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.
DRY PLATES, FILMS AND PAPERS
The ordinary dry plates may be divided into groups according to their sensitivity to the action of light, those which are least sensitive being termed slow, and then with increasing degrees of rapidity we have medium, rapid and very rapid plates.
The Emulsion for Dry Plates. — In all these plates a gelatine coating is used, ammonium bromide and potassium iodide being dissolved up in distilled water with the gelatine. A second solution is made of silver nitrate in distilled water, to which is added sufficient ammonium hydrate to dissolve the precipitate first formed.
The second solution is added to the first either in the cold state if slow plates are required, or the first is kept at a temperature of about 120° F. while the second solution is added as when more rapid plates are required. The rapidity of the plates depends to a large extent upon the relative amounts of gelatine, bromide, iodide and nitrate present, but it also depends upon the treatment which the solutions undergo before and after mixing.
A digestion of the solutions at about 130° F. for about one hour will greatly increase the speed of a plate over one similarly coated, but the gelatine, etc., of which has not been digested at such a high temperature.
For ordinary photographic purposes the slow plates will be found quite satisfactory ; it is quite possible in good lights with lens aperture //16 to use these for making snapshots of objects. Of course, for focal plane work and the photography of rapidly moving objects it is better to use some of the more rapid varieties.
No attempt, however, will be made to describe any
]59