An EVALUATION ofthe STRUCTURAL THEORY of ORGANIC CHEMISTRY.' I JAMES K. SENIOR Gwrge Herbert Jones Laboratory, The University of Chicago
T
HE PURPOSE of the present course, as explained to me, is t o exhibit to organic chemists some of the recent progress in other branches of chemistry, and to suggest how this new knowledge may aid in the solution of problems within the organic field. The organizers of the course have thought fit to open the series with an introductory talk intended to show how far organic chemists have already advanced as a result either of their own efforts, or of assistance given them in the past. This lecture will therefore treat the following questions : (I) What are the ultimate aims of organic chemistry? (2) To what extent have these aims already been accomplished? (3) What remains to be done; in particular what are the unsolved organic problems upon which# is hoped that other scientists may throw light? The aims of organic chemistry are, so far as I can see, no different from those of chemistry in general, and the objective may well be envisaged by considering an imaginary future in which experimental chemistry is to be a finished science, and all possible facts called chemical are to be deducible from data already known. Of course I have no notion that any such state will be reached within a finite time, and no reasonable person would expect that more than slight progress toward this goal should already have been made. But present accomplishments may be compared with the proposed ideal and from the comparison may be obtained hints as t o the direction of current chemical effort.
* Introductory lecture of a series dealing with organic chemistry in the light of the present-day physical andchemical theories, delivered at The University of Chicago duripg the summer quarter of 1334. (June 19th.) Although the lecture as delivered is a coherent whole, it seemed necessary, because of its length, to divide it into two parts for publication. ~h~ part will appear in the following number.
If chemistry had reached the finished state indicated, the following conditions would prevail. There would be for every chemical compound a formula which would: (1) uniquely identify the compound in question; (2) permit the determination (either by inspection or calculation) of all the physical properties of the compound formulated, as well as its reactions with all other compounds for which similar formulas were given. To stress the formulas of chemistcy as opposed t o chemistry itself may perhaps cause some surprise. But I make no apology for so doing. One hundred fifty years ago Lavoisier asserted that a science and the language of that science are two "imprints from the same type"; and today it is almost impossible t o imagine any precise idea for which a linguistic expression but no suitable symbolic representation can be found. As far as theoretical chemistry is concerned, its formulas constitute its language, and its language constitutes the science. This lecture will therefore deal with organic chemical formulas. What do they tell; what might they tell; how may they be improved so that they will tell more than they now'do? But i f a o limitation other than the one just stated were placed on the discourse, it would have to include a great deal of speculation which anyone may perform for himself. The topics mentioned will therefore be considered only within the framework of the atomicmolecular hypothesis as now generally accepted. About what will happen to chemistry and chemical formulas if this hwothesis is ever abandoned.. vou already know as much as I do. ~h~ two main purposes of a chemical formula are: (1) the identification of the compound formulated; (2) the precise determination either implicitly or explicitl~of all the physical and chemical (that is, reactlve) properties of the compound in question. So
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far, these two desiderata have been mentioned in equal terms, but a little consideration suffices to show that the first is far more important than the second. A formula which gives only fragmentary information about the compound to which it refers may still be very sewiceable. If it leaves in the mind of the chemist any doubt about the identity of the compound symbolized, it is well-nigh useless. A convenient method of treating the subject is, however, to put the cart before the horse and to begin by a discussion of organic formulas with respect to their usefulness in recording and predicting properties and reactions. It will be assumed for the moment that they do uniquely identify the compounds to which they refer, and the question how far this assumption is justified will be taken up later on. The simplest formulas which need be considered here are those usually called molecular, such as C4Hlo or GHBO. Formulas of this k i d were devised as soon as the atomic-molecular hypothesis was proposed, and were intended to record only analytical data-the results of certain particular forms of reactivity. It is