1881.] Spectrum on the Haloid Salts of Silver, fyc. 185 



chloride and washed and dried, or if exposed in the presence of 

 dried silver nitrate or dried potassium nitrite, we have the curve 

 shown in fig. 64. If, on the other hand, we have the same paper 

 exposed moist, with silver nitrate or potassium nitrite we have the 

 curve shown in fig. 65. The reasoning applied to the mixture of 

 iodide and bromide applies with equal force here, the results being 

 modified for the shift of maximum of the chloride which lies about 

 \ Hh. In fig. 64 the most refrangible part of the spectrum as far as 

 G is ruddy, between G and F a pink colour, and beyond that grey. 

 This difference in colour indicates (as it does in all other photo- 

 graphed spectra where different colours are impressed or developed) a 

 difference of compound acted upon. According to our theory the 

 molecule acted on beyond G in the violet and ultra-violet would be 

 Ag. 2 I 2 + AglCl, and between G and E Ag 2 ICl + Ag 2 Cl 3 alone. The 

 grey here is probably due to the organic silver compound formed in 

 the paper. 



Fig. 66 shows the same equivalents if contained in paper or 

 collodion, and when exposed to light in the presence of moist silver 

 nitrate or other inorganic sensitiser and developed by acid or ferrous 

 citro-oxalate developer, the slight modification due to the former 

 developer noted above still holding good. Fig. 67 shows the same 

 paper or collodion emulsion washed and developed with ferrous 

 citro-oxalate. Fig. 68 shows the same when emulsified in gelatine 

 and developed with the same ferrous developer. There is a difference 

 in the curves obtained with collodion and gelatine, but not more than 

 is explainable by the fact that the former is essentially porous and the 

 latter almost continuous. 



One Equivalent of Iodide to Three of Chloride. — When three equiva- 

 lents of silver chloride are taken with one of iodide, we have, on 

 printing a washed paper, the curve shown in fig. 70 ; exposing the 

 same paper moist in the presence of silver nitrate we have fig. 71 ; 

 the reasoning given when the mixture of bromide and iodide was 

 under consideration holds good. Figs. 72 and 73 show the same 

 equivalents of sensitive salts held in paper, the former showing the 

 action of development on washed salts and the latter on the same 

 exposed in the presence of moist silver nitrate. 



Fig. 69 shows the effect of the spectrum on equal proportions of 

 the iodide and chloride when emulsified in gelatine. 



Paper and also collodion films containing silver chloride were 

 blackened in the light and treated with a solution of iodine till the 

 darkening was obliterated, washed, and then exposed, with or without 

 sensitisers ; we had nearly the same results on printing and on 

 development as shown in fig. 74, hence, it was thought useless to 

 repeat the curve there shown. (The same applies to darkened 

 bromide treated with iodine, exposed to the spectrum and developed.) 



O 2 



