The NEED
of
MODERNIZING the GENERAL COURSE* ERNEST A. WTLDMAN Earlham College, Richmond, Indiana
W h y modernize? Because chemistry i s a science as well as a practical art. Because theory has a large place i n a science. Because the theoretical aspect of chemistry is changing rapdly. The modern theories concerning atonzic structure and valence, ionization, and acids, bases, and salts are complementury to each other. The adwantage in teaching that may be derived from considering them as the framework for the course i s discussed and illustrated. Implied changes in terminology are mentioned. The errors in several of the older concepts are referred to and the more satisfactory &ture of the science presented by the newer anes i s emphasized. Particularly important i s the use of new ideas in explaining the oridation-reduction reaction, c o r n p h i o n formation, hydrolysis, the function of hydrated ions. The Aston method of atomic weight determination i s recommended.
consequence, our course must change equally as rapidly. This means more than metely including new data and concepts. Recent progress has been sufficiently comprehensive in implication to require a fundamental revision. Several of the subjects that are to be considered in this symposium may be grouped for the convenience of the present purpose into three main divisions: first, Atomic Structure and Valence; second, Ions; third, Acids, Bases, and Salts. These overlap each other, to be sure, and the consideration of any one topic cannot be complete without dealing with them all. It shall be my purpose to stress this fact. Instances may be found not infrequently in which chemists have been led astray in the appraisal of one of the modern theories because of not taking another into account. For instance, the existence of molecular HClin water solutions is not evidence against the theory of complete ionization of strong electrolytes. It would seem to be so only when one adheres to the older theory of acids: namely, that they ionize into free hydrogen ions or protons and an anion. In the new theory the number of ions in solution is limited by the extent to which the reversible equation:
+ + + + + +
A
T THE outset we may attempt to answer the question, "Why modernize!" The answer has two aspects: first, the general values in doing so; second, the reasons that grow out of the progress of our knowledge of the subject. The first set of reasons is implied by the fact that we .. HX H,O a H,O+ Xare teaching a science, a subject that develops because of the interaction of several kinds of activity, such as is displaced to the right, and this displacement is a induction, deduction, speculation, and experiment. function of concentration. The completely ionized The collection of data followed by the formulation of strong electrolyte is not HC1, but the product of this generalizations and the testing of them by experiment reaction, oxonium chloride. has perhaps sometimes been given too much weight as It is this overlapping and intermeshing bf our subthe essence of the scientific method. Certain19 logical ject matter that, in my opinion, makes necessary a deduction and the speculative use of the imagination complete and fundamental change in our approach to have been a t least equally important. The last has the general chemistry course. And my part in this given us our theories, without which we should have a symposium, as I conceive it, is to attempt to point out practical art only, not a science. In a very real sense in a synthetic manner how these several conceptions science is the making of theories. We cannot, theremay be welded into a reasonably consistent structure fore, teach chemistry truthfully without including that affords the student a much more satisfactory them as the most important part of the course. The picture of our science than he has obtained previously. teacher who would confine himself to factual laboratory It is unthinkable that we should continue to make soobservation is turning his back upon such processes as called revisions by attaching brief descriptions of those that gave us the atomic theory, the structure modern concepts to the framework of the old course. theory of organic chemistry, the theories of atomic That way lies confusion. structure, valence, etc. I anticipate that our efforts in this symposium to atWe come, then, in the second place, to the fact that tain a well-balanced view of the general course may the theories of chemistry are changing rapidly. In even have some effect upon the structure of the science Presented as a contribution ro the Symporium on hlodtrniz- of chemistry itself-may succeed in pointmg out ing thc Courac in Cicncral Ctlmli$try of thc Division of C h e m ~ m l valuable implications to those whose research has been Education a t the 8Arh meerine of the .4 C. S . Cle\rland. Ohio. confined to specific parts of the subject. September 10-14, 1934, and &bsequently revised.
+
11
+
:.