of course essential that all analytical processes admitted to be appropriate for a given compound should lead to the same molecular formula; otherwise no formulation in accordance with the atomic-molecular hypothesis would be possible. Chemists have, however, dodged this diiculty by what a t first sight appears to be a trick. When various analytical methods give discrepant results for the same compound, it is never concluded that the compound in question has no unique molecular formula. Instead, all but one of the conJlicting methods are declared to be inapplicable. But, so far as I know, in every well-investigated instance, good grounds have been found for the exclusion of all but one set of compatible procedures. Hence the practice, which has the superficial appearance of chicane, is not in fact a subterfuge employed to save the face of Dalton's theory. It was early recognized, however, that analytical data by themselves are usually'insufficient to justify a molecular formula; because of &e phenomenon known as polymerism, determination of the molecular weight is also necessary. Here the physical chemists have rendered invaluable service to organic chemistry. In so far as compounds can be vaporized or brought into dilute solution without decomposition or dissociation, the question of molecular weight may be regarded as practically settled. But pure liquids and solids are still problems, partly because of unwise extension of the field in which the term molecule is applied. Present conditions would, I thimk, justify two statements: (1) It is doubtful in many solids and perhaps some liquids whether a unit can be found which corresponds in any useful way to a single molecule in the gaseous or dissolved state. (2) Where such a unit can be identified, its molecular weight is frequently not the same as the molecular weight of the same substance in the gaseous condition or in dilute solution. The absence of precise information in regard to the
molecular weights (if they exist) of solids has been of little hindrance to organic chemistry. The organic chemist needs formulas for compounds in their reactive states, and all except a minute fraction of known reactions occur in the fluid phases. But association in liquids, the solvation of solutes, and indeed the whole chemistry of concentrated solutions present difficulties which have never been entirely overcome. These are of course classic problems in physical chemistry, and a great deal of earnest thought has been devoted to their elucidation; but the organic chemist still needs, and would welcome, much more information on these points than he has yet received. During the remainder of this lecture attention will be confined largely to the question of the adequacy of formulas for dispersed substances. The main problems to be here discussed really begin with the recognition that, for most carbon compounds, a molecular formula, as fixed by percentage composition and molecular weight, is an inadequate means of registering anything besides stoichiometric data. Such a formula in general does not uniquely determine the compound to which it refers, and gives almost nothing about reactive properties. As far as the second defect is concerned, organic chemists might have limped along with these unsatisfactory molecular formulas, but recognition of the widespread occurrence of isomerism forced them to elaborate their symbolism. Within a few years after the first isomers were discovered, Berzelius made a suggestion which still guides organic chemistry. He proposed that, since the molecules of isomeric substances contain equal numbers of atoms of like kinds, the differences in the properties of such substances be accounted for by differences in their intramolecular arrangements or structures. So far as I know, no one has ever seriously considered whether there exist hypotheses other than that of Berzelius which might also explain isomerism. The extraordinary success of the structural theory has diverted the efforts of organic chemists into a single channel. I have no alternative to suggest, but it is nevertheless well to remember that Berzelius was only a chemist of extraordinary ability, and not a prophet with a revelation from on high. Between the acceptance of the general idea that isomerism is caused by differences in intramolecular arrangement and the discovery of a particular scheme of arrangement adequate to account for observed isomers there is a wide interval. The history of organic chemistry between 1835 and 1865 might be epitomized as a search for such a scheme. The first great step toward a solution of the problem was the theory usually associated with the name of Kekule, although several other investigators contributed to its constmction. This idea is one of the most remarkable generalizations which has ever emanated from the human mind. No true appreciation of the subsequent successes and failures of organic chemistry is possible without an understanding of the essential content and limitations of the Kekule stmctural theory.
