August, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



211 



Photography. 



Pure arvd Applied. 



By Chapman Jones, F.I.C, F.C.S., &c. 



The Action of Hydrogen Peroxide on Photographic 

 Plates.— Dr. Chiri Otsuki has made a communication 

 (Jour. Soc. Chem. Ind., 1905, p. 575) on this subject, 

 in which he confirms many of the results obtained by 

 Dr. Russell some years ago. What seems to me the 

 most important detail in this communication, though 

 the author appears to regard it as of very little import- 

 ance indeed, is the statement that a plate that had been 

 acted on by hydrogen peroxide and that would have 

 given an image by development, partly lost the possi- 

 bility of development by " laying the photographic plate 

 for eleven minutes in water," and that " after leaving 

 it one hour in water after the exposure no picture of 

 the hole was obtained." It seems that Dr. Otsuki's 

 onlv conclusion from this is that the developable possi- 

 bility is due to something (hydrogen peroxide) con- 

 densed on it, and that may be washed off or out of it. 

 But developable silver bromide cannot be watered back 

 into the undevelopable variety. If the peroxide can be 

 washed away and leave the plate unaffected, then it 

 does not produce the developable condition at all, but 

 merely co-operates with the developer, in the absence 

 of light, to reduce the silver bromide to the metallic 

 state. Or it may be that the developable condition pro- 

 duced by a form of radiant energy emanating from the 

 peroxide is destroyed by the soaking in a weak solution 

 of the peroxide, though this latter explanation appears 

 hardly tenable in face of the fact that Dr. Luppo- 

 Cramer in his experiments immersed the plates in solu- 

 tions of hydrogen peroxide. In any case this possi- 

 bility of washing away the peroxide, and with it any 

 effect that it may have produced, is of the greatest 

 importance, if it can be confirmed. Theories ought to 

 count for very little while facts are in doubt, therefore 

 I do not think it worth while to refer to those put for- 

 ward by Dr. Otsuki, especially as they appear to me 

 to be founded on many false assumptions. I still think 

 that some of the results obtained by Dr. Russell and 

 those who have followed him cannot be explained on 

 the simple vaporization theory, and I see no reason to 

 qualify the remarks I made on these experiments seven 

 years ago, and in the last January and February num- 

 bers of this journal. 



The Spectrum as a Photographic Test. — It is difficult 

 for the person who has not been scientifically trained to 

 appreciate the statement that the spectrum is, and must 

 be, the only final test object in all experiments concern- 

 ing colour sensitiveness, colour reproduction, and the 

 like. It seems to be a common idea that scientific 

 instruments can be used and the results they give 

 interpreted by anyone who can use the instruments in 

 the sense in which one uses a tourist's telescope. Of 

 course, this is a grave error, but it accounts in large 

 measure for the ideas held by many that spectrum tests 

 are deceptive, that as spectra " do not grow on trees " 

 they are not suitable objects to work with in seeking 

 for methods of photographing Nature, and that a 

 process may be right spectroscopically but not right 

 when tested with pigment colours. The expression 

 " the spectrum," that one is forced by custom to em- 

 ploy, is deceptive, for it often conveys the impression 

 that there is a spe:trum or some particular spectrum 



that is the standard spectrum, and so hides from the 

 merely practical mind the fact that spectra are as 

 numerous as lights — indeed, may be far more numer- 

 ous, and that in dealing with a spectrum one has the 

 given light simplified by being separated into its com- 

 ponent parts. But this very simplification when 

 unwisely done may be a source of confusion and error, 

 as if one in seeking for the beauties of language in a 

 piece of writing were to dwell unduely upon the etymo- 

 logy and the spelling of the words. 



A spectroscope is really a very dangerous guide in 

 the hands of those who do not thoroughly understand 

 it; it is too often like a micrometer in the hands of a 

 tailor, unnecessary, troublesome, and misleading. 

 Those who have not made a special study of its use 

 should have but little to do with it; they should rely 

 upon a judicious selection of pigments or coloured 

 glasses. With these a great deal can be done; per- 

 haps, indeed, all that is necessary for practical pur- 

 poses. But at the same time, final and inclusive work 

 can be done only spectroscopically, and only by one 

 who is really expert in the use of the instrument for the 

 particular purpose required. 



For ordinary photographic purposes in connection 

 with colour, I think that the chief difficulties peculiar 

 to this kind of work result from the unequal dispersion 

 given by prisms, the employment of a too small or too 

 large dispersion, and the giving of unwise exposures. 

 It is generally desirable to give a series of exposures in 

 geometrical ratio, and it may be necessary to reduce 

 with a coloured screen the light that is most active. 

 Of course, there are many other experimental diffi- 

 culties which are common to all spectroscopic work, 

 and others common to all photographic work. 



Oxidation of Sodium Sulphite Solutions. — The oxida- 

 tion of sodium sulphite by exposure to the air takes 

 place far less readily than is often supposed. The 

 effiorescence on the crystals has been taken by many 

 chemists as evidence of the presence of sodium 

 sulphate, whereas it is due merely to the loss of water 

 of crystallization. Solutions of the salt are also stable 

 if preserved with common care. Messrs. Lumiere and 

 Seyewetz have recently observed that they are even 

 less liable to oxidation if a small quantity of a developer 

 is added, and they give the following list, placing the 

 substances in order of their effectiveness. Hvdro- 

 quinone is the best; then follow, paraamidophenol (the 

 active agent of " rodinal "), glycin, paraphenylene- 

 diamine, catechol, metol, " metoquinone," amidol, 

 adurol, edinol, and eikonogen. The addition of alkalies 

 or their substitutes, such as acetone or formaldehyde, 

 diminishes the preservative action. Hence the idea that 

 a one-solution developer, especially if made with hydro- 

 quinone and also in the case of " rodinal," is peculiarly 

 free from liability to spoil by exposure, seems to be 

 founded on fact. 



Competition. — The Thornton-Pickard Manufacturing 

 Co., of Altrincham, are offering several series of cash 

 prizes for photographs taken under conditions that will 

 be sent on application. The entries must be received 

 before October i. 



The Potentia Organization. 



An international organization is being formed by a number of 

 influential representative men to establish amongst nations a mutual 

 relationship and co-operation for the diilusion of accurate informa- 

 tion on events effecting the peace of the world. Sir Vincent 

 Caillard, Professor G. H. Darwin, and Sir Michael Foster are the 

 English representatives. 