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The remarks that follow do not contain a wellrounded description of the topics mentioned above since that service will be rendered by other speakers more adequately than I could possibly perform it, and I shall try not to infringe unduly upon their domain. But certain phases of their subjects I want to refer to in the interest of clearing the way for the extensive use of the new concepts in the general course. ATOMIC STRUCTURE AND VALENCE
The three most significant accomplishments in the development of chemistry are the atomic theory, the periodic law and classification, and the elucidation of atomic strncture and valence in so far as the latter has been accomplished. The last give more meaning to the periodic law than the nineteenth-century chemists ever dreamed of. None of us would think for a moment of attempting to teach chemistry without a periodic chart. It is now equally futile to attempt it without correlating the properties of the elements with their electronic structures. Of course, I do not mean that we should inflict the mathematics of quantum mechanics upon our students. Mathematics is a concise language, and most of us, teachers as well as students, will never become expert in its use. But we can teach in the language with which we are familiar the pictures that come as near as is reasonably possible to corresponding with the mathematical expressions. There is ample evidence that such pictures are to be regarded as extremely valuable in spite of their non-mathematical character. One has only to remember, for illustration. the extraordinarv science of organic chem" istry. In sixty years organic chemists have by the use of pictures and models of molecules constructed a science that in completeness and consistency is rivaled by the science of numbers alone ( 1 ) . May we now mention briefly some of the topics related to atomic structure which are important as part of the general course. More detailed and specific treatment of them will be presented by later speakers. The Constituents of Atoms. We are no fonger able to teach that atoms are composed of protons and electrons, the total numbers of each being the same as the number of units in the atomic mass ( 2 ) . These appear to be two of the constituents; but neutrons, positrons, and deutons have also been obtained from atomic nuclei recently, and neutrons of mass 2, neutrinos, and negative protons have been suggested. We have heretofore omitted, usually, the alpha particles in listing atomic constituents because we assumed that they were ultimately composed of protons and electrons, but they may instead contain only neutrons and positrons. The proton and the deuton may turn out to be complex, being positron-neutron combinations, the neutron being a non-electrical unit of mass. On the other hand the neutron may be a complex resultingfrom annion of a proton with an electron. Evidence for this view (3) as well as against it (4) has been submitted recently.
It seems that during the last few years we have over-simplified unjustifiably the question of the ultimate constitution of matter and that we should now be more cautious. Our time-honored method of explaining the difference between the isotopes of an element: that is, by a variation in the number of protons and electrons in the nucleus, appears to be obsolete. We may now do this less definitely, but perhaps more truthfully, by stating that the principal difference appears to be due to the different numbers of mass units (perhaps neutrons) in the respective nuclei. At the same time we must remember that the radioactive atoms, at least, and probably others seem to have nuclear electrons. In consequence, a small part of the mass differences may be caused by variations in the numbers of electron-positron pairs. The discovery of deuterium and tritium and the probability that they differ somewhat in chemical properties from protium indicates need of caution in stating that the chemical properties of the isotopes of an element are identical. Anderson (5) suggested in his article describing the discovery of the positron or positive electron that the familiar negative electron be called the "negatron." This name has the advantage of being logically descriptive of the most important property of the unit. Its general adoption is recommended for the sake of making the chemistry course as consistent as possible. This benefit to the student and to our science as well is adequate reason for those of us who have become familiarwith the older usageto discipline ourselves sufficiently to make the change. I have tested myself in my own classes and I have found that it is possible. Furthermore, the members of my general chemistry class were unanimously in favor of using "negatron" a t the end of the past year after they had used it for the first semester and "electron" during the second. Ninety per cent. of the class had previously been familiar with "electron." If I may be permitted, I shall use "negatron" in the remainder of this paper. ' Valence. The negatron theory of valence and the X-ray analysis of crystals promise to place inorganic chemistry upon as systematic a basis as the structure theory has placed organic chemistry. The chief reason for using the negatron theory is that as an extension of the periodic chart based on atomic structure it serves beautifully to elucidate the chemical properties of the elements. The subject thus becomes more of a science and less a craft. The value of the theory is much enhanced by the increasing importance of the theory of complete ionization of strong electrolytes and by its need for the interpretation of the knowledge now available to us because of X-ray crystal analysis. The difference between electrovalence or ionic valence and covalence, which is a reasonably sharp distinction in most compounds (6), should be known as familiarly by our students as the names of the common elements. These terms are preferable to those formerly in use; "polar" and %on-polar," "heteropolar" and "homopolar," on account of the fact that
.