The formulas based upon this theory tell whether any two given atoms do or do not lie "next" to one another in the molecule. There can be little doubt that Berzelius conceived of the intramolecular arrangement as an arrangement in three-dimensional Euclidean space. Probably Kekul6 held similar views, but his theory is independent of any such limitation. Logically considered, adjacency or nextness is a symmetric, irreflexive,non-transitiverelationwhich does not necessarily require a space interpretation. On the map, Indiana is next to Illinois and not next to Iowa; on the calendar Tuesday is next to Wednesday and not next to Thursday; in the army, first lieutenancy is next to captaincy and not next to majority. Iu the number 24, six is the next factor larger than four. One great beauty of the structural theory is that, though it assumes a relation of adjacency between atoms, it need postulate nothing concerning a manifold in which the discrete atoms may be embedded. The practice of organic chemists has been to picture such adjacency relations as space relations, and to assume that the particular space involved is the one treated in the high-school textbooks. This notation is doubtless the most convenient yet discovered; indeed it may be questioned whether a handier one ever will be found. But mere convenience should not lead to a confusion of the essential idea represented with the fortuitous peculiarities of the conventional representation. As far as the structural theory is concerned, there is no need to assume that intramolecular space is Euclidean, nor even to assume that atoms and molecules are localized in either time or space. It may be that they are so localized, but if it were to be proven tomorrow that they are not, the structural theory would continue to hold with undiminished force and accuracy. However, if the structural theory is independent of space considerations, what does it tell about any particular substance to which it is applied? All it gives is a set of adjacency relations between the discrete atoms (finite in number) which compose each molecule of that substance; hence the question amounts to asking "Have such sets of relations ever beynamed?" The answer is "Yes." Mathematicians have devoted to these systems an exhaustive study and their findings constitute an important part of what is known as Analysis Situs or Topology. Every such set of relations may be embodied in a diagram and moreover (by the use of convenient devices) in a two-dimensional diagram. Structural formulas are analysis situs or topological diagrams of molecules. From this fact follow a t once certain conventions which are annually explained in every first-year course on organic chemistry. In topological diagrams the lengths of the lines and the magnitudes of the angles are without significance. Hence, in the structural formula for ethane, it makes no diierence whether or not the six carbon-to-hydrogen lines are drawn all of the same length. The adjacency relations are independent of such variations in notation. Again, in the diagram for propane, . the mamitude of the angle between the carbon-to-carbon bonds is immaterial. The substance is
the same propane in any case. Everyone admits the insignificance of such details, and this admission amounts to recognizing that the system used is not restricted by all the postulates of ordinary Euclidean geometry. The question then at issue is: "How far are the topological diagrams called structural formulas successful in describing the substances to which they respectively correspond?" Here a distinction must be made between the properties used to determine the formula under consideration and those not so used. The structural theory, in so far as it accounts only for properties of the first kind, cannot claim to be more than an ingenious method for registering empirically determined facts. When it transcends this limitation, it ceases to be a mere notation and becomes a theory serving the main purpose of all scientific theories, prediction. But though notation is here subordinated to theory, the invention of a notation so successful as that employed in the structural theory is by no means a trivial feat. It is highly astonishing and highly creditable to the acumen of Keknl6 and his contemporaries that so simple a notation as a topological diagram should so frequently serve as a workable scheme for recording a, considerable portion of the reactions of the substance to which the diagram refers. In other words, it is surprising that, from the reactions of a compound, there can usually be obtained a uniquely determined topological diagram which, though it may shed little light on much of the behavior, is nevertheless not in contradiction with any known reaction of the substance in question. Nor should discredit be attached to the inventors of the scheme because their original idea does not always work perfectly. 'Several classes of compounds are known, among them the phenyl (and other similar aromatic) derivatives, as well as the so-called tautomeric mixtures, for which every static structural formula yet found conflicts with some part of the behavior of the substance formul%ted. And here the introduction of subsidiary dynamic hypotheses has proven sufficientto account for the facts. This subject will be more fully discussed later on. A large part of the literature of organic chemistry might he described as commentaries, in particular iustances, on the relative success or failure of the structural theory (with its implied-formulas) as a means of registering or predicting chemical properties. Obviously a general discussion of this question is impossible in a single lecture. Both the strong and the weak points of the theory can, however, be illustrated by a brief treatment of one topological item, the double bond. Here two questions arise: (1) Why is a double bond put into a structural formula? (2) What reasoning leads to the location of this symbol a t a particular point in the diagram? Unhappily, organic chemistry is not in such condition reply can be ~ i v e n that a brief and uniformly . applicable -. to either query.
