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(28) Varteressian, K.A., Thesis, Pennsylvania State College, 1930. (29) Walker, Lewis, and McAdams, “Principles of Chemical Engineering,” 2nd ed., McGraw-Hill, 1927. (30) Walker, Lewis, and McAdams, Ibid., p. 600. (31) Washburn, E. W., Bruun, J. H., and Hicks, M. M., Bur. Standards J . Research, 2, 4iO (1929).
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( 3 2 ) Whitmore, F. C., and Wrenn, S. A I . , J . A m . Chem. SOC.,53 3136 (1931). (33) Young, S., “Distillation Principles and Processes ” p. 5 2 . Macmillan, 1922. RECEIVED October 13, 1931.
Characteristics of Vanillin and Coumarin R. M. HITCHENS, Monsanto Chemical Works, St. Louis, Mo.
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AXILLA-LIKE flavors may be of three kinds: vanilla extract prepared by extracting 13.35 ounces of vanilla beans with 1 gallon of alcohol; imitation vanilla extract containing less than enough vanilla extract to account for 50 per cent of the flavoring strength or even none a t all; and vanilla-vanillin and coumarin which must contain enough vanilla extract to contribute at least 50 per cent of
Ethyl alcohol-water and glycerol-water mixtures were made from good grades of commerical ethyl alcohol and glycerol. They were analyzed by specific-gravity measurements. The solubility determinations were made as follows: The solvent and excess of the solute were placed in small flasks fitted with mechanical stirrers. The flasks were supported in a water bath, 8 the temperature of which was maintained constant to 0.2”C. The contents 20 4 7 of the flasks were stirred vigorously for 6 hours to 24 it 6 insure saturation of the f ?3 s o l u t i o n s . Solutions j 20 .5 m a d e i n this m a n n e r cf u 2 proved to be of the same 16 concentrations as those p r e p a r e d by s t i r r i n g 3 2 s u p e r -s a t u r a t ed so5 12 z3 lutions a t the d e s i r e d 3 temperature. They are, > d 2. therefore, saturated so5 lutions. 0.6 I S a m p l e s of the solutions were o b t a i n e d by means of pipets kept 0 P E ~ C E NLTy n n A i c o n o ~ 0 v VOLVUE warmer than the soluFIGURE 2. DATAON COUMARIN IN ETHYL tion to prevent crystalFIGURE1. DATAON VANILLININ ETHYL ALconoL SOLUTIO~S ALCOHOLSOLUTIOKS lization in the p i p e t s . The tips of the p i p e t s the flavoring strength. The latter is also sometime> labeled were well covered with absorbent cotton to prevent contamination of the samples with undissolved substance. “vanilla compound extract.” Flavors of the above types are largely used in baking and in It was found convenient to analyze the vanillin solutions by the manufacture of confectionery and ice cream. titrating potentiometrically the phenolic hydrogen with For many years the principal solvent used in making up standard sodium hydroxide solution. The 0.1 N silver chlothese mixtures has been alcohol. However, in recent times ride electrode was used as a reference and a stick of antimony there have been many attempts to decrease the amount of alcohol used or to employ a substitute for either all or part of the alcohol, owing to government restrictions on the use of the latter solvent. Glycerol has been one of the principal substitutes used. In attempting to formulate so many different mixtures, there have been numerous cases of precipitation troubles reported, especially in cold weather. Obviously, the solution of such problems depends upon the solubility of the various solid constituents in the particular solvent mixtures used, and it is with a view to completely rounding out previously published data of this kind ( 1 , Z ) that the solubilities presented in the accompanying graphs were determined. The experimental methods employed differ somewhat from the usual and are described in detail below.
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Since commercial vanillin and coumarin are of a high degree of purity, such material was used without further purification.
PERCLNT GLYCEROL BY W a G - 7
N GLYCEROL FIGURE 3. DATAo s V ~ T L L IIY SOLUTIONS
I N D U S T R I A L A N D E N GI N E E R I N G C H E M I S T R Y
April, 1932
served satisfactorily in determining the end point. I n this way rapid analyses could be made with an accuracy of 1 per cent. The ethyl alcohol-coumarin solutions were analyzed by extraction of the coumarin with chloroform and evaporation of the solvent under reduced pressure a t room temperature
QiaCwr
FIGURE 4.
