176 COLOR PHOTOGRAPHY. 



III. — Chemical Relations op Chloride of Silver during 

 Exposure and Electrolysis. 



It lias been lately shown conclusively by G-untz 1 that in the exposure 

 of silver chloride to light silver protochloride is formed. Pure silver 

 chloride not exposed to light appears, according to Becquerel, 2 to be 

 appreciably sensitive, when exposed to the spectrum, only to violet and 

 ultra violet light, and takes on during exposure a violet color. I have 

 repeated this experiment with the same result. The resulting powder, 

 composed of silver chloride and protochloride, is, however, sensitive 

 to all colors of the spectrum and copies them to a certain degree. 



It would be desirable to investigate whether pure silver protochlo- 

 ride is changed in the spectrum. Dr. Hermens, assistant in the tech- 

 nical chemical laboratory of this institution, has with great friendliness 

 endeavored to prepare some of this salt for me, following the directions 

 of Guntz. 3 It appears, however, to be very difficult to obtain it free 

 from silver chloride. Guntz, indeed, secured no pure silver protochlo- 

 ride. 



The chemically prepared silver protochloride behaves in the spec- 

 trum in the same way as exposed silver chloride. This experiment, 

 therefore, forms a confirmation of the proof of Guntz of the formation 

 of silver protochloride by the action of light on silver chloride. The 

 mixture of silver chloride and protochloride had the violet appearance 

 of exposed silver chloride. 



The electrolytically prepared chloride of silver contains also some 

 silver protochloride. For it is sensitive to all rays of the spectrum. 

 It can not, however, be exclusively silver protochloride; for in one 

 experiment I obtained a plate which was "sensitive only to violet and 

 ultraviolet rays, and which therefore contained only silver chloride. 

 In its preparation I had not observed the conditions of the experiment. 

 It was probably produced by too weak a current, for I later prepared a 

 plate with a current of 0.2 amperes which was very sensitive in the 

 ultraviolet but only slightly so in the visible spectrum. It must there- 

 fore be assumed that Becquerel plates thus prepared consist principally 

 of silver chloride with some protochloride, the quantity of which is 

 increased with stronger currents. In confirmation of this it may be 

 remarked that when the layer is lifted from the silver surface it appears 

 of a bright violet color, by transmitted light. 



IV. — The Accuracy of the Color Reproduction in the 



Older Processes. 4 



Becquerel's plates give the colors by far the best. They appear 

 bright, similarly to those produced by Lippraann's method, and in the 

 right places. 



1 Guntz. Comptes rendus, 113: page 72. 1891. 



2 P>et;f[uerel, Annates do chiinio et do physique (3), 22: page 452. 1848. See also 

 Zenker, Photochromie, page 18. 



:; Gmitz. Comptos rendus, 112: page 861, 1891, 

 4 iSeo also Zenker, loc, cit. 



