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466
History of Three-Color Photography
118 from photomicrographs, taken by the author31 and the preponderance of the green and also the clumping is evident.
Von Hubl32 found that the substratum that holds the grains was completely soluble in benzol, which goes to show that it is rubber. Treatment of the plate with alcohol dissolves the film of varnish over the grains, and water dissolves the dye from the red and green grains, but leaves the blue untouched. Jung33 found that alcohol, ether, chloroform and oil of cloves very quickly decolorized the grains, but water only slowly and he considered the dyes to be safranin, iodine green and methylen blue. He also considered that the starch was maize and not potato. F. M. Duncan34 said it was wheat starch because it did not show the familiar hilum and black cross by polarized light. J. H. Pledge35 and W. Scheffer36 proved
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Fig. 117. Violet
Fig. 118. Green
that this observation was erroneous. The latter also stated that by prolonged soaking in xylol, the rubber substratum was so softened that the film of colored grains and the gelatin could be stripped from the glass, although it took a long time, as the xylol had to find its way in from the edges.37
Some discussion arose at first as to the actual medium used for the emulsion, probably from its character differing so much from that of the ordinary plate. C. Wolf-Czapek38 and R. Neuhauss39 considered it to be collodion. A. Haddon40 thought it was some starch or feculose preparation. J. Gaedicke41 stated that a gelatin emulsion was used and its thickness was 0.005 mm. Lumiere and Seyewetz42 definitely stated that nothing but a gelatino-bromide emulsion had ever been used, in accordance with the patent specification.