G L ~ C E R0O r LL V E G H T
COUMARIS SOLUTIONS
DAT.4 ON
IX
GLYCEROL
and drying over phosphorus pentoxide. Preliminary experiments showed this method to be valid for the glycerol solutions also, since less than 1mg. of glycerol is extracted from a 10 per cent glycerol-90 per cent water mixture by four 10-cc. extractions. The results have been summarized in four sets of curves in which the ordinates are grams of solute per 100 cc. of solution, and the abscissas are the percentages of glycerol or of ethyl alcohol in the solvent. There is a separate curve for each temperature.
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Figure 1 shows the data obtained with vanillin in ethyl alcohol-water mixtures. It is apparent that the solubility is low in cold dilute ethyl alcohol, but it rises rapidly as the concentration of ethyl alcohol increases and as the temperature rises. Most of the values in 70 per cent ethyl alcohol fall far above the graph, the highest being 76.7 grams per 100 cc. of solution a t 40" C. The data a t 50" C. were not completed, since vanillin melts under ethyl alcohol solutions a t this temperature. Figure 2 presents the results with coumarin in ethyl alcohol solutions. Coumarin is obviously much less soluble than vanillin, especially in dilute ethyl alcohol solutions. Figure 3 shows the data obtained with vanillin in glycerol solutions. It will be seen that vanillin is much less soluble in glycerol than in ethyl alcohol mixtures. Kot only is the solubility low in low concentrations of glycerol and a t low temperatures, but it does not show the sudden rise experienced with vanillin in ethyl alcohol solutions a t higher temperatures and concentrations of ethyl alcohol. The highest value obtained in this series of curves is 11.4 grams per 100 cc. of solution, compared to 76.7 grams in the case of the ethyl alcohol solutions. Figure 4 shows the data with coumarin in glycerol solutions. Again the solubility is much lower than in the ethyl alcohol solutions. Here the maximum solubility found was 1.68 grams per 100 cc. of solution while the corresponding value for ethyl alcohol solutions was 94.9 grams. LITERATURE CITED (1) De Groote, A I . , Am. Perfumer, 15, 372 (1920). (2) Mange, C. E , and Ehler, O.,IND. Eso. CHEX, 16, 1258 (1921). RECEIVED January
4, 1932.
Structure of Asbestos A n X-Ray Study B. E. WARREN,Department of Physics, Massachusetts Institute of Technology, Cambridge, Mass.
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OIVIMERCIAL asbestos comprises the fibrous varieties of the amphibole and serpentine groups of silicates. Because of its unique physical properties, asbestos is one of the most important minerals in the world. During the last three years the x-ray study of the various forms of asbestos has led to a complete determination of the crystalline structure of this group of substances and to an understanding of their physical properties. It is the purpose of this paper t o describe briefly the results of the x-ray study of the asbestos compounds, and to show how the fibrous nature of the material and the strength and flexibility of the fibers is now readily understood in terms of the crystalline structure. The work to be described has been carried out by the author and his collaborators and has been published from time t o time in a series of articles in the Zeitschrift fair Kristallographie (in English). For any of the details involved in the x-ray analysis, reference should be made t o these papers. The methods and principles involved in the x-ray analysis of complex structures are too specialized and techcical to be considered here in any detail. Accordingly, a schematic indication of the methods employed and the more interesting discussion of the results of,the analyses will be given.
DETERMIXATION OF CRYSTAL STRUCTURE A crystalline substance is characterized by an orderly arrangement of the atoms in which some small group or configuration of atoms repeats itself a t regular intervals in various directions throughout space. This smallest unit of pattern which, by repeating itself throughout space, makes up the crystal is known as the unit cell. The unit cell may contain anywhere from one to several hundred atoms, and the x-ray analysis of a crystal structure consists in determining the size and shape of the unit cell and the arrangement of the atoms within that cell. Figure 1 is a tn-o-dimensional representation of the repeating arrangement of the atoms in a crystal. The circles, triangles, and squares may represent three different kinds of atoms. The group of atoms contained in the parallelogram, ABCD, represents the unit cell, and it is readily seen that the crystal as a whole is made up by regular repetition of this unit cell. In an actual crystal the unit cell is, of course, repeated millions of times. The axes in a crystal are the shortest distances of repetition or, what is the same thing, the edges of the unit cell. In the two-dimensional case A B and A D would be the two axial lengths.
