June. 1926
I S D C S T R I A L ,450 EXGINEERISG CHEMISTRY
includes white ash, pignut hickory, red ‘alder, red mulberry, sugar maple, and catalpa; Group B (with high extractives in the heartwood) includes yellow poplar, yellow birch, white oak, red oak, locust, and eucalyptus. Conclusions
1-In softwoods the water, ether, and alkali extracts are higher in the heartwood than in the sapwood, and the cellulose and lignin are correspondingly lower in the heartwood
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(except in white spruce, in which cellulose-lignin content is approximately the same in the two bands of growth). 2-On the basis of water, ether, and alkali extractives, hardwoods are divided into two groups: (a) those with high extractives in the sapwood, and ( b ) those with high extractives in the heartwood. The former have low cellulose in the sapwood, the latter low cellulose in the heartwood. 3-Acetic acid by hydrolysis is higher in the sapwood than in the heartwood of all the woods.
Industry Finds a New Tool-X-Rays By D. H. Killeffer, Associate Editor
The discoz‘ery of the X - r a y has opened the door to vast stores of industrially important facts. Already’it i s reziolutzonizing the metallurgical industry and as our knowledge of X - r a y technic iucreases new wonders are being recealed in other jields. NDUSTRP usually looks, to its own hurt, with disdainful indifference upon the newest advances of what it considers “high brow” pure science until its operations are revolutionized by the application of some newly discovered principle or method. Each year, each month, almost each day, sees some advance of pure science put into the overalls of industry. The scientific oddity of yesterday becomes the foundation of tomorrow’s practice. Science and scientists repeatedly prove the truth of that and industry teems with illuminating illustrations. Yet it is one thing to prove and t o illustrate, and quite another to realize in practice a point of view so obviously axiomatic. So it has been with X-rays. How distant seem the experiments of Roentgen leading to the discovery of a new kind of radiation, which for want of a better name he called X-rays, from the hardening of steel, the sealing of an envelope, the multitudes of catalytic reactions, and the vastly important problems of corrosion. Yet in the scientific toy of a very few years ago-few of us fail to recall with what awe and wonder we first beheld the bones in our own hands in the fluoroscopic screen of a side showhas been found the key to vast stores of industrially important facts about diverse kinds of matter. Already our theories of the haraening of steel and the ductility of metals have undergone a complete revolution and our preconceived ideas of colloids, crystalloids, and amorphous matter are being materially modified as the result of the use of this new tool. Only a beginning has been made and no one’s imagination is yet equal to the task of foreseeing the possible end. Already industry has taken profitable cognizance of this apparently purely theoretical advance and has made it its own.
I
s
Properties of X-Rays
X-rays were discovered by their ability to penetrate matter opaque t o visible light. They could be made to affect a photographic plate through the human body and to reveal in bold outline its parts of different opacity to them. Bones, fractures, and foreign materials of any kind within the human body could be discerned as if the surrounding tissues were rendered invisible. One might even imagine that the tellers of fairy tales foresaw such a thing when they conferred upon their characters the ability to render themselves invisible. This phenomenon of selective absorption of X-rays has become of the greatest practical importance, particularly in the field of metallurgy where minute flaws in castings may have serious effects on their usefulness. Rays of greater and greater penetrative poner have finally made it quite an ordi-
nary thing for an investigator to outline accurately voids one or two millimeters in dimensions in blocks of steel a decimeter thick without altering the steel in the least. Tt is thus possible to detect minute flaws in the interior of castings whose value would have to be destroyed to render any other method of test applicable. Study of Castings
Industry moves forward as fast as it is supplied with the minutiae of its operation and no faster. For instance, the widening use of very high pressure superheated steam for power and of high-temperature and high-pressure cracking processes in refining petroleum has brought into prominence defects in cast-steel valves and pipe fittings not hitherto important. The casting of pipe fittings from steel has been considered a comparatively simple thing for the reason that strains in use have seldom been sufficiently great to give them a real test. However, under the severity of the newer types of service even very slight flaws soon showed themselves and often led to disastrous results. To correct this, careful studies of all parts of such castings by X-ray methods were made and casting practice improved to correct the defects found. The result has been a vast improvement in the quality and service of the finished fittings. Such methods had previously been applied with great success to the casting of cannon, their carriages, and other gross objects cast of steel. Study of Atomic and Molecular Structure