usage has determined that "polar" shall be applied to molecules of substances that have an electric moment. The latter use is the more rational. The word "polar" does not apply properly to the relationship between two separate units such as the sodium ion and the chloride ion unless we are dealing with sodium chloride vapor, which is probably not ionic. Thus the theory of complete ionization requires that we abandon the term "polar" with respect to the valence force between ions. The generous use of the Lewis negatronic formulas is, of course, desirable in representing the mechanisms of reactions. The most important type of reaction in chemistry is oxidation-reduction. Direct union, decomposition, displacement, and substitution all come under this head. (Double decomposition is not a reaction but a misconception.) The oxidation-reduction reaction is particularly well explained by the use of the negatron theory of valence. We have become familiar with the explanation of oxidation as denegatronation and of reduction as negatrouation. When accompanied by models and negatronic formulas the change in the case of elementary atoms and simple ions is much more readily understood than it was when represented by the methods in use twenty years ago. We can go much farther a t present and give a reasonably satisfactory explanation of the change with respect to covalent compounds. This involves the displacement of the bonding negatrons away from the nucleus of the atom oxidized and toward that of the atom reduced. The possibility of this occurrence was suggested by Lewis in his monograph on valence (7) even before the activity in measuring dipole moments during the last few years gave i t an experimental basis. The phenomenon has been called "partial polarity" by Kharasch (8). This term is unsuitable for the same reason that was mentioned earlier in this paper in the instance of "polar." I suggest that we refer to it as "polar covalence," since it is the kind of covalence that occurs in polar molecules. Freqnently there are involved also the so-called "semi-polar; bonds which have been better named "semi-ionic" bonds by Noyes (9),but the latter are not an essential part of the polar covalence scheme. The apparently arbitrary matter of regarding the displacement of bonding negatrons in a covalent link in the same way as we regard their complete transfer in forming an ionic compound is not serious because the former may involve as much or more energy as the latter. Compare the heats of formation per equivalent of the ionic compounds silver bromide (23.84 Cal.) and potassium hydride (14.1 Cal.) with that of the covalent carbon dioxide (23.6 Cal.), a comparison that indicates that the formation of the covalent bond may involve as much or more energy than an ionic bond. For illustration we shall choose the change of hypochlorous acid to chlorate ion: H 0..
xx
+ 2 0.. I.. : + 3 H
:o: H
-
The formnlas show clearly the state of valence of all the reacting substances and why such an equation may be balanced by the older method of calculating positive and negative valences, a simpler method, to be sure, but one that in itself needs an explanation in terms of negatrons. The formulas with ear-marked negatrons (x) show how the chlorine atoms in two hypochlorous acid molecules take four negatrons from the chlorine atom of the third hypochlorous acid molecule leaving in their stead four negatrons that are displaced toward the oxygen nuclei, thus increasing the state of oxidation of the latter chlorine atom from +l to +5. At the same time these two chlorine atoms acquire complete possession of two negatrons each instead of the two that they had in effect lost in their polar covaleuces, thus being reduced from a valence of +1 each to - 1 each. The oxygen atoms remain in the same state throughout the change. The chlorine in the chlorate ion is obviously incompletely oxidized and the formula predicts the possibility of oxidizing it further to perchlorate ion. The fact that two of the oxygen atoms in the chlorate ion are attached by semi-ionic bonds is not essential to this scheme but is of interest in studying the structure of that ion itself. The value of the concept of polar covalence is obvious. The writer has convinced himself by using i t in his own classes that it is not too involved for general chemistry students. Instead it gives more meaning to the great variety of chemical changes. It is frankly a picture method and it must be used with the same discretion' that necessarily applies to all pictures. But it seems to be just as good for its purpose as are the structural formulas of organic chemistry for theirs. One question upon which this method seems to throw some light, namely, the mechanis* of bleaching with chlorine, may be mentioned. It has frequently been said that the necessity of moisture for bleaching to occur indicates that nascent oxygen is the active agent. We cannot say that the latter has nothing to do with the reaction but certainly this equation leads us to suspect that the active agent is chlorine, probably that in hypochlorous acid. IONS
A year and one-half ago Professor Scatchard (10) read a paper before the Washington meeting of the American Chemical Society on "The Coming of Age of the Interionic Attraction Theory." He and other speakers at that symposium on "Electrolytes" pointed out that as time has elapsed the theory has come nearer and nearer to accounting satisfactorily for the behavior of strong electrolytes and that future work will probably verify the main lines that have already been laid out. Consequently, as the writer pointed out to this