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The analysis of crystal structures by means of x-rays is dependent on the fact that the axial lengths are of the same order of magnitude as the wave length of x-rays, so that, when a beam of x-rays passes through a crystal, diffracted beams are produced. X-rays are electric waves whollv similar to light, except that the wave length is much shorter. Considering a train of water waves on the s u r f a c e of a pond, there is a success i o n of c r e s t s a n d troughs, and by the wave length of these water waves is meant simply the d i s t a n c e from one crest to the A n next. B y t h e wave A -5 l e n g t h of x - r a y s is FIGURE 1. T w 0 -D I M E N S I o K A L meant t h e d i s t a n c e REPRESENTATION OF THE REPEATING ARRANGEMENT OF ATOMSIN A from one electric crest to the next. CRYSTAL T o indicate in a rough way how the structure of a crystal is worked out from x-ray diffraction, the imaginary case of a one-dimensional crystal will be considered, that is, one in which the unit cell repeats itself in only one direction rather than in three. I n Figure 2, ABCDE represents the one-dimensional crystal, the unit cell repeating itself a t distances AB, BC, CD, etc. This crystal is in the path of the incident x-ray beam directed from left to right. Part of this beam passes directly through the crystal and produces the black spot, 0, on a photographic plate situated behind the crystal. Another part of the incident beam is diffracted by the crystal; that is, each atom in the crystal scatters the incident beam and acts as a source of secondary waves, these various secondary waves moving out in all directions from the various atoms. When two sets of water waves on the surface of a pond
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cross each other, it is evident that, a t those points on the surface where the two individual waves are a t a crest, the motion of the water will be greatest, while a t other points on the surface, where one set of waves has a crest and the other a trough, the two displacements tend to cancel each other, and the motion of the water will be small. These same interference effects are produced by the individual x-ray waves coming from atoms A, B, C, etc., in the crystal, and is known as diflraction. At most points on the photographic plate, no x-ray beam will act because the individual waves from A, B, C, etc., cancel each other; that is, the wave from one atom will be a t a crest while that from another will be a t a trough. However, in a certain few directions an intense diffracted x-ray beam will appear. One of these directions is shown in Figure 2h and is seen to be such a direction that a t any position along the diffracted beam the individual waves are all cooperating; that is, all are a t crests or all a t troughs. In those few directions in which these special conditions obtain, strong diffracted b e a m s will b e produced, and black spots will be found on the photographic p l a t e where t h e s e diffracted beams imW pinge. Fromthe posi- FIGURE 3. sILICOX-oXYGEX CHAINS a.
Single ohain in diopside
tions of these diffracb. Double chain in asbestos tion mots on the Dhotographic plate, one can calculate very simply the axial lengths in the crystal, that is, the size and shape of the unit cell. The position of other atoms within the unit cell can also be determined. Let A', B', C', etc.,'represent a second set of atoms in the unit cell. Then it is evident that under the conditions represented in Figure 2b, if A ' is very close to A , the wave from A' will cooperate with A ; if A' is halfway between A and B, the waves from A', B', C', etc., will tend to cancel the waves from ABC, etc., since, when one set is a t a crest, the other will be a t a trough. This brief discussion will suffice to indicate in a rough way how the crystal structure is determined. An x-ray beam is sent through the crystalline material, and a set of diffraction spots is produced on a photographic plate properly situated. From the positions of these spots the size and shape of the unit cell of the crystal can be calculated directly, and from the intensity of the spots, the arrangement of the atoms within the unit cell.