This kind of thing has proved very valuable to industry, but when compared with the possibilities in the study of so vast a field as atomic and molecular structure its importance is greatly overshadowed. In 1912, Von Laue in Germany and Bragg in England began the publication of a series of papers dealing with the ability of X-rays to be deflected, reflected or, perhaps better, refracted when passed through crystal substances. Basing their experiments on the analogy to the diffraction spectra produced by passing visible light through fine gratings, these investigators passed X-ray beams through crystals in various orientations and found that the deflected beams showed distinct maxima and minima as the crystal was rotated and that the angles of deflection were quite definitely properties of the internal structure of the crystal. Other investigators mere attracted to the field thus opened, and fact has been piled upon fact until in the hands of a skilled worker this technic will now reveal far more about the infinitesimal structure of inatter than was ever conceived
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INDUSTRIAL AND ENCJINEEIZING CIfEJllSTllY
Vol. 18, No. 6
possible hefox-quite as much, indeed, as had been irnagineil. parently increased if a smaller atom is introduced into tile So accurately can the spacings of atoms in a crystal be de- lattice of a larger one. Where intermetallic compounds exist termined in this way t,hat we may almost say that they the properties of the alloy are fundamentally altered but are rendered vkihlc and tangible. tlicir presence is easily dotected. Two general types of technic have been developed. T h o Industrial Chemical Applications at M . I. T. Laue method depends upon the diffraction of a pinhole beam of X-rays of various wave lengths by a single crystal The metallurgicsl applications of X-ray technic are atvariously oriented, and the powder method utilizes a mono- tracting the attention of many investigators, hut for our pres. cliromatic beam--i. e., a beam of rays as nearly as possible ent purposes more strictly chemical applications arc probably of a single wave length--from a slit and crystal powder in more interesting. They are certainly newer, as inany of the which there is opportunity for particles in every possible investigations to be mentioned below are still unfinished. orientation. Tlic deflected beam may bo recorded on a For information about them the writer is indebted to the photographic film for subsequent accurate measurement Researcli 1,ahorat.ory of Applied Chemistry of the Massaor it may he passed into a goniometric ionization chamber chusetts Institute of Technology, the pioneer in indust,rial by which the angular deflection is easily determined. Many cbemical applications of this newest of research tools. Work modifications of these methods are in use varying in detail upon them is being vigorously prosecuted in this institut,ion, and slightly in principle. wlicre complete resources for this type of thing are available. Tlic use of diffraction patterns and the data deduced from Commercial materials, in particular, are being subjected to them is far more interesting for the moment. Metals ordi- X-ray investigation and tlic heariiig of their infinitesimal narily crystallize in tho cubic system, which is the siinplest st.ructures on their practical properties determined. The existence of strains in metals and of preferred orient,aof all and hence, so far, the most careiully studied. From an X-ray diffraction pattern it is easily possible to determine tions of crystals that might lead to lines and planes of cleavage the exact positions in space of each of the atoms making up are far more readily detected by examination of the inmetallic crystals. Each metal has its own characteristic finitesimal structure than by any other means yet devised. spacings arid thus it is possible easily to determine what A steel casting whose struct.ure appears to be perfectly metals are present in a mixture. If two metals are present uniform under the microscope may show decided strain lines as such, the diffraction pattern will show two series of char- when subjected to X-ray examination. In this way it is exacteristic lines, but if they should be in a completely homo- pected to reach methods oi casting and annealing of a pergeneous solid solution only one series of lines would show. ieotion hitherto impossible, and perhaps on this account it I n the simplest cases these linea are intermediate between the will be possible so to improve metal parts as to make conpositions of those of the metals composing the solution. siderable savings in the amount of metal necessary to give a Froin the relative displacement of these lines it is easy to reach particular strength and perform a particular task. That the internal structure of metals is intimately related a close approximation to the constitution of the mixture. If the two metals form an intermetallic compound, an entirely to their strength characteristics is obvious, and thus the new set of lines characteristic of that compound will be more accurate determination of this by means of X-rays found. Rv no other method is i t possible to determine conclusively whether compounds between the metals exist or not. This technic is leading to very important facts as to the nature of alloys and tlie reasons