13 2-1/3
14 3
15 4
16 5
17 7
18 9
19 12
20 16
21 21
22 27
23 36
24 48
25 63

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: