210 H. 0. Bolton—Action of Light on Uranium. 
and the liquid becomes ‘colorless ; the precipitate is insoluble 
in water and dilute acids, and has the composition 4(U Fl)+ 
K Oxalic acid effects a similar reduction, but with the for- 
mation of Ebelmen’s violet hydrate as secondary product. I 
have made many attempts to obtain green prints with this 
salt. Last winter I exposed behind a negative, paper sensitized 
with oxyfluorid of uranium and potassium to which a little for- 
mic acid was added. After ten days constant exposure faint 
indications of a picture were perceptible.* This was not very 
promising, but I recently repeated the experiment, first floating 
the paper on a bath of formic acid and then on a bath of oxy- . 
fluorid of uranium and sodium, it being more soluble than the 
corresponding potassa salt. In one hour a weak print is ob- 
tained which scarcely becomes darker by longer exposure ; 
owing to the simultaneous formation of the green fluorid and 
the violet hydrate, the picture when first printed presents a sin- 
gular appearance. Simple washing with water removes the 
excess of uranium salt and fixes the green parts, but the violet 
parts turn yellow and weaken the image.t Could the forma- 
tion of the violet hydrate be prevented, one might obtain uni- 
form prints of a delicate green. By exposing paper sensitized 
as above for a shorter period, one to two minutes, and develop- 
ing with nitrate of silver or ferricyanid of potassium the usual 
black and red pictures may be obtained. These, however, are 
no novelty, but experiments with certain metallic salts to ascer- 
an their value as developers brought out some interesting Te- 
sults. 
At this time, not fully cognizant of the completeness of Bur- 
nett’s experiments, I attempted printing with other salts of 
the solutions and evaporating. The golden ee 
out effect, ferricyanid of potassium and sulphid of ammonium 
only darken*the liquid, the presence of citric acid prevent 
their action as in the case of iron, manganese and aluminiw 
On boiling with caustic potash the solution is decomposed wit 
* See Photograph No. 1. Phot hs No. 2 and No. 3. 
_ } See Photographs Nos. 20 to 24. Seas ats : 
ing 
m. 
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