EDWARD ELSWORTH. 131 
or less quantity, and collodion, when dry, hardened into 
an impenetrable film, which the developing agent could 
not enter. 
About 1870, one Thomas Sutton, in an essay which 
years after was published in the British journal of pho- 
tography, gave the first clear, definite suggestion for an 
improvement of Gaudin’s emulsion, in which he proposed 
that collodion be discarded entirely, and gelatine only be 
used instead. His theory was that, by using a gelatine 
emulsion with bromide of silver, a structureless and ho- 
mogeneous film, exquisitely sensitive withal, would be 
formed. 
He concluded a minute exposition of his theory with 
these words: ‘‘ It may turn out that I have done well in 
digging up this old process of M. Alexis Gaudin, whose 
name be exalted as the anthor of collodion emulsions 
and photogenes.”’ 
Sutton died soon after, without having seen his theory 
put to test; but the seed he had sown fell into good 
ground. Karly in 1871, Dr. R. L. Maddox made a gela- 
tine bromide of silver emulsion, with which glass plates 
and paper were coated, but they were only fairly sensi- 
tive, and failed for reasons which are now well recog- 
nized. Dr. Maddox was obliged to give up his experi- 
ments on account of failing health, but others took up 
the subject. In 1873, a Mr. Kennett, an amateur, pat- 
ented a process for making a gelatine bromide of silver 
coating, which marked a great advance over any of the 
methods theretofore suggested by Gaudin, Sutton or 
Maddox. His method was to wash out of the emulsion 
all of the free salts left therein after the mixture. The 
omission to perceive the necessity of this was the cause 
of Maddox’s failure. Kennett’s plates were really the 
first satisfactory plates upon the market. In addition to 
their other good qualities, they were very much more 
sensitive than any which had previously been used. 
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