Let us begin with ethylene. In its structural formula, both the presence and location of the double bond are dictated by the postulates that carbon is quadrivaleutand hydrogen univalent. Further investigation shows that ethylene differs from many other compouuds in that, under proper conditions, it adds hydrogen so that its molecular weight is increased by two. With compounds of the formula C3Hhcomplications arise. The structural postulates limit the numher of compounds to two, one with a double bond, the other with a three-membered ring; and in fact two hydrocarbons, C3H6,are known. Judging by experieuce with ethylene, the one with the double bond should add hydrogen; but this reaction fails as a proof of formula, for both substances add hydrogen to give propane, though with different degrees of readiness. To determine the structure of propylene, recourse must be taken to more complex data-notably the number of isomeric substitution derivatives. Thus the double bond registers more experimental facts in the formula of propylene than i t does in that of ethylene. With compounds of the formula C4H8,the complications become still greater, and not only the presence but also the location of the double bond is of significance as a record of observed reactions. Such are the relatively simple cases. The real difficulties begin when the molecular weight gets so high that the best analytical results are no longer of clear significance. A compound with the formula. C4oHe contains 0.3% more hydrogen than one with the formula C4~Hao.This difference lies just outside the probable analytical error, assuming that the sample analyzed is perfectly p u r e a n assumption which, however, is rarely admissible in compouuds of high molecular weight. Under these conditions very little can be deduced from the stoichiometric findings alone. How then is it to be decided whether a double bond is present or not? Various methods might be suggested. The one here chosen would probably be considered by most chemists to be as good as any, and by many to be preferred. E Experiments with substances of lov molecular weight show that when the structural formula contains one double bond, the compound usually adds one mole of hydrogen. Unfortunately, structures involving a single cycle sometimes do the same thing, so that the test is not a positive one. Moreover, among unsaturated compounds wide divergences between the rates of ad& tion appear. Minute traces of impurity frequently exercise pernicious effectson catalysts. If a compound fails to add hydrogen, does that fact indicate beyond doubt that no double bond is present? It must be candidly admitted that complete certainty on such points is denied to the organic chemist in the present state of his science. He may however arrive a t a conclusion which is highly probable. His hydrogen addition test is a good, though not a certain, indication of the presence of a double bond. To confirm his decision, he may appeal to the empirically determined rules regarding indices of refraction, melting points of
compounds with closely related formulas, addition of halogens, oxidation reactions, etc. He is nearly sure to arrive eventually a t a conclusiou which satisfies all critics. But when he has so arrived, no one can tell without reading the details of his procedure just what behavior the double bond in his formula is supposed to record; thus until the method is specified, the predictive value of the symbol is indeterminate. Suppose, however, that this difficulty is dodged by an assumption which I consider quite arbitrary and which I introduce merely to simplify the argument. Forgetting ring compouuds, poisoned catalysts, and all other complications, let it be assumed that the formulas which contain double bonds correspond perfectly with the compounds which add hydrogen-in other words that the presence of the double bond in any formula records the positive outcome of the hydrogen addition test. Under these highly idealized conditions, what would be the predictive value of this symbol? Usually a compound which adds hydrogen a t a double bond between two carbon atoms also adds halogens a t the same point. The correlation is good but by no means perfect. Neither is the correlation equally good for the addition of all the different halogens. For the addition of halogen acids it is worse, though still pretty fair. Furthermore, if there is but one double bond in the compound, that is frequently the preferred point for the attack of oxidizing reagents. But there are plenty of exceptions. The worst weaknesses of the theory appear, however, when more detailed questions are asked. Suppose a double bond, the presence of which is determined by the hydrogen addition test, does absorb bromine. How firmly are the two bromine atbms held? In such cases one may well throw up one's hands. The literature is studded with little rules-small generalizations which hold good over small ranges, the limits of which are imperfectly known. Before long, the answer to a question becomes a matter of opinion as to the relative force of conflicting analogies, and the -judgment of the best organic chemist is good only within the range of his personal experience. So much for the double bond. The picture is none too bright, and yet this symbol is among the most successful of those used in structural formulas. Lack of time forbids detailed discussion of others, but there is scarcely one, the value of which exceeds that of the double bond, while many are much less successful as devices for either recording or predicting. It is hard to criticize this state of affairs without appearing unjust or ungrateful to preceding generations. I would be neither. Whatever order exists in organic chemistry is due to their efforts, and, far as the present system may lag behind what is needed, without i t there would be chaos. A good organic chemist applies his fragmentary knowledge with judgment and discretion; a poor one does not. In my opinion a fair summary of the situation is about as follows. As records of the observed reactions which determine them, structural formulas are of limited
