H. C. Bolton—Action of Light on Uranium. 209 
the use of collodion and of a method of combining a salt of ura- 
nium with one of silver. 
Having thus sketched the history of the action of light on 
uranium, I will return to Burnett’s and Wothly’s photo- 
graphic processes. According to Burnett, ordinary paper is 
sensitized by floating on a bath of nitrate of uranium and hung 
up to dry. By exposing this paper behind a negative from one 
to thirty minutes (according as direct rays or diffused light are 
employed) a weak image is obtained which is then developed 
by a bath of nitrate of silver or of chlorid of gold. Simple 
washing being insufficient to remove the excess of silver salt, a 
bath of hyposulphite of soda may be used with advantage. 
By developing with ferricyanid of potassium, red pictures 
are obtained, and by floating these red ones on a bath of ses- 
quichlorid of iron, green pictures result.* Burnett, who studied 
this whole subject with care, did not confine himself to the use 
of nitrate of uranium, but experimented with the oxalate, tar- 
trate, formiate, citrate, acetate, succinate; benzoate, chlorate, 
bromate, oxychlorid, oxybromid, and oxyfluorid. He tried 
both acid and ammoniacal solutions. Not having been able to 
obtain Burnett’s original communications to the ‘ Liverpool 
Journal of Photography,” I cannot give details of results ob- 
tained with the various salts, but the nitrate being a commercial 
article, is the only one which ever came into use. Burnett’s ef- 
scar to obtain pictures on glass plates in a camera were unsuc- 
cessful. 
Wothly prepares a double salt by crystallizing together ni- 
trate of uranium and silver, and sensitizes a resinized collodion 
with this substance. Paper prepared in a special manner with 
arrowroot starch and albumen is then coated with the sensitized 
collodion, After exposing the print, which requires no develop- 
ment, it is toned with chlorid of gold, washed with dilute acid 
and fixed with sulphocyanid of potassium or hyposulphite ‘of 
soda. The pictures obtained by this process are said to be very 
beautiful and of a characteristic tone. oP 
In 1866 when studying the compounds. of uranium in the 
laboratory of the University of Géttingen, . obtained a salt 
; K : 
direct sunlight, decomposition ensues, a green precipitate falls, 
* The writer invariably obtained blue pictures; compare photograph No. 15. 
+ Berl, Akad., Ber. 1866, 299. 
