Dr. Eder has recently published, in the Correspondenz, the first of a series of articles embodying the results of his more recent work on gelatino bromide; and we now reproduce the substance of the article in a somewhat abstracted form.

The "sensitiveness of a wet" plate continues to be used as a rough and ready standard of comparison; and, notwithstanding the fact that it is physically impossible to exactly compare the sensitiveness of a wet plate with that of a gelatino bromide film, it is convenient to refer to wet plates as some kind of a rough standard.

Experiments have shown that a gelatine plate which gives the number 10 on the Warnerke sensitometer, may be regarded as approximately corresponding to the average wet plate; and setting out from this point, the following table has been constructed:

Sensitometer
number.
Sensitiveness,
expressed in terms
of a "Wet Plate."
101
111-1/3
121-3/4
132-1/3
143
154
165
177
189
1912
2016
2121
2227
2336
2448
2563

The nature of the developer used has, of course, some influence on the sensitiveness of the plates; but in the above cases it is assumed that oxalate developer, without any addition, is used; or pyro., to which ammonia is added at intervals of about thirty seconds, so as to produce a slight tendency to fog; the time of development being from three to four minutes. The numbers are supposed to be read after fixation, the plate being held against the sky.

Schumann's statement that a gelatino bromide plate is less sensitive when developed at 30° C. than when developed at 5°, is contested; the more recent investigations of Dr. Eder serving to demonstrate that a developer at a moderate high temperature acts very much more rapidly than when the temperature is low; but when a sufficient time is allowed for each developer to thoroughly penetrate the film, the difference becomes less apparent. Here are examples:

A. - Oxalate Developer.
Temperature of developer4-8° C.16-17° C.26-28° C.
Time of development1 min.3° W.8° W.13° W.
"2 min.9½° W.10° W.15° W.
B. - Pyrogallic Developer.
Temperature of developer1-2° C.26-28° C.
Time of development¼ min.6° W.10° W.
"3 min.14° W.15° W.