The Poisonous Nature of Carbon Dioxide (128 Years Ago!)
Frank L. Pilar University of New Hampshire Durham, 03824
A recent spring cleaning of my attic brought to light a chemistry textbook written in 1847 by J. L. Comstock, M.D., entitled "Elements of Chemistry." A subtitle adds the comment "In which the recent discoveries in the science are included and its doctrines familiarly explained." The publisher was Pratt, Woodford and Co., 159 Pearl Street, in New York City. The book is of small format (about 12 X 19.5 cm) and contains slightly in excess of 425 pages. There is no table of contents, but a very short (and inadequate) index is included. A handwritten notation on the corner of the flyleaf says $1. Judging by the excellent condition of the book, one is tempted to regard this as the original selling price. In any event the book has proven to be a treasure t o read. On the one hand it is startling to read about a topic one might think was a recent discovery (e.g., the platinumcatalyzed decomposition of ethanol vapor), but on the other hand one reads almost with disbelief gross misinformation about the properties of a simple substance such as carbon dioxide. The author states that two sets of symbols are in current use for denoting chemical elements: one set due to Sir Thomas Brande (not illustrated in the text), and another devised by Berzelius (very similar to modern notation). Only the latter symbols are employed by Comstock. Some variations from current usage are PI instead of P b for lead and Z instead of Zn for zinc. The element silicon is called silicium and beryllium is called glucinum or glucinium (symbol G). The two spelling variants appear almost randomly-and without explanation-throughout the text. Comstock states that although there are 54 known elements, i t is likely this number will be reduced when some are found to be compound in nature. The author mentions chemical formulas briefly but prefers not to employ them. He states that it is easier and more accurate to give word descriptions of compounds. For example, water is described as follows: 1eq. Oxygen, 8 1 eq. Hydrogen, 1. This is taken to mean that water contains the proportions of 1 equivalent of oxygen (of atomic weight 8) to 1 equivalent of hydrogen (of atomic weight 1). Nevertheless, Comstock provides a few examples of one way of writing chemical formulas; for example, nitrate of potassia (potassium nitrate) is written K N 6 0 or, preferably, (K + 0 ) (N 5 0 ) . The latter form emphasizes the origin of nitrate of potassia from potassia, K 0 , and nitric acid, N + 5 0. The correspondence to our current notation of KN03 is most easily seen by recalling that early 19th century chemists considered oxygen t o have an atomic 0 correweight eight times that of hydrogen. Thus, K 5 0 to Nz05 (the anhydride of sponds to KzO and N HNOd. Water, of course, was written H 0. Although it had been known for some time that water was formed from two volumes of hydrogen gas and one volume of oxygen gas (both measured a t the same pressure and temperature), Avogadro's assertion (1811) that equal volumes of two different gases a t the same pressure and temperature contained equal numbers of molecules was not known or accepted until Cannizzaro reintroduced the idea at the 1860 Karlsruhe Conference and showed how it could be used to remove ambiguities in atomic weight determinations.
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I t is of interest to note that a precursor of our modem subscript notation (e.g., KNOs or KO, NO5 for potassium nitrate) was introduced as early as 1834 by Liebig and Poggendorff. However, the great chemist Berzelius complained when an editor used the subscript notation in one of his papers. Incidentallv. Comstock deliberatelv rounds off atomic weights as a d a i d to the memory (so d;e claims). For example, the atomic weight of chlorine is listed as 35.42 (the modern value, to the same number of significant figures, is 35.46), but throughout the text a value of 36 is used. There is no hint of the rounding-off criterion which leads to 36 instead of 35. Dalton's atomic theory is mentioned by the author but is regarded as no more than a convenient way of rationalizing the law of definite proportions. Comstock states that the atomic theory, however useful and interesting, can never be proven since the existence of atoms is not demonstrable. I t is a sobering thought to those of us who grew up accepting atoms as reality that their existence was not universally accepted until the early years of the 20th century. As late as 1890 the great German chemist Wilhelm Ostwald only grudgingly admitted the possibility of atoms existing. The turning point came in 1905 when Albert Einstein showed that Brownian motion provides not only relatively direct evidence for the existence of molecules but also a means of counting them. There is some discussion in the text of the systematic naming of compounds, but the stated rules are often honored in their breach. Iron sulfide is called sulphuret of iron, iron carbide is called carburet of iron, and methane is called carburet of hydrogen. What we now call manganese(I1) oxide is called protoxide of manganese, manganese(II1) oxide is called deutoxide of manmnese. and manganese(1V) is called peroxide of kang&ese. 1n general, that oxide with the least number of oxveen atoms ner oxidized atom carried the prefix prot- with highe; oxides being desianated bv the orefixes deut-. trit-. etc. The orefix per- was sometimes (but not consistentl;) used for that oxide with the hiehest known orooortion of oxveen. For ex- . ample, water is referred to as pmtoxide of hydrogen, but what we now call hydrogen peroxide is called deutoxide of hydrogen by Comstock. Throughout the book there are many references to carbonic acid (what we now call carbon dioxide). Carbonic oxide (the modern carbon monoxide) is mentioned very briefly and is said to lack sufficient oxygen to be an acid. Comstock does not appear to be up-to-date in his concept of acids; even prior to 1846, work by Thomas Graham on acids of phosphorus and Liebig and Wahler on ~olvbasic . . organic acids~cleilrlyshowed that replaceable hydrogennot oxygen-was must characteristic of acids. It should also be noted that early chemists commonly employed the term acid for what we now term an acid anhydride. The preparation of C02 by heating of limestone and the acidification of marble are described. Much is made of the highly toxic nature of carbon dioxide whereas carbon monoxide is treated almost in passing with merely a brief note as to its flammability. Initial shock turns to amusement when one reads: "Carbonic acid, although deadly poison
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Volume 52, Number 12, December 1975 / 791
