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Vol. 79
is represented: namely, the atomic arrangement based upon a fifty-atom tetragonal unit earlier described.2 That there exists, nevertheless, a second. and probably more cornmo~ilyobtained niodificntion of boron has seemed certain from published powder diffraction data. For example, the interplanar spacings listed4 for prominent powder lines given by a sample of better than 99% purity (unspecified method of preparation) are wholly incompatible with our tetragonal cell. Recently we 40 have obtained from independent sources two preparations of boron briefly characterized as follows: the stated purities are 99.4 and 99.570 B but the preparative chemical methods are withheld; both are aggregates of small single crystals resulting from crystallization of the melt, and both afford specimens suitable for single crystal study; and they give a common powder diagram which in0.2 0.4 0.6 08 1.0 cludes the lines listed by Godfrey and I I - a r r e r ~ . ~ 1I.F. Dr. S. Geller of the Bell Telephone Laboratories Fig. 1.-Retention of solid ethyl bromide (curve “a”) and provided us with Preparation I. Amorphous liquid ethyl bromide (curve “ b ” ) as a function of the niolar boron, supplied by Cooper Netallurgical Associates, fraction of bromine. was melted partially in a “Heliarc” furnace and alThe purpose of experiment (a) was to determine lowed to crystallize in a helium atmosphere by E. whether free organic radicals were trapped in the Corenzwit of the Bell Laboratories. Preparation solid. The constancy of the retention indicates 11, received within the fortnight, came to us from either t h a t such radicals do not exist or, t h a t they the TJiiited States Borax & Chemical Corporation react before mixing with the scavenger solution. through the good offices of Professor X.IT.LauThe reproducibility of the results obtained using bengayer. the second method of freezing bromine-ethyl broOscillation, Weissenberg, and precession photomide mixtures was checked by repeating a number graphs of single crystals-from Preparation I Desof experiments a t the same bromine concentration. tablish a rhombohedral lattice having a = 10.12A, cy S o variations beyond statistical limits were ob- G3’2S‘ ; the associated triply primitive hexagonal served, even though the freezing time varied from cell has A = 10.95, C = 23.73 A,accurate to 0.2%. 3 to 5 minutes. These preliminary results show that the drop in The experimental density, 2.35 =k 0.01 g. cc., is retention caused by the addition of small quantities equally consistent with 107 or 10s atoms within of bromine is less sharp than that observed in the rhombohedral unit. The diffraction symliquid ethyl bromide (Fig. Ib). T o clarify the metry and lack of glide plane vanishings indicate nature of the processes involved we are now carry- R s n , R32, or RXm as the space group. Spectroing out experiments t o identify the radioactive metrically measured intensity data (using both products obtained and to determine the compara- Cu Koi and 1 x 0 Kcr radiations) have been obtained tive behavior of the bromine isotopes produced by for two zones, Le., with the hexagonal A and rhombohedral a as zone axes. The statistical distri(n, y) processes. bution of intensities is centrosymmetric5 for the The author wishes to thank Professor H. Halban (Paris) for encouragement and support, t o Pro- first zone, hypercentric6 for the second, thus supfessor J. JVillard (Wisconsin) and Dr. P. F. D. Shaw porting the unique choice of R j m as the space group. 1X-e note that boron carbide’ also crystol(Oxford) for helpful discussions. lizes in R b , with a = 5.19 A, N = 63’1s’ SO that ECOLE SORMALE SUP~RIEURE LABORaTOIRE D E PHYSIQUE MIRIAMMILMAN all lattice translations are approximately half the 24, RUE LHOMOND, PARISYo, FRAKCE corresponding values in rhombohedral boron. RECEIVED AUGUST8, 1957 However, there is no suggestion in the boron data of a pseudo-unit comparable in volunle or obviously related in structure t o the boron carbide unit. XIRHOMBOHEDRAL ELEMENTAL BORON though undoubtedly belonging t o a more complex Sir: structural type, our rhombohedral boron affords The simultaneous occurrence of two widely dis- intensity data showing little or no evidence for the similar external forms for single crystals of pure presence of the large and variable concentrations of short-range defects which seem to characterize3 boron growing1 on a hot filament was for a time to reflect true structural polymorphism, all actual specimens of tetragonal boron as grown ($) T ?;. Godfrey and I 3 E . TT.arren, J . Chciu. Phys., 18, 1121 but comprehensive diffraction studies3 show that, a t least in the work cited,I a single structural type (19501 ( 5 ) E. R . Howells, D. C. Phillips and D. Rogers, Actn CYSSL.,3, ?io ( m o ) . ( I ) A . 1%’. Laubengayer, D. T . Hurd, A. E. NeFkirk and J. 1,.
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Hoard, THIS JOURNAL, 6 6 , 1924 (1943). (2) J . L. Hoard, S. Geller and R. E. Hughes, i b i d . , 73, 1892 (1951). (3) J. L. Hoard, R. E. Hughes and D. E. Sands, to be submitted to
THISJOURNAL.
(0) H . Lipson and 11,IT,Woolfson, i b i d . , 6, 080 (lQ.52). (7) H . K. Clark and J. L, Hoard, THIS J O U R X A L , 6 6 , 2115 (1943); G. S Zhdanov and N. G Sevast’yanov, Compt. rend. acad. sci. CT.R. S .SI 32, 432 (1941).
