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.
362 RICHARDSON'S BLUEBOOK OF PROJECTION
arc is formed, are called carbons, although they contain other materials beside carbon, and are often coppercoated. Carbons are classified by trade names, by their length, and by their diameters. Carbon diameters are very often stated in millimeters (mm). One mm is 0.03937 of an inch, hence millimeters may be reduced to inches by multiplying the mm diameter by 0.03937. Thus a 12 mm carbon would be 12 X 0.03937 = .47244, or about one-half of an inch in diameter.
Carbons used in modern motion picture projection work must have certain well-defined qualities. (12) They must, within very narrow limits, be straight, uniform in texture and, except for the core, of uniform density throughout. They must, to all intents and purposes, be entirely free from impurities. They must, within very narrow limits, be made in exact diameters, each diameter suited to a given range of current flow. (13) Their cores must contain certain materials, some of them chemically rare, the exact composition of which is determined by the uses to which the carbon is to be put. (14) Carbons must be free from all moisture at the time they are used or results will not be the best.
(15) Carbon was selected as the base for arc lamp electrodes because it is the one available material able to withstand the action of heat up to (16) approximately 3,500 degrees Centigrade, at which point it is finally "volatilized," that is, transformed into gases except for a very small residue of ash. (17) At such temperature it is very briliiant. In fact the luminosity produced is second only to that of the sun itself. Carbon may be reduced to a very fine powder, mixed with available, relatively cheap binders and moulded into rods of exact diameter having sufficient strength and rigidity to serve all the needs of practical projection work.
(18) In the form of finished rods, carbon possesses fair conductivity which, contrary to the action of metallic conductors, increases as its temperature is increased.
(19) In the process of manufacture a central opening of required shape and diameter is provided, later filled in with a core mixture of such nature that the core conduc