186 Effect of Spectrum on Haloid Salts of Silver. [Dec. 15,. 



This appears to be a confirmation of the view already propounded 

 regarding the formation of a new molecule, in the case of the chloride 

 and iodide the new molecule taking the form of Ag 2 ClI, as already 

 indicated. 



From these results we may observe that to obtain a compound 

 sensitive to the green a mixture of iodide and bromide, or iodide and 

 chloride, should be employed, the former in preference to the latter, 

 since it is more sensitive. The same sensitiveness to daylight with 

 the former in gelatine plates can be obtained as when using pure 

 bromide alone, the sensitiveness being preserved by a shift of the- 

 maximum to the green. 



Mixtures of Silver Chloride and Bromide. 



There is nothing special calling for remark in a mixture of these 

 two sensitive salts. The printed spectrum and the developed spec- 

 trum seem to be a combination of the spectra impressed on each 

 individually, a slight prolongation towards the least refrangible end 

 taking place. 



Mixture of Silver Iodide, Bromide, and Chloride. 



When these three salts are combined together we have spectra 

 which are very similar to the spectra produced on iodide and chloride,, 

 or iodide and bromide, with a prolongation towards the red. 



Concluding Remarks. 



In a paper read, in 1880, before the Photographic Society of 

 Great Britain, I recommended the addition of a small quantity of 

 iodide to the bromide used in the preparation of gelatine emulsion. 

 On carefully examining spectra photographed on such plates (having 

 part of iodide to ±± of bromide) I find traces of the loss of 

 sensitiveness about Gr. I stated also that addition of iodide diminished 

 the sensitiveness of the bromide to the red rays ; an examination of 

 curves given for the mixtures of bromide and iodide of silver bears 

 out my statement. 



It will be noticed that I have not touched upon organic sensitisers 

 of the haloids, prepared with an excess of silver and then washed, and 

 such sensitiser applied. I have only treated of the haloids themselves, 

 endeavouring to eliminate every extraneous effect which would modify 

 the action of the spectrum. I purpose in a subsequent communication 

 to enter into this part of the subject. 



