384 
POPULAR SCIENCE REVIEW. 
remove all trace of the hyposulphites from the paper by washing, it is certain 
that they do fade, and few dispute the final cause of such a fading. Therefore, 
a discovery which destroys these mischievous agents altogether cannot but be 
regarded as most important, and such a discovery it is our pleasing duty to 
announce as having been recently published by Dr. Angus Smith, F.E.S., in 
the pages of The British Journal of Photography , from which we quote : — 
“ Considering that the cause of the destruction of photographs, apparently 
by the action of time only, was in reality caused by the amount of hypo- 
sulphite remaining in the paper, D. Eeissig, of Darmstadt, contrived a mode 
of washing it out by centrifugal force. For indicating the presence of sulphur 
acids, he uses a small galvanic arrangement with one cell, and decomposing 
the acid, had the sulphur thrown on a piece of polished silver, which 
became readily blackened in the solution. Dr. Theodore Eeissig, my 
assistant, examined several faded photographs for me by his brother’s 
method, which, however, appeared unnecessarily delicate, as it was found 
that the amount of sulphur was very large, and roughly, we thought, 
in proportion to the amount of decay. I did not determine how much was 
hyposulphite and how much sulphate. As I had been interesting myself in 
bringing into use some of the remarkable properties of peroxide of hydrogen 
in oxidizing metals and organic bodies in fluids, it seemed to me that we 
might readily use it for oxidizing the hyposulphites. I am supposing that the 
sulphate alone will not be injurious.” Dr. Smith then shows how this power- 
ful oxidizing agent may be used to convert the mischievous hyposulphites 
into the innocuous sulphate, and Mr. Dawson, in the same number of the 
journal, gives the following experimental illustration : — “Dissolve in a wine- 
glass any quantity of sulphate of soda, and add to the solution a few drops 
of tincture of iodine. The solution will remain permanently discoloured, 
showing that sulphate of soda does not dissolve iodine. In another wine- 
glass, half filled with plain water, drop sufficient tincture of iodine to strike 
a permanent dark sherry colour throughout the liquid ; then add, drop by 
drop, a weak solution of hyposulphite of soda till the colour is discharged, 
taking care to add as little excess of hyposulphite as possible. So far this 
experiment shows that iodine is soluble in hyposulphite of soda. Now fill up 
the glass with an aqueous solution of peroxide of hydrogen, and observe the 
effects. After a few minutes the iodine is no longer held in solution, and the 
liquid will resume the dark sherry colour it had before adding the hyposul- 
phite of soda.” Eveiy chemist will readily explain this. To apply this new 
chemical agent to this new use, take the print, after fixing and washing, and 
soak it for a short time in a solution of the peroxide of hydrogen of the 
strength of say one ounce of a ten-volume solution in forty ounces of water. 
Opaltypes . — The photographic serials often amuse us by showing upon 
what slight and insufficient grounds a person can sometimes dub himself 
“ inventor,” and what a trifling modification of some old process frequently 
constitutes what is called “ a new process.” Such pages chronicle the rise and 
fall of an extraordinary number of these photographic ephemera. Amongst 
the most attractive perhaps have been the modifications of what is most 
widely known as the opaltype, to which we called attention some time since ; 
but of late complaints have been rife as to the unreliable nature of all these 
“ processes,” and most of them have therefore been quietly deposited with 
