We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
112 CINEMATOGRAPHIC ANNUAL
circle; the next opening had an angular aperture of 90°, or one quadrant; the next of 45°; the next 22J/2 °, and so on, the angular aperture of each successive opening being halved until nine openings were reached. A diagram of the original Hurter and Driffield sector wheel is shown in Figure 1.
Later on this sensitometer was remodelled and consisted of a rectangular box about three feet long at one end of which was a lamp house which contained a burner using pentane gas. The other end of the box contained the sector wheel and a slot to receive a plate holder in which strips of the unexposed plate were placed for exposure. The exposure was actually accomplished by removing the dark slide of the plate holder and by mechanical means revolving the disk which was in front of it. As aforestated, the disk contained nine angular openings, decreasing by a factor two from the maximum opening of 180°. This gave an exposed sensitometric strip, which in present day parlance we would refer to as "an exposure of nine power of two steps."
The next step in their procedure was the development of the exposed plate. Up to this we have not discussed the researches of Hurter and Driffield as regards development. It will suffice to say that prior to their investigations pyrogallic acid was found to be a reducing agent for light struck salts of silver, especially the nitrate salt. The developer itself was made up of pyrogallic acid, ammonia, and ammonium bromide. Later experiments showed the use of a ferrous oxalate developer. It is interesting to note that they made investigations of varying amounts of chemical constituents used and in Table 1 is given the formula for one of the many developers made up by them.
TABLE I
Developer, 100 cc contain 0.085 g. of NH3 0.400 pyrogallol 0.250 NH4 Br.
A formula for a ferrous oxalate formula is given below as a matter of interest.
Solution A
Potassium Oxalate 750 grams
Water to 2250 ccs
Solution B
Ferrous Sulfate 250 grams
Sulfuric Acid 10% 15 ccs
Water to make 750 ccs
For use; 1 ; 1