Scientific Papers of the Bureau of Standards Volume 17, Nos. 405-438 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 Excerpt: ...action of a bath of dilute ammonia in increasing the speed of an ordinary dry plate was applied to commercial panchromatic plates in the process worked out by S. M. Burka 11 and C. C. Kiess at this Bureau in 1918. They found that commercial panchromatic plates bathed for four minutes in--had the total speed increased 100 per cent and the red speed increased 200 to 800 per cent. A greater increase in speed was obtained by the use of 3.5 to 100 cc of water, with the omission of the alcohol. In this case, however, the plates dry more slowly and develop more fog than when alcohol is included in the hypersensitizing bath. A rinse in alcohol after the ammonia bath will help in drying the plates more rapidly. In an early investigation of the sensitizing properties of cyanin Schumann found that bathing in a dilute solution of ammonia imparted great speed and sensitivity to a plate with cyanin incorporated in the emulsion. (See Photographische Rundschau, 3, pp. 143, 175; 1889.) In Fig. 17 are shown the results of a keeping test made on Wratten Panchromatic Process, D. C. The plates were hypersensitized without the use of alcohol. The plates gave evidence of a slight increase in speed for a few days after hypersensitizing, Fig. 17.---Variation of speed and/og with time of keeping hypersensitized plates The fog has increased from a density of 0.4s to 3.00 in 45 days (a density of 3.00 transmits 1/1000 of the incident light). Note.--The fog is given for--1-3; that is, the development was carried until the contrast was twice that in the subject. while the fog kept increasing from the time the plates were hypersensitized. A comparison of the increase in speed brought about by washing and by hypersensitizing commercial panchromatic plates shows that a part of the hypersen...