Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/873

PHOTOGRAPHY 837 Green AgBr in collodion, D. developed ferrous oxalate (I.e.) (s.e.) AgCl+AgNO 3 on paper P. AgCl + AgNO 3 on paper, P. slight preliminary exposure AgCl on paper washed from P. excess of AgN0 3 AgCl on paper washed, P. treated with NaCl, washed again ; also collodio- chloride of silver, and yel low AgCl in gelatin Grey AgCl in gelatin P. AgCl in collodion, excess of D. AgNO 3 or NaCl present, (I.e.) ferrous citrate or acid development Yellow AgCl in gelatin, acid D. or ferrous citro- oxalate (I.e.) development Grey AgCl in gelatin, acid D. or ferrous citro -oxalate (I.e.) development A.^ Cl in collodion, short pre- D. liminary exposure, acid or ferrous citro - oxalate development Agl + AgBr + AgNO 3 on P. paper, moist Agl + AgBr, washed from P. AgN0 3 ,, ,, developed D. ferrous citro-oxalate Agl + AgBr + AgNO 3 , wet D. plate, acid or alkaline developer Agl -f AgBr in gelatin, devel- D. oped ferrous oxalate AgBr+Agl in collodion, D. acid or alkaline developer (I.e. . . . (8.6. 3AgI + AgBr on paper P. 3 Agl+ AgBr on paper, devel- D. oped gallic acid developed ferrous D. citrate 3AgI+AgBr+AgNO 3 collo- D. dion, wet plate, acid or (I.e.] alkaline developer 3AgI + AgBr in gelatin, al- D. kaline or ferrous oxalate (1. <fc developer s.e. shown/ AgI + 3AgBr on paper or in D. collodion, ferrous citro- (I.e. oxalate developer ,, ,, (s.e. AgI+3AgBr in gelatin, fer- D. rous oxalate developer (I.e. 3AgI + AgCl + AgNO 3 on P. paper, or paper washed, both dry Agl + AgCl + AgXO 3 wet, or P. 3AgH-AgCl+KNO 2 wet 3AgI + AgCl + AgNO 3 , or D. 3AgI + AgCl + KN0 2 on paper, developed with gal lic arid or ferrous citro- oxalate are the bichromates of the alkalis. The result Spec of spectrum action in connexion with them is trum confined to its own most refrangible end, com- mencing in the ultra-violet and reaching as far 8a its. as in the solar spectrum. The accompanying diagram (fig. 2) shows the relative action of the F E D CB A No.l No. 2. V I B G Y O R Fio. 2. The top letters have reference to the Fraunhofer lines ; the bottom letters are the initials of the colours. The relative sensitiveness is shown by the height of the curve above the base-line. various parts of the spectrum on potassium bichromate. If other bichromates are employed, the action will be found to be tolerably well represented by the figures. No. 1 is the effect of a long exposure, No. 2 of a shorter one. It should be noticed that the solution of bichro mate of potash absorbs those rays alone which are effective in altering the bichromate. A reference to pp. 831, 833 will show that the change is only possible in the presence of organic matter of some kind, such as gelatin or albumen. Action of the Spectrum on Asphaltum. This Spec- seems to be continued into and below the red ; ty um ac - the blue rays, however, are the most effective, The action of light on this body is to render it less soluble in its usual solvents. Compare this statement with that on p. 822. Action of the Spectrum on Salts of Iron. Spec- Many ferric salts have been used from time to truin- time in the production of prints, the most g^ common at the present time being the ferric jr 0n> oxalate, by which the beautiful platinotype prints are produced. We give this as a repre sentation (fig. 3) of the spectra obtained on ferric H /> G No. 3 No. 4 . -^- VI B G Y O R FIG. 3. Same description as for fig. 2. salts in general. Here, again, we have an ex ample of the rigorous law that exists as to the correlation between absorption and chemical action. One of the most remarkable compounds of iron is that experimented upon by Sir J. Herschel and later by Lord Rayleigh, viz., ferro- cyanide of potassium and ferric chloride. If these two be brushed over paper and the paper be then exposed to a bright solar spectrum, action is exhibited into the infra-red region. This is one of the few instances in which these light waves of low refrangibility are capable of pro ducing any effect. The colour of this solution is a muddy green, and analysis shows that it cuts off these rays as well as generally absorbs those of higher refrangibility. Action of Light on Uranium, The salts of Light uranium are affected by light in the presence of actio . n on , T . i uranium, organic matter, and they too are only acted upon by those rays which they absorb. Thus nitrate