when taken into the lungs, may be taken into the stomach (as carbonated water) not only with impunity hut with pleasure." The author betrays some wonder a t this strange dual hehavior of carhon dioxide and even provides some unconvincing explanations for it. Today, it is not difficult to understand how the confusion between CO and COz arose, even though both gases were known and characterized a t the time. Many of the tests of Con toxicity were carried out on l a b o r a t o ~animals in atmosnheres in which oxygen was removed Gy burning charcoal.'~t is small wonder that the resultine behavior of the animal. described in some detail by ~ o m i t o c k matches , very closely the symptoms we now attribute to carhon monoxide as~hvxiation. .. Evidently, no one thought to repeat the experiment using COz generated from limestone or marble. It is also stranee that no one tested the toxicity of carhon monoxide since% was a common experiment in those days (even a popular parlor trick) to subject birds and mice to any gas the experimenter could acquire a sample of. Had High School Science Fairs been popular in the early 1800's, some student would surely have made the discovery! I t is ironic that the other cited evidence for C02 toxicity contains the same flaw as the animal experiments; for example, Comstock mentions the case of a Parisian family in which five out of seven members succumbed to the fumes from an oven used to heat limestone. In another reference to carhonic acid, Comstock states that plants manufacture oxygen from carhonic acid and do not decompose water. The "prooP' was based on the two facts: (1) vegetables do not emit oxygen unless carbonic acid is present, and (2) if a plant is confined in a mixture of carhonic acid and oxygen (of known amounts), the proportion of oxygen increases as that of carhonic acid diminishes. I t is difficult for today's scientist, to whom the ahove arguments are clearly so inadequate, to understand how Comstock and his contemporaries could have accepted such shoddy reasoning. Today, thanks to modern tracer studies, we know that the oxygen of photosynthesis arises from water. Exothermic and endothermic reactions are discussed in terms of a so-called law of condensation, viz., when bodies pass from a rarer t o a denser state, caloric (heat) is evolved. This law was a generalization of the observation that air becomes warmer when it is suddenly compressed. Thus, the author points out that when iron and sulfur are combined, heat and light are produced, since the product, sulphuret of iron, occupies less space than the free elements. Electrical phenomena are discussed in considerable length as specific examples of the four imponderable agents: light, caloric, electricity and galvanism. Although some similarities between static and galvanic electricity are noted, the two are alleged to he different in several fundamental ways. For example, i t is noted that common electricity (from a statically charged source) produces no heat when moving through a perfect conductor whereas galvanic electricity (produced by a voltic pile) evolves much heat in the same conductor. Comstock discusses the consequences of increasing the number of plates in a voltaic pile and of increasing the size of the plates, but the lack of simplifying concepts such as electrical potential and charge (as intensi-
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Journal of ChemicalEducation
ty and capacity factors of electrical energy) prevented him and his contemporaries from ~ r o d u c i n ea unified theorv of electricity and galvanism. During a discussion of various metals and their properties, directions are given for constructing an aphlogistic or flameless lamp. This is an early adaptation of the platinum-catalyzed decomposition of ethanol vapor; a heated platinum wire is suspended just above the surface of liquid ethanol where i t continues to glow with red heat as long as some liquid alcohol remains. Comstock's explanation of the phenomenon is correct as far as i t goes; the heat emitted by the platinum wire initiates thermal decomposition of the alcohol and this exothermic reaction reheats the wire. I t should he noted that even as early as 1836, Berzelius pointed out the similarities between yeast-induced fermentation of sugar and the decomposition of Hz02 in the presence of metals such as platinum or silver. For such nrocesses he coined the term'catalytic and called the yeast and metals catalysts, substances whose only role was to affect the rate of reaction (a contemporary, Mitscherlich, preferred the term contact substances). However. Berzelins' and Mitscherlich's ideas were not universally accepted until decades of quantitative rate studies clearly revealed the role catalysts (or contact substances) played in many chemical reactions. As an amusing sidelight, Comstock recommends n prnctical use of the flameless lamu: to provide a fast wav of ieniting a match when one needs to light a candle in a hurry. The bottom of each page of the text contains questions (in fine print) for the reader to use in testing himself. Most of the questions require the recalling of facts stated in the page immediately above. Some samples are: What is the difference between a melting pot and a crucible? Is vinegar ever found ready formed in plants? What does crassamentum consist of? (that part of the blood, besides the serum, consisting of fibrin and coloring matter). Do the compounds of oxygen and chlorine possess any value in the arts? (expected response: They are known only to chemists and, with the possible exception of chloric acid, possess no value in the arts). Suppose it is found that 100 cubic inches of oxygen weighs 34 grains, how is its specific gravity found? (Some of todav's teachers mieht want to a .. ~ ~ r.o o r i ate the latter questioi!). In what m a k e r may steel instruments he gilded with an ethereal solution of gold? The author states in the preface that he-has consulted, among others, eminent authorities such as Sir H. Davy, Mr. Faraday, and Dr. Henry and that he has personally verified some of the deductions of others as well as carrying out personal experiments of his own. If the publisher's claims can he believed, the text was widely used in this country and abroad (my copy is a 13th edition). Discounting the interpretations and "facts" which have not survived the tests of time, one can learn more practically useful descriptive chemistry from Comstock's text than from a modern general chemistry text. How many texts of today give the student directions for gilding steel instruments with an ethereal solution of gold? And, as a parting thought, how will some of our 1975 texts strike a reader 128 years from now-in the year 2103?