division three years ago (ll), we should discard the old method of writing molecular formulas in our equations for the reactions of strong electrolytes in solution. Also in error is the custom of writing an equation to show the ionization of such a substance when it is dissolved, for the substance does not ionize a t the time of dissolving. Its crystals are composed of ions which presumably dissolve individually. If it should be demoustrated that molecules are present in solution to the extent of a very small percentage of the total substance, a thing that has never been done, then we should regard them as secondary products formed by the union of ions after solution has taken place Since sodium chloride vapor, for example, seems' to be molecular, it appears possible that molecules may be formed in solution also, but the effect of the solvent would limit their formation very greatly. Furthermore these molecules, if present, are unimportant from a chemical standpoint. They would be like the bayous along a river-separated from the main stream in which events occur. In the same category with these misconceptions belongs the old "double decomposition" or "metathesis" reaction. It has no place in the present scheme for reasons that are obvious, not even in cases of weak electrolytes. (12). To soften our criticism of the error of the past we may recall that Arrhenius lived in a molecular era. His theory of ionization followed less than thirty years after Cannizzaro had pointed out the iniportance of molecular weights in determining atomic weights, and only nine years after Victor Meyer devised his vapor density method. There is another misconception regarding ions that may he mentioned particularly. A number of years ago I was shocked to find that metallic silver dissolves readily in warm concentrated hydtiodic acid:and:gives hydrogen gas as one product. It seems to,be a fact that has been known for a long time but ,has been ostracized because it did not fit with the usual teaching of the potential series of metals. In fact, both silver and copper dissolve in apy of the hydrohalogen acids with the evolution of hydrogen. The reason is that the metallic ions unite so completely with halide ions to form complex ions such as AgL- and Cu12that the concentration of metallic cations is diminished sufficientlyso that the equilibrium in the equation:
contains the brown anion, CuBr,?-, as well as other complexes. There is evidence that lead acetate contains complex ions. This explanation disposes of the incongruity of the common interpretation of the color change upon diluting concentrated solutions of ferric thiocyanate or cnpric bromide as an evidence of their being molecular in concentrated solution and ionic in dilute solution. I t disposes also of the existence of "weak salts." a difficulty that may have dampened the enthusiasm of some for the theory of complete ionization. ACIDS, BASES, AND SALTS
We understand an acid to he a substance that dissociates protons, a base one that associates them. An acid may be either a cation, as H1O+, a neutral molecule, as HC1, or an anion, as HSOI-. Similarly, there are cation, neutral, and anion bases, such as aluminum ions, Al(OH)z(H20)r+, and Al(OH)(HzO)s2f NHa and OH-. Water and many other substances are amphiprotic, that is, they may react either by dissociating or by associating protons. All electrolytes are salts, including, for example, a solution of hydrochloric acid, which contains oxonium chloride, H30+Cl-, and sodium hydroxide. A few compounds that dissociate other units than protons have been shown to act as acids (14) but such a phenomenon is too rare and unimportant as yet to justify modifying the theory to include them. This remarkable theory is such a startling and farreaching advance that the definitions of acids and bases that have been current for over forty years seem primitive by comparison. Yet-the writer has found it to be eminently suitable for'use in the general course. The fundamental definitions, however, imply a few changes in several terms that are in common use. The words "strong" and "weak" have been used to mean that an acid or base was much or little ionized. Henceforth they should mean that t h i proton dissociating ability or associating ability is large or small. The terms "acid salt" and "basic salt" become superfluous. They were misnomers anyway. For instance, sodium bicarbonate and disodium phosphate were called "acid salts" but their solutions are alkaline. It would probably simplify o u r nomenclature also if we discarded the term "normal salt." It is unnecessary, al2Ag + 2H80Ca 2Agg++ H? + 2 & 0 though it does not do violence to modem theory. is displaced toward the right rather than toward the One of two principal points with respect to the modem left, as is the case in the normal solutions of the cations theory of acids, bases, and salts to which I should like upon which the potential series is based. to direct attention is its implication for the mechanism In fact, it is a reasonable interpretation that many, of hydrolysis. This has been explained commonly as if not all, the instances of the so-called "weak salts," being due to the ionization of water into hydrogen and such as the halides of cadmium and mercury, may be hydroxyl ions and the reaction of one of these with one accounted for as cases of complex ion formation. The of the ions of a salt to form a slightly ionized comthiocyanate test for ferric iron has been shown to be pound. The modern theory allows us to regard it as due to the formation of the red ferrithiocyanate ion, a reaction with water molecules due to the fact that Fe(SCX)03- (13). I t is probable that the red-brown water is an amphiprotic substance. This is a more color of a ferric chloride solution is due to the oresence reasonable view. I t has alwavs seemed a bit anomalous of a similar ion, FeCla3-. Cupric bromide probably to stress the very small ionization of water in teaching
neutralization and then to base such an important and ubiquitous reaction as hydrolysis upon that same slight concentration of ions. Formerly we said that a salt was acid or alkdme in solution because of hydrolysis. We see now that when a salt solution is acid i t is because one of its ions is an acid, and if it is alkaline one of its ions is a base. The hydrolysis is an incidental consequence of these properties. For example, ammonium chloride is slightly acid because ammonium ion is stronger as an acid than chloride ion is as a base. There is, therefore, competition between ammonia molecules and water molecules for possession of the protons, with the result that some oxonium ions are present: NHa+
+ Hz0 * NHs + HIO'.
