ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 105 



issue. Whether or not it will be found to fulfil the conditions necessary 

 to establish itself as a standard or commercial process, only time can 

 prove. It is a triple film method, but differs from those previously 

 proposed, in that each colour is printed out by light. 



Many of the organic dye-stuffs yield on reduction colourless or 

 leuco-derivatives, which can be oxidised to reproduce the original colour 

 ■with more or less facility, and exposure to light generally facilitates this 

 oxidation. By choosing a dye of a suitable colour, and one that yields 

 a leuco-derivative of sufficient stability to withstand the necessary 

 operations and yet is sensitive enough for practical printing purposes, 

 it is obvious that the colour may be obtained directly by exposure to 

 light under the negative, and the necessity for a relief produced by the 

 chromated gelatin process, or any similar indirect method of getting 

 -the required distribution of the colour, is obviated. 



These leuco-derivatives were found to be useless by themselves or in 

 an inert film, as they then gave only poor and flat images, but the 

 presence of a nitric acid ester was discovered to overcome this difficulty. 

 Pyroxylin being an ester of nitric acid a collodion film is employed, 

 and mannite nitrate is very suitable for further augmenting the sensi- 

 tiveness. The removal of the excess of the leuco-derivative after 

 exposure was at first a difficulty, as ordinary solvents and acids were 

 found useless for the purpose. But monochloracetic acid is effective, 

 and it is used as a 10 p.c. solution. 



The process consists in coating a suitably surfaced paper with a 

 1| p.c. collodion, to which the leuco-derivative and other desirable 

 materials have been added, exposing under the appropriate negative 

 until the colour is sufficiently intense, fixing in the chloracetic acid 

 solution, washing, and dipping into a gelatin solution that contains 

 •chrome alum, and drying. The print is again dipped into the gelatin 

 solution and dried to effectively protect the collodion film during the 

 application of the collodion that is to furnish the second colour. This 

 routine is repeated for the second colour, and again for the third, and 

 the print is finally varnished. 



The method of judging when each colour is correctly printed is not 

 very clear, as it seems impossible to adjust the depth of tint of the 

 films that are sealed up by the subsequent coatings. The process is 

 apparently rather tedious, as there are three collodion films, six gelatin 

 coatings, and a final coating of varnish to dry. The obvious objection 

 to the number of films because of their combined thickness is probably 

 invalid, as the collodion and the gelatin solution used are weak, and the 

 films they give correspondingly thin. A real difficulty I should have 

 expected to be due to the action of the chloracetic acid on the gelatin 

 films under the collodion film that is being subjected to the fixing 

 operation, but doubtless this possibility has received attention. 



Lumiere's Starch Method of Three-Coloiir Photography. — This process, 

 which was described about six months ago, contrasts very emphatically 

 with Konig's method in the simplicity of the necessary manipulation. 

 No colour-screens or filters are needed, there are no films to stain, no 

 -colours to produce of the correct intensity to match one another, no 

 separate negatives with subsequent printings, but merely one exposure, 



