Almost without exception, the shapes of the microcrystals of a negative-type silver bromide photographic emulsion can be explained on the basis of a simple mechanism of twin-accelerated layered growth. Multiple twinning, both on parallel and nonparallel [111] crystallographic planes, is required for a full explanation, and evidence that this does occur is found. The location of particles of silver, formed by exposure to light, substantiates this hypothesis, and demonstrates the fact that intersections of the twin planes with the grain surface are preferential regions for the location of photolytic silver.

NOTES 4757TABLE I N,N-DIPHJSNYLTEIOC~B~AMATIC DEBIVATIVES OF MERCAPTANS Mercaptan Calcd. CdCd.,% Found, % for C H C H GHrSH CC&SH n-CJbSH n-CiElHlrsH pCE40CBCHk4H n-CrHuSH CCHoCHISH HOCH&H&H +CH&HrSH TwC&C~BSH CaEISH p C E 4 C m H o-NH&&SH CHsOeCCHsSH C&GCCH,CH&Hb G&WCHISH* CErO&CHSHb CH&CCH* CCHrCOCHgSH I (low 124.0 60.0 48.0 50.0 131.4 124 ( l W C 84.8 125 94.5 121.5 174.2 145.3 116.5 96.5 101.6 101.5 ( 1sO-182)c 136.2 70.85 71.58 72.80 73.35 72.17 65.97 74.72 75.20 75.20 75.20 71.23 63.76 64.74 64.73 61.11 72.60 6.32 70.75 6.71 71.59 7.40 72.52 7.70 73.63 5.48 72.17 5.53 66.02 4.95 74.87 5.36 75.44 5.36 75.25 5.36 75.22 5.04 71.53 5.02 64.14 5.43 64.80 5.43 64.50 5.13 61.02 4.93 72.91 6.14 6.70 7.41 7.59 5.51 5.66 4.94 5.40 5.48 5.44 5.32 5.23 5.33 6.43 6.14 5.01 a AJl melting points (capillary) are corrected. Elemental analysia by Micro-Tech Laboratories, Skokie, Ill. P Generous samplee of &mereaptopropionic acid and cmercaptosuccinic acid were kindly supplied by Evans Chemetics, Inc., New York, N. Y. R. L. Evans and W. M. Dehn, J. Am. Chem. Soc., 52,3645 (1930).in the presence of cyanide ion and alcohoI. Although a number of alkylating agents and unsaturated compounds have been employed as mercaptan reagents, very few were suitable under the necessary conditions. The suggested use4 of N,N-diphenylcarbamyl chloride ( I ) as a mercaptan acylating agent prompted a study of this substance. Mercaptides were found to react readily with I in the presence of cyanide ion or alcoholates and, in fact, afforded such easily purified adducts that use as a general characterizing agent for mercaptans seemed appropriate. The derivatives obtained (80-95oJo) are listed in Table I. EXPEEQdEINTALThe. mercaptans used were obtained commercially or were prepared by known procedures. The N,N-diphenylcarbamyl chloride was obtained from Eastman Organic chemicals.Preporattima of N,Ndiphmylthiocarbam& derivatives. A solution containing 0.23 g. (0.01 g.-atom) of sodium in 30 ml. of alcohol was treated with 0.01 mole of mercaptan. The solution of mercaptide was then added to B solution of 2.31 g. (0.01 mole) of N,Ndiphenylcerbamyl chloride in 20 ml. of alcohol. The solution was warmed on a steam bath for 5 min., the precipitated salt filtered, and the derivative allowed to crystallize. cooling waa sometimes necessary to induce crystallization. Recrystalhation was wily effected from alcohol. In general, the melting point was not raised after one recrystallization.The only mercaptans studied which did not d o r d derivatives in high yield were pnitrobeneyl mercaptan, @-mercaptopropionic acid, and a-mercaptosuccinic acid.Several previously unreported compounds were synthesized during preparation of a series of aminoethylpiperidines.Addition of amines' or ammonia10 to 2-or 4 vinylpyridine gave aminoethylpyridines which were catalytically reduced to piperidines.An attempt to pyridylethylate ammonia as described by Magnus and Levinelc gave principally bis [2-(2-pyridyl)ethyl]amine rather than 2-(2-aminoethy1)pyridine. The latter could be made b...

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The temperature dependence of the electron lifetime and of the time for decay of an internal applied electric field in the silver bromide microcrystals of a simple photographic emulsion has been measured by the technique employing flash exposure of the emulsion in pulsed electric fields. Activation energies were found to be 0.236±0.012 eV for the electron lifetime and 0.245±0.008 for the field-decay time. The agreement of the temperature dependence of the two processes, together with the observation that the room-temperature values of these two times are, without exception, nearly equal in measurements made on a variety of other emulsions, supports the hypothesis that the mechanism of permanent electron-trapping involves the motion of the silver ion to a temporarily trapped electron to form a stable center. These results are not consistent with the alternative suggestion, namely, that the electron is captured at a preexisting deep trap consisting of a silver ion associated with a crystal imperfection.

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