Oct. 20, 1957
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in the large thermal gradient normal t o the surface of the hot filament We are confident of success in determining the atomic arrangement in rhombohedral boron when we shall have completed the quantitative measurement of the numerous h k I intensity data. Thanks are due Dr. Gordon S. Smith and Mr. D. B. Sullenger for taking some of the photographs. (8) S o w a t Radiation Laboratory, Universlty of Callfornla, Lirermore, California.
BAKERLABORATORY OF CHEMISTRY CORNELL UNIVERSITP DOXALD E. SASDS* J. L. HOARD ITHACA,NEW YORK RECEIVEDJULY 30, 1957 THE PREMIXED OZONE-CYANOGEN FLAME1n2
Sir: The pure ozone decomposition flame to oxygen3 and the premixed ozone-hydrogen flame4 were recently described. A premixed pure ozone flame with a carbon compvund, namely, cyanogen, has now been achieved. It was first established, in static experiments, that cyanogen and pure ozone can be mixed and stored for a considerable time without reaction. Thus the mixture 3(CN)2 4 0 3was kept in a 100% 0 ATOMS [ O F TOTAL NUMBER OF ATOMS P R E S E N T ] , cc. Pyrex vessel, a t 1000 mm. at 0' for 2.0 hours Fig. 1.-Burning velocities of 0 8 (CN)? and 0 2 with no noticeable change in pressure; after this (CN)Z mixtures ( a t 0" initial gas temperature and 1 atm.). time cyanogen was frozen out at -78", the 0 3 All flames on the (CN)z-rich side up to and inpumped off and the volumes of the separated gases N t burn were found to be essentially equal to their original cluding the mixture burning to 2CO volumes. Identical results were obtained with uniformly, noiselessly, as brightly as an electric arc 0 3 and with a pink-violet color. The 2(CN)2 the mixture 3(CN)2 203. The results of our laminar flame measurements flame is particularly bright and has a different are given in Fig. 1 and compared with 02. Burn- characteristic blue green color. Their temperatures can be calculated6 with great ing velocities of (CN)2-03mixtures containing 2.5.0, 33.3, 40.0 and 100.0 mole % 0 3 were, respec- accuracy ( + 2'K.) ; one of them is compared with 3, 242 12, 285 =t G and 420 + 6 the corresponding O2flame's8 below tively, 60 cmjsec. A mixture beyond the stoichiometric 7 0 D . - - Gas 1.o 10.0 point, on the Oa-rich side, containing 50.0 atom 7 0 composition Atm. Atm. 0 detonated immediately upon ignition. The (CX), On 4850 5025 same apparatus was used as in the 03-Hz measure3(CX)* 4- 20, 5208 3506 m e n t ~ ~the ; desired mixture was stored over water in a Pyrex gas holder, dried by passing through a In these calculations the value of AIIfZ5Ofor ozone trap cooled t o -19'. (H20-content of gas = = 3-33.98. and for cyanogen = +73.85 kcal.,'mole 0.11 mole yo)and ignited by a hot Pt-wire from an was used. aluminum burner tip ( i d . = O.6G nini.). Since (F) Acknowledgment is made t o t h e Reaction Motors, Inc., and flame velocities of (CN)2-0z flames are increased t o Mrs. Marianne Stoltenberg for their help n i t h some of the calculaby traces of H20,jwe used the same apparatus and tions. (7) J. B. Conway, R. H. Wilson, Jr., and A. V. Grosse, THISJ O U R the same conditions t o measure (CN)2-0zflames. 76, 409 (1953). The shapes of the three O3 flames described are NAL, ( 8 ) J. B. Conway, W. F.R . Smith, W. J. Liddell and A. V. Grosse, widely d i f f e r e r ~ t . ~Although .~ the Os-rich side of ibid., 77, 2026 (19%). the Oa-H2 and (CN)z-03 systems could not be ex- THERESEARCHISSTITUTE A. G . STRETG plored due t o their detonability, it is unlikely that OF TEMPLE USIVERSITY -1, 1'. GROSSE 44, P.4. the latter system will show the high peak of the PHILADELPHIA RECEIVED XVGUST 26, 1957 03-H~system. -111 (CI%),-03 mixtures burn comparatively slowly and even a t the 2CO+N2 ( k , = 33.3 atom % 0) point, the velocity is substanDERIVATIVES OF I-THIA-4,s-DIAZACYCLOHEPTAtially below that of pure ozone. 2,4,6-TRIENE. 111. CORRECTIONS AND ADDENDUM
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(1) Paper presented a t t h e Sixteenth International Congress on Pure and Applied Chemistry, Paris, France, July 18-24, 1957. (2) This research was supported by t h e United States Air Force through t h e Air Force Office'of Scientific Research of t h e Air Research and Development Command under Contract h-0. AF-l8(600)-1175. ( 3 ) .4. G. Streng and .'I v. Grosse, THISJ O u R N n r . . 79, 1317 (1957). (1)A. G. Streni: and h 1'. Grosse, ibid., 7 9 , in press (1057). ( 5 ) 12. S. Prokaw and I
