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peres at the arc for screen areas of 400 sq. ft. are common and even 150 amperes (10 kw.) are being tried. Couple these arc wattages of 7 kw. and 10 kw. with the fact that 60 inch searchlights require only 14 kw. we have some conception of motion picture projection and what it is coming to if present rate of improvement keeps up.
Knowing the amount of current after analyzing theater lighting, screen and equipment requirements, we can select the size of carbons to produce satisfactory screen projection.
Below are given the proper carbon combinations for the different current requirements and also the standard settings for both direct and alternating current projection.
CARBON COMBINATIONS
DIRECT CURRENT
Current Size Carbons
For 25 to 50 Amps. D. C. use
5/8 X 12 inch Cored Upper
5/16 X 6 inch Metal Coated Solid Lower
T? ^^.^/c^A r\ n i 3/4 X 12 inch Cored Upper
For 50 to 65 Amps. D. C. use \i,}^^^^ -^^^ Metal Coated Solid Lower
T? ^^ ^ „ /K T\ n / 7/8 X 12 inch Cored Upper
For 6s to 70 Amps. D. C. use [ [^^^^ ^ ^ j^^j^ ^etal Coated Solid Lower
T? ^.o.A x\ r (7/8x12 inch Cored Upper
For 70 to 85 Amps. D. C. use [ ^/g ^ ^ j^^j^ ^etal Coated Solid Lower
T? 0 . . A T\ n (1x12 inch Cored Upper
For 85 to 100 Amps. D. C. use \ ^^^^ ^ ^_ j^^j^ Metal Coated Cored Lower
ALTERNATING CURRENT
Amperes Carbon Diameter
40 or less than 60 5/8 inch Combination
60 or less than 75 3/4 inch Combination
75 or less than 100 7/8 inch Combination
Projector Carbon Manufacturing Process In the manufacture of high-grade projector carbons it is necessary to use an especially prepared carbon flour. The flour is carefully mixed with the necessary binding material and forced by hydraulic presses under high pressure into the desired shape. If a cored carbon is wanted, a steel needle is suspended in the center of the die. The forced carbons are then placed on racks to cool and when sufficiently cool they are cut in the proper lengths for baking. To insure absolute straightness, correct size and perfect stock before baking, the cooled carbons are thoroughly inspected before being turned over to the baking department.
In the furnaces, the carbons are subjected to the temperature necessary to produce a uniform carbon of certain definite prescribed qualities. After the bake is completed, the furnace is sampled and the carbons examined by the testing department before being sent along for finishing. These tests are even more severe than those to which a projector carbon is subjected by the user.
Upon receiving the testing department's O.K., the carbons are sorted for straightness and examined for imperfections, and if they are hollow shells, made ready for coring. Every precaution is taken in the coring department, where the hollow shells are filled to see that the
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