RESULTSOF X-RAY ANALYSES DIOPSIDE.The key to the crystalline structure of the asbestos minerals was the crystal diopside, CaMg(SiO&. This substance occurs in large well-formed single crystals and lends itself readily to a careful x-ray study. From a set of quantitative measurements of the intensity of the various diffracted x-ray beams, it was possible to work out completely the crystalline structure 15). The crysJal is monocli2ic with axial lengths, a = 9.71 A., b = 8.89 A., c = 5.24 A., P = 1 74" 10' (1 A. = loo,ooo,oco cm.). The unit cell contains four U molecules of CaMg(SiO&. The feature of particular interest b. in the structure is the arrangement of silicon and oxygen atoms. FIGURE 2. ONE-DIMENSIONAL REPRESENTATION OF X-RAY Each silicon atom is surrounded tetrahedrally by four DIFFRACTION BY A CRYSTAL oxygens, the oxygens being a t the four corners of a regular b shows the codperation of individual waves from various atoms
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weak lateral binding and a possibility of slip, however, being somewhat more evident in the structure of chrysotile than in that of the amphiboles. MICA. Another mineral of great commercial importance because of its unique physical properties is the silicate mica, occurring in flat sheets readily separated and quite flexible. The crystal structure of the mica group has been worked out ( 2 ) and now provides a very simple explanation for the interesting flaky habit of this group of minerals. The crystal structure of mica is very closely related to the amphiboles, the relation being such that mica could well be called “twodimensional asbestos.” I n Figure 3 it was seen how the strong double silicon-oxygen chain of the asbestos group was produced by joining together two diopside chains. Obviously this process could be continued and a third and fourth chain joined on, etc. By this process a continuous sheet, such as that represented in Figure 7, could be built up. The relation of the mica sheet to the asbestos chain is shown by outlining more heavily that part of the sheet which comprises one chain. Each silicon atom is still surrounded by four oxygens, but in each tetrahedral group three of the oxygens are now shared with neighboring groups. The strong silicon-to-oxygen bonds run continuously in both directions throughout the sheet. From x-ray a n a l y s i s it is found that the mica structure is built up from just such siliconoxygen sheets, the sheets being parallel FIGURE 6 . PROJECTION OF CHRYSOTILE STRUCTURE PERto o n e a n o t h e r and PENDICULAR TO C AXIS held together rather weakly by layers of The heavy linw connecting silicon to oxygen outline the magnesium, iron, and cross section of the silicon-oxygen chains which stand perpen- potassium atoms. W dicular to the plane of the paper. The atoms lie a t various These t w o examFIGURE 7. SILICON-OXYGEN SHEET AS heights above and below the plane of the paper, and thcse ples may serve as good IN MICA shown here comprise one unit cell, the length of the unit cell i._._. l l i i.s.t r~ a t i o. n s of the normal to the paper being c = 5.33 8. The chains continue remarkable progress which is now being made in the x-ray indefinitely through the structure, and only a unit length of analysis of complex substances and of the way in which their chain is contained in a unit cell. The chrysotile structure interesting physical properties can be understood very differs from that of the amphiboles only in the atoms and in simply in terms of the crystal structure, the flaky habit of the atomic grouping which binds the double chains to one mica being due to the silicon-oxygen sheets out of which it is another laterally. built, and the fibrous nature of asbestos resulting from the This lateral binding of the chains in chrysotile should be silicon-oxygen chains. much weaker than in the amphiboles owing to the fact that across sections such as A A and BB the structure is held LITERATURE CITED together by secondary forces only, not by direct valence (1) Andenon, H. V., and Clark, G. L., IXD. ESQ. CHEU., 21, 924 attractions. From the structure then the following physical (1929). properties would be expected: The substance should be (2) Pauling, L., Proc. Nat. A c a d . Sci., 16, 123 (1930); Jackson, W., fibrous and very strong along the fiber direction-fully as and West, J., Z. Krist., 76, 211 (1930). strong as the fibrous amphiboles, since the same double (3) Warren. B., I b i d . , 72, 42 (1929). silicon-oxygen chains are involved. It should be finely (4) Warren, B., Ibid., 72, 493 (1930). Warren, B., and Bragg, W.L., Ibid., 69, 168 (1928). fibered and the fibers should be readily separated, since the (5) (6) Warren, B., and Bragg, W. L., Ibid., 76, 201 (1930). lateral binding between the chains involves secondary forces (7) Warren, B., and hlodell, D., Ibid., 75, 161 (1930). to a large extent. Across those planes where only secondary forces act, slip will be possible, and the fibers should therefore RECEIVED October 26, 1931 be flexible. The structure, therefore, offers a complete explanation of the physical properties of chrysotile, explaining COSTINENTAL DYE ALLIANCE. The British its fibrous nature and also the fact that fibers are so very BRITISHCONFIRM flexible and readily separated. Owing to the fact that Imperial Chemical Industries, Ltd., has confirmed the report that agreement affecting the European dye market has been consecondary forces play such an important role in the structure, an cluded between them and Continental dye makers, according t o it is readily understood why single crystal fibers never develop a radiogram t o the Department of Commerce. Details of the to any appreciable size laterally, and why the material pact are not available but it is believed that it relates to allocation always occurs as bundles of parallel fibers with random of markets, excluding the United States. It, is not thought that arrangement includes price control or interchange of techorientation about the fiber axis. Most of what has been said this nical information. Since the agreement German dye prices in about the forces in chrysotile applies also to the amphibole England have increased 10 per cent and a further increase of varieties of asbestos, the role of secondary forces in producing prices by British dye makers is expected.
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