: W. Crookes on the Wax-paper Photographic Process. 169 
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iodid of silver per se was the best sensitive surface for receiving 
4m image in the Camera; but on making use of that body in 
__ these operations, (by employing pure iodid of potassium in the 
_ bath,) I was surprised to meet with results, for which I was at 
first unable to account. A little consideration, however, showed 
‘me the direction in which I was to look for a remedy. The ex- 
periments which had led me to prefer iodid of silver as a sensi- 
tive surface, had all been performed with sunlight, either direct, 
or more frequently in the form of diffused daylight. In this 
case, however, coal gas was the source of light; and if, as was 
_ very probable, there were any great difference in the quality of 
_ the light from these two sources, the superiority of iodid over 
the bromid or chlorid of silver would still be a matter for ex- 
3 nd + , 
 - periment. Z 
____ 384A comparison of the spectra of the two kinds of light 
a : en . . 
_ Sitions were fully borne out by experiment: on introducing a 
little bromid of potassium into the i bath 
potassium + odizing bath, the change was 
very apparent. It requires a certain proportion to be observed 
between the two to obtain the best results. If the iodid of 
potassium be in excess, the resulting silver salt will be wanti 
in sensitiveness, requiring a comparatively long development to 
render an image visible; while, if the bromid be in excess, there 
will be a great want of vigor in the impression, the picture being 
red and transparent. When the proportion between the two is 
properly adjusted, the paper will be extremely sensitive, the 
pecatite. presenting a vigorous black SPpeArsnag without the 
least approach to cutee addition of a chlorid was found to 
SECOND SERIES, VOL. XXII. NO. 65,—SEPT., 1856, 
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