for their changes properties with changes in composition. For instance, it has been found that ductile metals, generally, crystallize in the form of what arc called face-centered cubes; that is, each unit cube is made up of stoins arranged at the corners of the cube and in tlie centers of its faces. This unit structure is re p e a t e d t h r o u g h o u t the crystal. Nonductile metals, generally, are to be found in the form of bodycentered cubes; that is, the unit cube consists of atoms arranged at the corners and the center of a cube. It is the change between theqe two Forms, and otliers somewhat different that are present in some metals, that appears to cause the remarka b l e p r o p e r t i e s of some alloys. Each atom appears to possess a very definite space charactoristic of Goniomemlc lonlratlon Chamber for X-RPj its own and if a small amount of a Measurements larger at.om is introduced into the space lattice of a smaller one, rigidity res.&, whereas ductility is ap-
I.VD US'TRIAL A N D ICNGI NBI312I NG CI1B.W STh: Y
.Tunc, 1926
crystal lattice, while tire satisfactory piece had its oxide in segregations. In a similar manner it is possible to detect the lines characteristic of iron oxide in extremely low concentration in the metal. On the other hand, if one has a mixture such as sodium chloride and potassium bromide which it is quite impossible to analyze by other methods, it is quite easy to say whether the bromine is combined with the sodium or with the PO-
(1) (1)
i1ithert.o unexpected practical results. Plaster of I'aris and lime cements have been mentioned. In a similar way it has been possible to determine with great accuracy the extent of polymerization of a number of materials ordinarily considered amorphous. The polymerization of certain resins can be measured in this way. It is hoped, too, that these methods may throw some light upon tlic plienoinenon of adhesion, about which we now know practically nothing. The pos-
(8)
(2)
cast Steel As cast. Large ciysttai~,preferred oriciitstiori and rtraio. (2) Normal commercial * m i e l i i n ~practice. with no orientzition or strain.
tassium or with both, for thc dimensions characteristic of the atoms involved are easily measured. Of course, no one would ordinarily care which way such a mixture was made up, but there are similar analytical dilemmas that are important and may be resolved in such a manner. For instance, the are the complex silicates known under the generic name "asbestos." The use of asbestos as a support for the platinum catalyst in the contact mass in a sulfuric plant makes it essential that the particular material used stand up under the conditions there met. At present there is no way known of determining this except that of trial and error. Now it is casily possible to decide just what crystal sorts are present in any specimen of asbestos by means of the X-ray and, once having doternlined the preferred substances which good asbestos should contain, it will not be difficult to sta e beforehand on the basis of X-ray evidence whether or not narticular samule is Rood.
579
(3) Ideal structure.smal1 equiaaial cryMls
sibility that glue and certain other colloidal substances may reveal that their property of adhesion is due not to their lack of structure, but rather to their possible ability to accept the structure of the materials to which they are applied. is being carefully investigated by X-ray technic and with considerable hope of success. Already it has been possible to outline a definite structure for cellulose which probably will have important bearings on a number of diverse important affairs. So far this discussion of chemical applications of X-rays has considered work completed or in progress a t the Massachusetts Institute of Technology. It is not to be presumed from this that no other laboratories are similarly engaged. ad and in America numbers of able investigators rrying on fundamental re IC, but in general these are b c than essentially industrial in
..
may be solved, by a knowledge of the infiniTransformer Steel-Same Comp(r*ition, Uilfeerences io Annealing (I)Inferlor (2) Excellent tesimal structure of thematerial. I n a similar way it has been found that an optimum particle size exists for the plasticity of lime cements and Other Applications mortars, which if taken into account inay lead to extremely The X-ray has given us a means for measurement of a numvaluable results in the use of such materials. The determination of ultimate particle size in any material ber nf physical constants with extreme accuracy and with may he readily accomplished by X-ray methods and leads to much greater facility than other methods allowed. When
1S D U8TM.4L .4 N 1 ) E.VGILV8hXI.VG CHEMISTRY
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tungsten is to be drawn into filaments for electric lamps of such exireme fincness that their diameters fall well within the limit of error of ordinary measuring methods, the densit,y nf the metal becomes of extreme imnortanco
shown that the number of carbon atoms in a chain compound-X-ray methods have shown that chain coinnounds are actual chainlike
Vol. 18, So. 6
work in this field is confined to a very few investigators, of wlmni the majority are devoting themselves to mctallnrgical problems as thesc offer the greatest hope of quick and prac-
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