THE CHEMICAL WORLD THIS WEEK
Young Chemists Get α Hearing, Prize Paper Wins Free IM. Y. Trip C&EN REPORTS:
Pittsburgh Section M e e t i n g - m - M i n i a t u r e
PITTSBURGH.-In order to provide experience in the presentation of papers before scientific groups and in hopes of improving the standards of such presen tation, the Pittsburgh section of the AMERICAN
CHEMICAL
SOCIETY
held
its
first meeting-in-minidture on June 14 and restricted the program to junior scien tists in industrial laboratories, and gradu ate students. To encourage the best pos sible presentations, an award ot a tree trip to the national ACS meeting in NewYork this fall was offered for the best paper submitted. The prize winner was Lloyd Barkley of the University of Pitts burgh who described a series of reactions of fluorine compounds which indicated that the hydrogen atoms on t h e methylene group alpha to a trifluoromethyl group behave in an anomalous fashion. Honor able mentions were a w a r d e d to Chester Crelecki of Duquesne University, S. Allen Heininger of Carnegie Tech, and Robert Palchak of Pitt. At t h e dinner that followed the tech nical sessions the young speakers were informally reminded of the necessity of addressing the microphone directly, pre paring attractive slides with ample sized lettering and a minimum of data, and given other pointers on effective oral presentation. Adsorption of Cracking Catalysts Saturated and unsaturated hydrocar bons are adsorbed on the surface of a cracking catalyst by different mechanisms, Speaker of the evening \V. Conard Fernelius, Penn State, discussed coordi nation compounds and their applications at the Pittsburgh Section dinner meeting
according t o a paper presented at the meeting by JR. G. Zabor of Mellon Insti tute. T h e saturated compounds, Zabor said, do not chemisorb but arc associated with the catalyst b y physical adsorption up to about 150° C. Above that tempera ture they do not seem to adsorb at all in any appreciable amount. Consequently, if the cracking of these materials is as sumed to occur through the formation of carbonium ions, then the rate controlling step of t h e process must be t h e formation of the carbonium ions on the catalyst, since they will be desorbed immediately upon formation. Unsaturated hydrocarbons, according to Zabor, chemisorb readily at the cracking temperature a n d even at lower tempera tures. From -this data it may be assumed, according to the speaker, that the rate of cracking of olefins is determined b y the rate at whicri the carbonium ions formed on the catalyst surface are decomposed and subsequently desorbed. A key to better performance from cracking catalysts was suggested in a presentation by George E . Elliott, J r . , of Gulf Research who re ported u n u s u a l promise in calcium-magnesiurn-silicat^ catalysts in yielding high ratios of gasoline t o gas-plus coke, and in producing gasoline having a high per centage of unsaturates. The catalysts used in the work reported were produced by partially substituting
magnesium for calcium in a calcium sili cate precipitate. Various compositions ranging from 1 to 3 8 % C a O and 30 to r 0 /e MgO were prepared. T h e speaker reported that increasing magnesium con tent increased cracking activity, density, surface area, and thermal stability. How ever, resistance to decomposition by steam was reduced. Cracking activity could b e further enhanced, according to Elliott, by treating the catalyst with saturated steam up to temperatures of about 600° C. This improvement was apparently effected by an increase in the surface area of the material and a further conversion to the active sepiolite structure. A method for predetermining the sta bility of complex compounds when the classical dissociation constants are of little value was suggested by G e r a l d Hansen of Hall Laboratories. T h e method alsodefines a relationship between the B o h r atomic radius, the internuclear distance as determined b y x-ray diffraction data, and the dissociation potential of a diatomic system which will permit the determina tion of any one of these values if the o t h e r two are known. Hansen's system revolves upon the premise that an electron being shared by two nuclei cannot have a statistical posi tion on the line of centers between t h e two nuclei. T h e amount of this displace ment from t h e line of centers was cal culated b y a vector resolution of t h e forces acting between the atoms and found to give a value which closely approximated the product of the dissociation potential in electrostatic units and Planck's constant divided by t h e electronic charge in elec trostatic units.
