EDWARD ELSWORTH. 1838 
a second ; while others represented exposures between 
these two extremes. 
This exhibition was such a surprising revelation that 
Mr. Bennett was appealed to to give the secret of his 
process to the world. This he generously did, and the 
secret proved that he had profited by Stas’ researches, 
and that the essential point in the process was the appli- 
cation of heat to the emulsion. The Liverpool Dry Plate 
Company soon after put Bennett’s plates upon the market. 
Of course, Bennett’s success stimulated a vast amount 
of experimental research after some improvement of the 
process, the most important of which proved to be the 
boiling of the emulsion itself, by which the sensitiveness 
was more readily controlled, and the time consumed in 
the preparation greatly decreased. 
Substantially, the process of making dry plates is to- 
day the process which Bennett gave to the world just 
eleven years ago. While a great many manufacturers 
of commercial plates, both in Kurope and America, are 
each claiming some point of superiority, either in sensi 
tiveness or ease of manipulation, the process of manu- 
facture is substantially as follows : 
Certain proportions of pure gelatine, some bromide, 
either of potassa or ammonium, and distilled water, are 
combined until the gelatine is well swollen, and then the 
vessel containing the mixture is placed in a bath of warm 
water until the ingredients are dissolved ; or, if preferred, 
the bromide is first dissolved, and then the gelatine 
added. Nitrate of silver, previously dissolved in water, 
is then added, together with a small quantity of nitric or 
acetic acid ; agitating the whole mass very vigorously 
during these operations. The mass is now placed in 
boiling water and kept there, with frequent stirring, from 
one-half of an hour to two hours, according to the sensi- 
tiveness required. The mixture is next transferred to a 
bath of ice water, in which it is allowed to remain until 
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