not yet been isolated and recognized as distinct metals, but, in view of the knowledge of glass makilig current in his day, it could be expected that he would have known that alkali metal compounds were essential ingredients in the manufacture of glass, a t least of glass containing little or no lead. Also his analytical figures do not take into consideration the fact that certain of the components could exist in the glasses in different states of oxidation, though he recognized that copper did exist in different states. All these considerations lead to somewhat different figures than he gives for the composition of these glasses. In Table 10 are shown, on a percentage basis, recalculated figures for his analyses that probably represent closer estimates of the actual composition of these Roman glasses than the ones he published. TABLE 9 Analysis by Klaproth of Specimens of Ancient Glass Mosaic Red
Green
Blue
130 15 20 7 11 13 196
163 None 1 19 3 0.5
- -
142 28 15 2 5 3
Silica Oxide of lead Oxide of copper Oxide of iron Alumina Lime
-
Total
195
186.5
TABLE 10 Klaproth's Analyses of Ancient Glasses Recalculated and Ekpressed o n a Percentage Basis Red glass,
Green
Blue
glass, %
glass,
Kone 2.5 1.5 4.3
3.5 5.5 0.5 2.5
None 1.5 0.3 7.7
'z
Comwonent
Ferric oxide Aluminum oxide Calcium oxide Alkali oxides and loss
%
Total -
-
--
He was not far wrong in his conclusions as to the substances responsible for the colors of these glasses. He concluded that copper was the main coloring agent in both the red and green glasses, but that the difference in color was the result of different states of oxidation of the copper. This was an advanced idea for the time (Continued on page 888)
JOURNAL OF CHEMICAL EDUCATION
XLAPROTR AS A PIONEER I N TEE CREMICAL INMSTlGATION OP ANTIQVITIES
(Continued from page g47)
in which he worked. We would say now that in the red compounds were the ingredients that gave these glasses glass the copper was largely or entirely in the cuprous their colors. state, whereas in the green glass it was largely or enThus it is evident that Klaproth did a variety of imtirely in the cupric state. He apparently did not recog- portant pioneer work on the chemical investigation of nize that the iron in the green glass must have oon- antiquities, and that in doing so he made important tributed something toward its color. He concluded original contributions to the art of chemical analysis. that iron was the sole coloring agent in the blue glass, In spite of their approximate nature, some of his but he did not realize that iron also could exist in differ- analyses are still useful today, especially those of ent states of oxidation and that the iron in this glass objects and materials of unusual provenance for which must have been largely in a particular state of oxida- no later analyses exist. Some of his general coution. It is not unlikely, however, that copper in the clusions and interpretations based on hi analyses are cupric state also contributed something toward the still valid today. Not only was Klaproth a pioneer in color of this blue glass, especially in view of the possibil- the chemical investigation of antiquities, but the ity that the reported proportion. of iron may be too amount, variety, and importance of his contributions high. At any rate, he did achieve the main objective exceeded those of any other worker in this field for over of his analyses in that he found that copper or iron half a century.