Vapor Reaction Technique Gives Transparent Television Screens C & E N REPORTS: A m e r i c a n Physical S o c i e t y M e e t i n g
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SCHENECTADY, N. Y . - B y forming phosphor materials directly on the cathode ray tube scre-en from reactants in the va por phase, General Electric scientists have found that t h e y can produce a transparent luminescent screen. L. R. Koller told the American Physical Society summer meet ing held here, June 14 to 16 that he and his colleagues h a v e formed such screens by vaporizing manganese chloride and metal lic zinc in an atmosphere oi hydrogen sul fide. The product of the vapor phase re action, a magnesium-activated, zinc sulfide phosphor w a s precipitated directly on the relatively cool glass surface in the sub limation chamber. Pressures in the range of one to four millimeters of meioury ab solute were used with maximum tempera tures of a b o u t 550° C. dictated by the softening point of t h e glass screen. T h e thickness of t h e films was determined bv
CHFMICAL
the time the reaction was permitted to continue. However, one micron films seem to give satisfactory performance. Penetration of 10 kv. electrons into such films was determined to be about 2.4 microns. T h e authors reported that no study had been made of the crystallographic state of the films but predicted that they were a microcrystalline formation. O t h e r types oi phosphors have been made but t h e yellow luminescing, manganese-activated zinc sul fide has given the be rformance. No pure white image has . . b e e n attained. Internal reflections between t h e particles of t h e phosphor are also eliminated so that there is no halo around the irradiated area and the definition of the image is im proved. T h e largest sized screens made in the present laboratory study h a v e been 12 inches in diameter. For larger sizes, the
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Crystals G r o w as Kelices N e w microscopic techniques have re vealed conclusively that crystals d o not g r o w layer after layer as has b e e n gen erally assumed since the days of Willard G i b b s , b u t generate continuously as a helix, P. C. F r a n k of the University of Bristol told the meeting. T h e first d o u b t was cast on the old theory by experiments that revealed that crystals would grow in atmospheres with as little as \c/c supersaturation while the equilibrium energies of t h e theory required as m u c h as 5 0 % supersaturation. Frank said that it was then d e c i d e d that the Gibbs theory ap plied only to perfect crystals w h i c h very seldom occur in nature. Most crystals h a v e dislocations which result in the over lapping of lattice layers at some part of t h e lattice. Such an overlap w o u l d pro vide a fresh e d g e on which the crystal could grow continuously. T h e growth front would pivot around the end or ends of the overlap, producing a spiral con figuration. T h e curvature of the spiral will b e determined by the critical curva ture determined u n d e r the old theory· This theory is supported by earlier ob servations that crystal faces advance in t h e shape of a very flat cone rather than as a p l a n e . Electron micrographs m a d e by s h a d o w i n g now actually show t h e step wise pyramids which comprise these sur faces. Frank also showed some photo micrographs m a d e with t h e recently per fected phase, light microscope which re veals this structure very convincingly. A n e w area of x-ray research in the 5 0 to 100 m.e.v. range is b e c o m i n g active as high energy accelerators b e c o m e fairly common throughout the country, accord ing to George Baldwin of General Elec tric. H e said that one of t h e major diffi culties in this work is t h e determination of the actual energy of the particles in volved since t h e usual x-ray monochromators are not effective at t h e very small w a v e lengths of the high energy beams. O n e point that has been cleared up re cently, h e s;>id, has been the proof that in the resonance absorption of x-rays it is a single nucleide which is energized inde p e n d e n t of the remainder of the nucleus. The4 linear accelerator, which may ulti mately play a part in the high energyx-ray work, has already foimd ample ap plications for its special abilities accord ing to \V. K. Panofsky, who reported on the work at the Universitv of California which has one of the few such machines in existence. He said that t h e small b e a m diameter, high current, and precision of b e a m integration possible with the linear accelerator have proved ideal for p r o d u c ing high specific activities in isotopes for chemical investigations. It has also m a d e possible the addition of m a n y new isotopes to those already known, especially for t h e lighter elements. V O L U M E
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StatutIT -mi
»
JUNE
2 5,
1951
Products
BHC (Benzene Hexachloride) Borax Boric Acid Boron Trichloride Carbon Bisulphide Carbon Tetrachloride Caustic Soda Chlordane Chlorine Citric Acid DDT (Dichloro Diphenyl Trichloroethane) Ethylene Trithiocarbonate Silicon Tetrachloride Sodium Hydrosulphide Sulphur—Specially processed for all industrial and agri cultural uses Sulphui—Insoluble (for rubber compounding and other uses) Sulphur Chloride Sulphuric A c i d Tartaric A c i d Textile Stripper Titanium Tetrachloride Toxaphene (Chlorinated Camphene)
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