Sodium cyanide solution is alkaline because cyanide ion is a strong base whereas sodium ion is almost devoid of acid properties. As the result cyanide ion reacts with water molecules and produces some hydroxyl ion : CN-
+ HIO Ft HCN + OH-.
We find in the literature that ammonium cyanide is said to be about 40% hydrolyzed~bviouslyan inaccurate statement because the extent of hydrolysis is different for each ion and should be stated for each separately. Ammonium cyanide solutions are in reality alkaline, which indicates that the second of these reactions goes to the right farther than the lirst, cyanide ion being a stronger base than ammonium ion is an acid. The small increase in hydrolysis that is caused by rise in temperature has been interpreted as due to the increased ionization of water. Instead, we may now say that the greater hydrolysis is due to the increase in the effective concentration of water molecuIes caused by the progressive decrease in their association with each other. There may he several different kinds of reactions that have been called hydrolysis. Pehhaps the hydrolysis of an organic compound, such as an ester, involves an entirely diierent mechanism, but that does not fall within the scope of our concern a t present. The second point of importance under this topic is that the modern theory of acids makes it necessary that we consider seriously the hydration of ions. Our chemistry of the past has occurred mostly in water solution, and yet in writing equations for the reactions we have usually neglected the function of the water. The soluble inorganic hydroxides are probably mostly salts, which means that they are composed of metal cations and hydroxyl anions. However, the insoluble hydroxides are probably molecular, being composed of coordiiation complexes containing both hydroxyl radicals and water molecules. The complex acts as an acid by dissociating protons from its water molecules and as a base by associating protons with its hydroxyl radicals. These changes in the case of aluminum hydroxide are shown by the following equations:
+ OH-+ A1(OH)4(H20)r-+ H?O, aluminate ion AI(OH)dH2O)r + 2HxO+ Al(&O)P + 3H90. AI(OH)a(H10).
+
aluminum ion
The hydrolysis of aluminate ion and aluminum ion is represented by the reverse of these two reactions, the water acting molecularly as an amphiprotic substance. Data regarding the hydration of ions are inadequate, hut sufficient so that this interpretation may be used satisfactorily. In this connection Pauling (15) has shown recently that stannic acid is Sn(OH)p(HzO)z, the stannates containing the ion Sn(OH)P, and that antimonic acid is Sb(OH),(HzO), the anion being Sh(OH)eM. This is the anion that has previously and incorrectly been called "pyroantimonate." The greater emphasis that we must now lay upon water of hydration adds further reason for the desirability mentioned earlier for using negatronic formulas to explain chemical properties. In these coordination compounds the metal ion shares usually either an octet or a dodecet of negatrons from the oxygen of the water molecules. ATOMIC WEIGHTS FROM ISOTOPIC MEASUREMENTS
In an earlier paper the writer reviewed the Aston method of determining atomic weights (16). This method is based upon the discovery by Aston in 1930 of a reasonably accurate method of determining the percentage composition of isotopic mixtures of the complex elements. From this information and the isotopic masses, which may be determined by the mass-spectrograph, it is possible to obtain,thezttomic weight of the "chemical elemht" by simple calculation. Although the operation of the mass-spectrograph requires a refinement of technic that is beyond the comprehension of general chemistry students, its principle is simple and is readily understood by them. The method is, therefore, peculiarly advantageous for presentation in the early part of the course. Such presentation places atomic weights upon a concrete experimental basis and removes from the students' minds most of the mystery that was formerly associated with them because of the complexity of the Cannizzaro method. Since the paper referred to above (16) was written the third and fourth reports of the Committee on Atoniic Weights of the International Union of Chemistry have appeared (17). Only two changes in atomic weights were made in 1933, both of them being the result of chemical determinations. The report, however, includes a brief review of the Aston method and comments on the striking concordance of the two methods. The 1934report makes changes for eight elements. In the cases of four of them (As, Se, Te, Cs) the values adopted correspond exactly or closely to the results of the mass-spectrographic method. The changes were made primarily because the older values did not agree with those of the latter andrecent more careful chemical determinations were found to do so. It may be
noted that inaccuracies in the old method are caused frequently by impurities in the material, a source of error which is of much less importance in the Aston method. The 1934 report states also that the atomic weights of carbon, columbium, and tantalum which are now in use differ from those obtained by the Aston method. Their early revision may be expected. Also it states that the ~reviouslyadopted' value for thallium is rebecause ofaagreement with Aston's value tained in spite of chemical determinations that alone would indicate a lower figure. These data indicate the importance that the method
has attained in a very short time. Its usefulness in general chemistry teaching seems to be obvious. CONCLUSION
The reading of this paper has been an attempt to set forth the need of a fundamental revision of the general course not only by affirmation, but also by pointing out in some detail the contrast between the theoretical structure that has been used and that which may well be used. It has been impossible to mention all parts of our voluminous subject, but those that were chosen have, perhaps, the most strikmg implications.
