The quantum yield of silver production in the photolysis of silver chloride emulsion has been measured as a step to make clear the mechanism of the print out effect in this system. Emulsions of controlled excess chloride or silver ion concentrations were used and a light of relatively low intensity was employed. The yield is 0.80-0.88 at the initial stage of exposure for the 365 mμ light of intensity about 6×10¹⁵ photons/cm²·hr and depends little on the species and the concentration of excess ion, indicating sufficient provision of charge-compensating silver ions and almost complete acceptance of chlorine. With continued exposure the yield becomes smaller and dependent on the excess ion, the silver-excess emulsion having larger yield.

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The surfaces of microcrystals in photographic emulsion could be examined through X-ray diffraction method instead of an observation with microscope. The diffraction profile from the specimen having oriented microcrystals showed the proper profile to this photographic emulsion, which was available for examination of their surfaces. Such a specimen was prepared by coating of microcrystals on slide glass in single layer without coagulation and accumulation each other. Accuracy in measurement depended upon techniques for the preparation of the specimen.

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It was found that there are two types of the high speed photographic emulsion grains; one of them (I) may be desensitized by soaking in Na₂SO₃ solution before development and another (II) was not affected.
By using the fact that the solubility of AgBr in 10% Na₂SO₃ solution decreases to about 1/100 by addition of KBr (12 g/1), it was shown that the phenomenon in the former paragraph can not be attributed to the activation or inactivation of sensitive development centres but to the dissolving action of SO₃⁼ on the silver halide grains.
Assuming that the silver halid grains are homogeneous in composition, it was estimated that the depth of the dissolved surface region of the grains belonging to larger group which occupied the one half of the total projecting area but was composed of only 15% in numbers, reached
(I) to 382Å and 1290Å from the surface, respectively at 10 and 30 min. treatment (G-film, the mean grain radius in larger group γ=0.765μ) and (II) to 176Å and 590Å, respectively at 10 and 30 min. treatment (A-film, γ=0.798μ). Group (I) showed a remarkable decrease in sensitivity with the dissolved depth up to about 100Å.
Electronmicroscopic observation showed that (II) was dissolved much more irregularly than (I). The similar effect was observed by soaking the emulsion in KCN solution. The ratio of desensitization by prebath in KCN solution was (II) >(I), and. when X^- was added to KCN solution, then I^- had the greater effect in changing the ratio than Br^-.
As the result, the author would like to say that in case of (II) the silver halidegrain is inhomomogeneous in composition, such that the AgI content on some parts of the surface is higher than in (I) and that the development centres are formed on such parts. By presoaking in Na₂SO₃ solution, parts of the surface (II) having development centres are not dissolved, and so they keep the sensitivity.
Such a stable development centre could be formed by adding a cationic surface active agent, such as cethyloxymethyl-α-picolinium chloride, during chemical digestion, or better in the beginning of it, in the emulsion containing silver halide grains inhomogeneous in their composition.
As the mechanism of this effect the author supposes that: AgI which is more negative than AgBr reacts less remarkably with anions such as S₂O₃⁼ or SO₃⁼ than the latter during the chemical digestion. So in case of (I), development centres may be found in the surface parts which are dissolved by SO₃⁼, while in (II), when the emulsion is treated by a cationic surface active agent, the latter reduces the negative charge on the stable parts of the higher AgI concentration and let react them with S₂O₃⁼ or SO₃⁼. And also, the adsorption of such a substance on centres may make easier the trapping of electrons released by light.

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Recently metal-ion-chelate developer system has been researched and described by some investigators. The transition element ions, such as titanium, or iron combined with a modern chelating agent are employed as developing agents which can be regenerated in an electrical or chemical method.
The present authors surveyed the changes of the developing action and redox potential when the trivalent titanium ion is chelated with ethylenediamine tetraacetic acid. The electrode potential of the oxidation-reduction system of the sequestrated titanium ion solution was nobler than that of the free titanium ion solution, although the former was more active than the latter as a developer with the same molar concentration.

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