136 ANNUAL OF SCIENTIFIC DISCOVERY. 



tion, and in a state of minuteness sufficient to keep it in suspen- 

 sion ; liut, at llic nioiut'ut of contact vvitli the peroxide of hydrogen, 

 it blackens and falls. When the peroxide is pouix'd into a solu- 

 tion of hy})i)sulphite of soda, the chanj^e is not observed, as there 

 is n<i C()lori'<l oxide to be formed; i)ut whrn a salt of barium is 

 afterward added, it is found tiiat sulphuric acid has taken the 

 place of hyposulphurous. The stren<;:th of the solution does not 

 re(juire to l)e nrn-at : that which is sold eont:iins about nint; v(j1- 

 unu's of availal)le oxyi^cn ; if dihiti'd a thousand times, a solution 

 is obtained capable of oxidizinj^ hy)>osulphites. It appears that 

 all the hyposulphurous acid is instantly converted. Peroxide of 

 hydroiren is in reality an oxide of water: when the oxyjjtui leaves 

 it to do its work, nothiiin^ but water is Itd't; nothiu<^ bciuj:!^ added 

 to be washi.'d out. The peroxide, as sold, contains a little acid 

 (sulphuric) ; when made alkaline, it does not keep so well. If a 

 drop is put upon a photojxraph, it very slowly bleaches; its use in 

 this \uidiiuted state is not recommended. A^^aiu, if the peroxide, 

 as sold, is neutralized, the bleaching does not take place, at least 

 in an hour, — an ample time. For neutralization, soda may be 

 used. — (Juarteiiy Journal of Science, July, 180G. 



UNALTERABLE PHOTOGRAPHS. 



The only mode hitherto known of producing unalterable photo- 

 graphs has bei'n by vitrification. ]M. renal)ert, however, recently 

 exhibited to the Academy of Sciences some which, though n(jt 

 vitrified, are so indestructible that it is impossible to remove them 

 from the glass, so as to render it capable of being used a second 

 time. The ojialine glass employed in the pi-ocess, having been 

 well cleaned, is to be coated with ordinary collodion that is at 

 least a year old ; it is then to be plunged for a few minutes in a 

 sensitizing bath, which contains seven grammes of nitrate of sil- 

 ver to one hundred grammes of distilbnl water, and sixteen 

 grammes of pure nitric acid to one thousand grammes of the sil- 

 ver solution, and afterward to be exposed for about fifty seconds 

 in the camera. The developing fluid consists of a solution of jiro- 

 tosulphate of iron, containing two-thirds more Avater than that 

 ordinarily used, and one-lifth i^yroligneous acid. The positive 

 picture thus obtained is fixed by a weak solution of hyposulphite 

 of soda, and is intensified by a very weak bath of sulpliuret of 

 ammonium. — Intellectual Observer, February, 18GG. 



A NEW PHOTOGRAPHIC WASHING APPARATUS. 



The majority of eases of photographic fading may be traced to 

 the hyposul^jhite of soda, which, by so intimately associating itself 

 with the fibres of the paper, is difficult of removal, and Avhich, if 

 not perfectly removed, induces an action by virtue of which the 

 print eventually becomes destroyed. To remove the hyposulphite 

 of soda in the most perfect manner, and in the shortest time pos- 

 sible, is to insure to photographs a longer tenure of existence than 

 they would otherwise have held; and any means by which these 

 requii'cments can be met are entitled to the greatest consideration. 