LITERATURE CITED
RoDEBusn, W. H., "The electron theory of valence," Chem. Rev., 5, 511 (Dec., 1928). ARMSTRONG, H. E., Chapter in THORPE,J. F.,"Chemistry in the twentieth century," The Macmillan Co., New York City, 1924, H. E., ;bid., p. 122 p. 88. ARMSTRONG, GAMOW,G., "Modern ideas on nuclear constitution," Noture, 133, 744-7 (May 19: 1934). LANDE, A,, "The neutron," Scz. Suppl., 8 0 , s Ouly 6 , 1934). H., "The complex neutron," Phys. Rev., 46, MARGENAU, 107-10 (July 15, 1934). ANDERSON, C. D., "The positive electron," ibid., 43,4914 (Mar. 15, 1933); 45, 3M (Mar. 15. 1934). WnDMAN, E.A.,"Nomenclature of the electron," Sci., 78, 191 (Sept. 1. 1933). N. V., "The covalent link in chemistry," Cornell SIDGWICK, University Press, Ithaca, New York, 1933, pp.. 51-61. LEWIS,G. N., "Valence and the structure of atoms and molecules, Chemical Catalog Co., New York City. 1923, pp. 83 and 150. Knmnscn, M. S. AND SEER.B., "Electronic conception of valence and heats of combustion of organic compounds," J. Phys. Chem., 29, 625-58 (June, 1925). KHARAsCn, M. S. AND DARKIS,F. R., "The theory of partial polarity
of the ethylene bond and the existence of electra-isomerism," Chem. Rev., 5, 571-602 (Dec., 1928). W.A.. "The electronic structure of lnoreanic com1Ql NOYES. nlex&." J. ~ m Chem. . Soc.. 55.4889-93 (~ec.,~1933) G., "The coming of age of the interionic at(10) SCATCHARD, traction theory," Chem. Reu., 13, 7-27 (Aug., 1933). 11 11 WV.nwAN. 13. A.."Modern concentions and the teachine of \-,
~
~
see WILDMAN, E. A:, he double deco&positi&
reaction;" Proc. Ind. Acod. Sci., 41, 1931 (Dec., 1932). 112) H.-I. ~AND- VAN H. B.. "The \--,Scur.asrwr.~n. ~, ~ - VALKENBURGH. structure of ferric thiocyanate and the thbcya.n& test for iron." J. A m . Chem. Sac., 53, 12124 (Apr., 1931). E. A., 10c. ~ i l .reference , ( I l ) , pp. 96-7. (14) See WILDMAN, (15) PAULING,L., "The formulas of antimonic acid and the antimonates," J. A m . Chem. Soc., 55, 1895-1900 (May, (12)
~
,""?\
'"lY",.
(16) WILDMAN, E. A , "Teaching atomic weights," J. CHEM. EDUC.,10, 23840 (Apr., 1933). (17) BAXTER, G. P., CURIE,M., HONIGSCHMID, 0..LE BEAU,P., AND MEYER,R. J., Third report, 3. A m . Chem. Soc.. 55, 441-52 (Feb., 1933). Fourth report, ibid., 56, 753-64