usefulness. Their chief defect is that they indicate not particular reactions but rather classes of reactions, any member of which might possibly have been used. Unless the method of determination i t specified, any attempt to predict from such a formula is apt to result in a vicious circle of reasoning. Even with this difficulty obviated, the predictive value of structural formulas, though by no means nil, is a mere fraction of what is desired, and is never sufficient to establish more than a high probability. Let us turn next to certain quasi-historical considerations. Approximately fifty years have elapsed since the structural theory received its severe test a t the hands of von Baeyer. During this half-century chemists have not learned to write a better formula for indigo than von Baeyer wrote, nor to read from van Baeyer's formula much more than von Baeyer was able to read. Throughout this period the progress of organic chemistry has been almost entirely extensive. It is possible today to write many more structural formulas than von Baeyer could write, and with a high degree of assurance to assign structural formulas to compounds far more complex than any which von Baeyer could have handled. But when all is said and done, the modern procedure is not different from his. It is merely carried out oftener, faster, and in more difficult cases. Various reasons, depending largely on the temperament of the reasoner, might be given for the failure of organic chemistry to make any considerable intensive progress. My own view is that the chief cause is to he found in the continued adherence to a form of notation due principally to C N Brown ~ and still in very wide use. Crum Brown adopted the dot as a symbol for the atom and the straight line as a symbol for valence. Since atoms of different elements sometimes have the same valence, he was forced to discriminate between the various sorts of (say) bivalent atoms by labeling his dots in various ways, and the Berzelius letters for the elements were a natural choice for Such discriminatory symbols. He might, however, just aspwell have adopted a polychrome notation or any other similar device; the form of the letter symbol has nothing to do with the nature of the atom symbolized. In my opinion, the failure to read out of dot-atom line-valence formulas much more than von Baeyer could read makes i t highly probable that von Baeyer had already practically exhausted the possibilities of such formulas. Certainly I cannot prove this contention, hut I think organic chemistry is not likely to make much intensive advance so long as no more complex system of notation is adopted. To speculate in armchair fashion on the form which changes might advantageously take is easy enough. Structural formulas have a number of degrees of freedom. Considering only the valence lines, the lengths of these lines and the magnitudes of the angles between them are without significance in topological diagrams. If a meaning were attached to these features, much more information could be recorded by the formulas,
and much more deduced from them than is now possible. For example, if organic chemists had (as they do not yet have) a means for breaking any valence bond a t will, and measuring the energy necessary to disrupt the molecule a t the point in question, the amount of this energy (or better, its reciprocal) might well be expressed by the length of the valence line. Similarly, the magnitudes of the angles between the valences might also be valorized in a variety of ways. But though it is easy to make such theoretical suggestions, to find one which under existing conditions can be uniformly applied is a most difficult task. For twenty-five years (at least) organic chemists have been experimenting along this line. Usually they have not tampered much with the dot-atom, but have devoted their attention to devising a symbol for valence which should he more informative than the straight line of the classic theory. A number of so-called electronic theories have been proposed, and the variety of notations suggested for expressing a few not tw complicated ideas is fairly bewildering. But these apparently distinct views, when stripped of the picturesque language which disguises them, turn out to have a strong family resemblance. The length of the valence line is to indicate in some manner (about which there is still no unanimity of opinion) the energy involved in the union of the two atoms which it connects. On the straight line valence is to be placed a cross-hair, the position of which is intended either to indicate the behavior of the molecule when it is split by a polar reagent a t the point in question, or (if the valence is one of a double bond) to show the direction of addition of a polar reagent. An example will perhaps make the idea clearer. Fluorenone may he hydrolyzed to diphayl-2-carboxylic acid.
If this behavior were indicated by the symbol (A), then the symbol (B) would call for the reaction
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033 OF//-up C
II
0
GZ
H-C 0
II 1
0H
(B)
11
0
which, as a matter of fact, does not occur. If both acid and aldehyde were produced simultaneously, the crosshair would be placed somewhere along the lme in a position to show the relative proportions of the two reaction products. The difficulties inherent in such a svstem are considerable. First, in directed addition or hydrolysis, the proportions of the reaction products often vary with changes of temperature, pressure, etc. That is, a straight line with a fixed cross-hair is not a symbol for
a particular V B ~ C ~bond C ~ a t all t i e s , but for that bond under definite physical conditions. Furthermore, even a t a given temperature, the proportions of reaction products sometimes vary with the reagent used. Hence the position of the aoss-hair is affected not only by the physical but also by the chemical environment of the molecule. In view of such complexities, progress toward the development of a self-consistent system has naturally been slow. But beyond these inherent difficulties, many organic chemists have been further hampered by a strange predilection. For some reason they have chosen to identidy their cross-hair with the electron or the pair of electrons of the physicist. The misery which this infatuation has caused them is hard to estimate. They have become involved in problems of electrodynamics, spectroscopy, wave mechanics, etc. Since many of them have never had any training in such subjects, the outcome illustrates the unfortunate results which follow the attempt to "madly squeeze a right-hand foot into a left-hand shoe." No generally accepted system has yet resulted from these theories of valence which are usually called electronic, but which I prefer to call cross-hair theories. However, the reasons for attempting to advance in this direction are (as I hope to have shown) well founded and the results fairly deserve to be called promising. If organic chemists can ever be induced to develop the notations suitable to their own needs without regard to the quite distinct needs of other disciplines, much may be expected. Moreover, once they have taken this step, they may look hopefully for aid from their fellow scientists. As long as they remained wedded to their classic symbols, it was improbable that any outsider less experienced than themselves in manipulating these ideographs could be of much help to them. Having abandoned this practice, and having adopted a form of statement calculated to reveal, rather than to blur, the outlines of their problems, they may well find that considerable light on these 'matters is to be obtained from persons who are not prosptrtive contributors to future editions of Beilstein. A little friendly cooperation between scientific equals is likely to be more effective than much intellectual servility.
