350 



E. KLEIN 



Figs. 1-3. Carbon replicas of silver halide grams. /Ig. J, ammonia emulsion, silver bromide (carbon replica). Fig. 2, 

 boiling emulsion (non-ammonia), silver bromide (carbon replica). Fig. 3, silver iodide emulsion (carbon replica). 

 Fig. 4. Slightly etched silver bromide grains. 



ges and Mitchell (4) with a light microscope on large 

 silver bromide single crystals is quite definitely 

 brought about by clefts of less than 50 A in size; in 

 other words, that the inner surfaces making their 

 appearance in this respect are less widely spaced. It 

 would appear, therefore, that the sub-structure is 

 only the result of displacements and spaces in the 

 magnitude of one or a few lattice intervals.' Of 

 course it is possible for sub-structure also to be 

 present in the silver bromide crystals of normal 

 photographic emulsions. 



Usually it is assumed (3) that inner surfaces in 

 the crystal could arise from crystal growth due to 

 grain conglomeration. However, examination of va- 

 rious types of emulsion precipitations with an elec- 

 tron microscope have confirmed that conglomeration 

 is of importance only in the first stage of the preci- 

 pitation, i.e. with the extremely fine grains. The 

 growth of grain is due entirely to accumulation of 

 the newly forming silver halide on grains already 

 present and to Oswald ripening." 



Figs. 5-6 show a comparison of developed grains 

 from the same silver bromide emulsion. Fig. 5: 



normal metolquinone developer; fig. 6: p-phenylene- 

 diamine developer. The fine structure of the devel- 

 oped silver is considerably coarser in the case of 

 the /7-phenylenediamine development.'' 



Experiments on initial development show the for- 

 mation of a single silver filament from a silver bro- 

 mide crystal and also three etching pits alongside 

 each other at angles of 120 to the centre of the 

 crystal (2, 6) (fig. 7). This phenomenon has already 

 been investigated by Evans and Mitchell (2) with a 

 light microscope. 



The silver filament forming on the developing 

 nucleus probably arises from silver ions which move 

 from the etching pits over the surface or possibly 

 right through the crystal to the growing filament. 



When developing pure silver iodide crystals (Fig. 



' Mr. Mitchell confirmed this view during a discussion 

 held with him. 



- From a combined report with Dr. Saleck, Agfa AG, 

 Leverkusen. 



^ The effect upon the "graininess" of a photographic 

 emulsion (medium variation in density) will have to be 

 discussed on another occasion. 



Figs. 5-6. Differently developed silver bromide grains. 

 Fig. 5, metolquinone developer (carbon replica). Fig. 6. p- 

 phenylenediamine developer (carbon replica). 



Figs. 7-8. Initial development results. Fig. 7, fiat silver bro- 

 mide crystals. Fig. 8, silver iodide crystals. 



