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Screen-Plate Practice
519
sure errors with pyro-ammonia than with metol-hydroquinon, and also suggested a tentative method of adding the ammonia gradually.
The ready oxidation of pyrogallol is to some workers a great objection, and MM. Lumiere;7 suggested the following as obviating this difficulty :
Metoquinon (Quinomet) 4 g.
Sodium sulfite, anhydrous 18 g.
Ammonia, sp. gr. 0.920 6 ccs.
Potassium bromide 1 g.
Water to 1000 ccs.
Time of development 2l/2 minutes at 18° C. for correct exposure. A more elastic developer, which should permit of correction of errors in exposure was later38 given :
Metoquinon 15 g.
Sodium sulfite, anhydrous 100 g.
Ammonia 32 ccs.
Potassium bromide 6 g.
Water to 1000 ccs.
For use 5 parts of this stock solution should be mixed with 100 parts of water. For correction of exposure the following method was advised. Place in two separate graduates 15 and 45 ccs. respectively of the above stock solutions. Immerse the plate in the dilute solution, and count the number of seconds till the first appearance of the image, exclusive of the sky in landscape work. The total time of development was then determined according to the following table : Immediately the outlines arc discernible, pour into the dish either 15 or 45 ccs., which ever may be necessary according to the table, continuing to count the seconds :
Appearance of outlines
Quantity of developer to add on first
Total duration of development from first
appearance of outlines
immersion
ot plate
Seconds
Ccs.
Minutes
Seconds
12 to 14
15 ccs.
1
15
15 to 17
15 ccs.
1
45
18 to 21
15 ccs.
2
15
22 to 27
15 ccs.
3
—
28 to 33
15 ccs.
3
30
34 to 39
15 ccs.
4
30
Extreme 40 to 47
45 ccs.
3
—
Underexposure above 47
45 ccs.
4
—
The Lumiere N. A. Co.88 issued subsequent to April 1, 1909 the following instructions, which involve the use of two baths only:
Quinomet 4 g.
Sodium sulfite, anhydrous 18 g.
Ammonia, sp. gr. 0.920 6 ccs.
Potassium bromide 1 g.
Water to 1000 ccs.