METHODS of WEIGHING by SWINGS. H. L. LOCHTE University of Texas, Austin, Texas
RECOGNIZED methods of accurate weighing with the analytical balance may be grouped into five-swing, equal-swing, and single-swing methods. The last two of these are often used but are not entirely satisfactory in the hands of the undergraduate student using the typical high-grade balance. The five-swing method is usually recommended in textbooks, but experience with data obtained with a number of sets of 5 swings indicates that the rest point calculated from a single set of 5 swings may differ from the average of 3 such sets by as much as 0.1 mg. Since the use of 3 sets of 5 swings makes weighing excessively tedious and time-consuming, especially when several students have to use the same balance, a study of various swing methods was undertaken in an effort to avoid the use of such an expensive method. Eight balances were selected a t random from a group of 42 balances bought since 1926 and in use by sophomore and junior students in courses in analysis. Three sets of 5 swings were obtained for each balance first with no load and then with 1 mg. overload. The 48 sets of data were then used in a study of the relative accuracy of 5-swing, 3-swing, and Pregl deflection data. In this. way 96 sets of 3-swing and Pregl data were obtained from the 48 sets of 5-swing data. The study shows that: (1) a single set of 5 swings often introduces an error of about 0.1 mg. due to poor reproducibility of rest point; (2) the average of 3 ,sets of 3 swings gives almost as reliable results as the average of 3 sets of 5 swings; (3) the average of 2 or 3 sets of Pregl deflection data agrees well within 0.1 mg. with the average of 3 sets of 5 swings and is much more rapidly and simply obtained. Experience in the use of the, Pmgl scheme with classes of 30 and of 230 students has been completely satisfactory, provided the balance is given a few minutes to, permit temperature equalization, the first swing is not used, and the balance is completely arrested betweem sets of swings.
DIVISION OF CHEMICAL EDUCATION-SAN
FRANCISCO
. 11 :2& 8. The Award of the High-school Chemistry Prize by. Wednesday Morning and Aflnnwn: the Chemistry Section of the A. A. A. S. (Pacific Division).. 9:O& 1. H. W. STONE. What Percentage of College Stndents Think? Do Your Students Think? 12:3&Divisional Luncheon. 2:0& 9. 0. M. SMITH, L. F. S H E EA ~N L A. ~ BURROWS~. 9:2& 2. E. F. DEGERING.Review Outlines as an Aid in the Teaching of Chemistry. Some Measurements of Laboratory Achievement in First3. P. A. LEIGHTON AND F. G . ANIBAI.. A Plan to Year College Chemistry. 9:+ Eliminate the Overlapping in High-school and College 2:20--10. T. G . THOMPSONThe Catalyst, a SeaGoig Chemistry Courses. Laboratory. AND D. J. H E N ~ S S Y A . Method 2:40--11. L. J. Woon n m C. W. FLm~wooa.. The Use of 10:00-- 4. J. B. MUENZBN for the Administration of Individual Assignments in ChemiSodium Paraperiodate far the Detection of Manganese h the Beginning Qualitative Course. cal Problems. 10:2& 5. ROBERT DuBors. The Ferric Thiocyanate Equi3:*12. N. D. C~i~nohns.Science InstFuction in the New libria. Chicago City Junior Colhpps 10:6. FLORENCE E. WALL. Training in Chemistry for 3:40--13. E. F. DEGEEING.The Intuitive Sense. the Cosmetic Industrv. 4:0@-14. L. A. TEST. A Periodic Table for LaboratomDisplay Constmctedof tbcElemnt%andTheir Cbmprmnd;. AND J. W. INCB. Twelve Years 1 7 R. K. C-&ON Business Meeting. of a Chemistry Contest.
