June 8, 1905] 



NA TURE 



141 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, March 30. — " The Theory of Photographic 

 Processes, Part ii. On the Chemical Dynamics of De- 

 velopment, including the Microscopy of the Image." By 

 S. E. Sheppard and C. E. K. Mees. Communicated by 

 Sir William Ramsay, K.C.B., F.R.S. 



This paper forms a continuation of a preceding one on 

 the kinetics of development {Proc, Ixxiv. pp. 447-473). 

 By microscopical methods, the growth in the thickness of 

 the reduced layer of silver particles, in their size and their 

 number, under varying conditions of e.xposure and develop- 

 ment, has been studied. For the structure of the developed 

 negative the following facts were ascertained : — 



(a) With constant development for a short time the 

 depth of the image is independent of the exposure. 



(6) With increased time the depth increases very rapidly 

 at first, reaching a maximum for each exposure, after 

 which it is constant, while the density of reduced silver 

 still increases. 



(c) With long development the depth increases some- 

 what with the exposure, a limit naturally being fixed by 

 that of the film. 



Sise of the Grain. — This increases with the time of 

 development, the rate being a function of the exposure, 

 but the limiting size independent of this, and fixed by the 

 original haloid grain. Thus in the early stages of develop- 

 ment the size of the grain increases with exposure, but 

 on ultimate development is independent of it. 



Soluble bromides at moderate concentration give a 

 smaller grain for the same time of development, but de- 

 pending on the exposure. On ultimate development the 

 size becomes the same. 



Number of Grains Reduced. — In the surface-area the 

 number is independent of the exposure, but in the volume 

 unit for moderately long development the number increases 

 with the exposure, and is nearly proportional to the density. 

 It increases rapidly with the time of development, more 

 so than the density, and soon reaches a maximum. 



When plates are exposed through the glass side, the 

 thickness of the reduced layer is much the same, but the 

 numbers less. Further, the grains nearer the glass are 

 larger, showing that the more exposed grains start develop- 

 ment first. Generally, each grain develops as an isolated 

 system, only uniting to form " aggregates " when the 

 packing is close, as in high exposures. The true reaction- 

 layer is in the gelatin skin surrounding the grain, its 

 thickness being of the order 00005 mm., and the reaction 

 is similar to the catalysis of HjG^ by colloidal metals, with 

 convection excluded. 



Early Stages of Development. — From considerations of 

 the order of reactions the validity of the Watkins factorial 

 method of development is discussed, and the ** time of 

 appearance " shown to be a measure of the development- 

 velocity for the initial stage of development. For ferrous 

 oxalate this initial velocity is shown to be proportional to 

 the concentration. 



Effect of temperature for ferrous oxalate can be repre- 

 sented by the formula of van 't Hoff, log K=— A/T-l-C, 

 but the temperature-coefficient for 10°, K+io°/K, varies 

 for different developers and emulsions, and cannot serve 

 as a criterion for distinguishing rate of chemical action 

 from diffusion in development. 



It is further shown that " tanning " the film with 

 formalin does not alter the development-velocity. 



For the " penetration " of the developer, it was found 

 that with plates exposed from the back the image appeared 

 on the glass or film side first according to the exposure. 

 This is explained by consideration of the micro-structure 

 of the exposed film, and the conclusion is again obtained 

 that the " re-activity " or readiness to start development 

 of the individual grain is a steady function of the ex- 

 posure. 



From the absolute " time of appearance " of the image 

 at the back it is concluded that the diffusion-induction is 

 not great, especially since other considerations show that 

 in the early stages of development the chemical reaction 

 has more influence than diffusion. 



NO. 1858, VO-L. 72] 



Chemical Society, May 17.— Prof. R. Meldola, F.R.S. , 

 president, in the chair. — The desmotropic form of sub- 

 stances of the ethyl acetoacetate typo in the homogeneous 

 state and dissolved in neutral media : J. W. Brtihl and 

 H. Schroder. The authors claim to have established by 

 optical measurements with solutions in various media that 

 both the ethyl acetoacetates and their secondary and 

 tertiary alkyl derivatives, and also the camphorcarboxylic 

 esters and their alkyl derivatives, display a pure uniform 

 ketonic structure, and are free from the enolic forms. — ■ 

 The chlorination of methyl derivatives of pyridine, part i., 

 2-methylpyridine : W. J. Sell. The compound CjHCljN 

 was obtained by chlorinating 2-methylpyridino in hydro- 

 chloric acid solution. — The absorption spectra of uric acid, 

 murexide, and the ureides, in relation to colour and their 

 chemical structure : W. N. Hartley. The ureides, 

 diureides, and some oxypurin derivatives are divided by 

 the characters of their absorption spectra into two groups, 

 the oximino-ketones with no ethylenic linking associated 

 with the carbonyl groups, and the substances which have 

 one or more such Unkings. — Observations on chemical 

 structure and physical properties associated with the theory 

 of colour : W. N. Hartley. The main feature in a 

 coloured substance is the occurrence in two parts of the 

 molecule of ethylenic and benzenoid groupings and of 

 ketonic groupings. The explanation of colour, based on 

 the change from a double linking (ketonic) to a single 

 linking (enolic), should, if sound, be capable of explaining 

 the occurrence of six bands in the spectrum of benzene, 

 four in that of naphthalene, and four in that of anthracene. 

 It is shown how this is possible from Kekul^'s formula 

 for benzene, and how this formula may be reconciled with 

 the " centric " formula. — Further studies on dihydroxy- 

 maleic acid : H. J. H. Fenton. This paper describes the 

 results of a study of the condensation of the acid with 

 ammonia, and the behaviour of the acid and its esters 

 towards various hydrazines. — The influence of light on 

 diazo-reactions, preliminary notice : K. J. P. Orton and 

 J. E. Coates, and (in part) F. Burdett. — Behaviour of 

 solutions of propyl alcohol towards semi-permeable mem- 

 branes : A. Findlay and F. C. Short. Some years ago 

 Pickering stated that when a porous pot containing a 

 57 per cent, aqueous solution of propyl alcohol was 

 immersed in either pure water or pure propyl alcohol, the 

 water or the alcohol passed inwards to the solution. The 

 authors have been unable to confirm Pickering's experi- 

 ments, and suggest that the behaviour observed by him 

 might be temporary and due to differences in the velocity 

 of the diffusion of the pure liquids and the solution. — The 

 thermal decomposition of formaldehyde and acetaldehyde : 

 W. A. Bone and H. L. Smith. Formaldehyde decomposes 

 at all temperatures between 400° and 1125° in accordance 

 with the equation CH,0 = CO-t-H„, and acetaldehyde at 

 400° in accordance with the equation CH,.CHO = CHi-|-CO. 

 — The synthesis of formaldehyde : D. L. Chapman and 

 A. Holt, jun. The authors have succeeded in synthesising 

 formaldehyde by maintaining a platinum wire at a high 

 temperature in the following mixtures : — (a) carbon 

 mono.xide and hydrogen ; {b) carbon monoxide, hydrogen, 

 and steam ; (c) carbon monoxide and steam ; (d) carbon 

 dioxide and hydrogen. — Oxymercuric perchlorates and the 

 action of alcohol on mercury perchlorates : M. Chikashige. 

 Three new oxymercuric perchlorates are described. — The 

 constitution of pilocarpine, part v., conversion of isopilo- 

 carpine into pilocarpine : H. A. D. Jowett. 



Royal Meteorological Society, May 17.— Capt D. 

 Wilson-Barker, vice-president, in the chair. — Measurement 

 of evaporation : R. Strachan. The author pointed out 

 that the rainfall, evaporation, and percolation are related 

 to each other, and that rainfall is commonly considered 

 to form the sum of evaporation and percolation. If two 

 of these quantities are found by experiment or observation, 

 the other is assumed to be known. This, however, does 

 not always hold good. A month may be very dry, and 

 still evaporation will go on at the expense of previous 

 percolation — and otherwise. A month may be excessively 

 wet, then there may be another item to take into account, 

 viz. overflow. As, unfortunately, it is not possible to 

 make evaporation and percolation the subject of experi- 



