212 H.C. Bolton—Action of Light on Uranium. 
The actinic reactions of uranium salts much resemble those 
of iron ; like the latter the sensitive uranium compounds all 
contain oxygen and the physical and chemical changes are due 
to complete or partial deoxydation. We also notice the neces- 
sary codperation of organic matter, the part which the latter 
plays being clearly that of a reducing agent. Under influence 
of the actinic rays, the uranium salts part with some of their 
oxygen, which goes over to the oxydizable organic material. 
An aqueous solution of nitrate of uranium exposed to light 
in a glass vessel remains unchanged ; but as soon as organic 
matter whether in the form of alcohol, ether, glycerine, cellu- 
lose or an organic acid, is brought in contact with the uranic 
solution a reduction is effected and the organic matter is oxyd- 
ized at the expense of the uranium. Accordingly, salts of 
uranium with organic acids are for the most part sensitive as 
such. In the printing processes, cellulose effects the reduction, 
which is, however, assisted by the addition of alcohol (recom- 
mended by Hagen) or glycerine, 
_ Attempts to obtain reactions with other agents than the ac- 
tinic rays of the sun, gave negative results. A series of 23 
uranium salts exposed to the light of magnesium wire, exhl 
ited no fluorescence, nor was a solution of the oxyfluorid with 
formic acid reduced by exposure to the magnesium light. AD 
experiment made with the intention of effecting reduction at 
a high temperature under pressure, was also unsuccessful. 
solution of the oxyfluorid acidified with formic acid was heated 
in a sealed tube at 100° C., and afterward at 120° C. for many 
hours, but without producing the least change. 
Details o manipulation, strength of solutions, &c., such as 
may be found in any practical work on photography, have been 
purposely omitted, it being my object to consider the subject 
strictly from a chemical point of view. 
Description of Photographs. 
No. 1. (Jan. 25, 1868.) —Common filtering paper sensitized 
with a mixture of oxyfluorid of uranium and potassium and 
formic acid. Exposed ten days. Fixed by washing. Barely 
perceptible outline, 
ORES 
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