Motion Picture Herald (Jan-Mar 1932)

February 27, 1932 MOTION PICTURE HERALD 73 TECIiNCLCGICAL The BLUEBOOK School By F. H. RICHARDSON BLUEBOOK SCHOOL QUESTION NO. 117.— (A) Why must the crater of the high intensity arc be much deeper than that of the ordinary arc? (B) Why is it possible to heat the high intensity gas to a far higher temperature than it is possible to heat carbon? (C) Of what is high intensity gas composed? (D) Why does the flame of a horizontal arc lean toward the negative carbon at low amperage, but swing farther and farther back toward the positive as amperage is increased? Answer to Question No. 113 Bluebook School Question No. 113 was: "(A) WJtat extremely important factor enters into all electrical action problems, particularly as concerns the production of light by electrical action? (B) Does the floor of the crater of an electric arc present a surface of even luminosity? (C) At the spot, the image of the crater floor, or other light source is inverted. Why is this so?" I find a goodly number of correct answers to this bunch of questions — also a surprising number who fell down flat in Section B. Those answering all three acceptably were : S. Evans and C. Rau*, Lester Borst* (also three excellent answers with no name attached— always place your name on the sheets containing the answer), Lewis Goldman, G. E. Doe*, Roy J. Arntson*, James J. Hobdell*, Bill Doe*, S. Evans*, James McGuire*, Pat O'Brien*, S. R. Anderson*, Tom Turk*, T. Van Vaulkenburg, James Davoy*, George Thompson*, John Williams*, Richard L. Lomax*, S. T. Jones*, Andrew McPherson*, Andy Bailey*, T. Wylie*, D. Hoatling*, Cyrus Wentworth*, John Flynn, Thomas Rodney, D. R. Robbins, John Tanney, James Dringe and Phillip Ball, H. G. Tonlin, J. T. Loat, D. L. Raildon, W. D. Samuels, Frank Sander, Dan Graby and Lon Shotts, Larry James, George Daniels, Frank Olliver, D. Lantry, James Young, William Sudbury and Tom Blanchard, Lewis A. Goldman, Frank Peters, D. L. Little, Dave Love, S. T. Jones and Frank Tubel, Henry Davis, T. L. Davidson, Tom Wignath, Tom Murphy, Bert Johnson, W. D. Singleton, O. Granby, Frank D. True, Andrew McPherson, William Edwards, K. L. Knight, William Bogert, P. H. Bondom, Harry Lidding, Sam and Andrew Wells, R. L. Little, A. Rnagor, F. G. Garrison, Mike McGuire, T. L. May, Dan Roxbury, Thomas McGruder, Abe Lichtman, John G. Farmann, John Cermak, Kent Garman, Sackman and Tracy, Henry Sicmann, William Broadbent and Chick Peters. (An asterisk indicates an especially good answer.) There are many excellent answers, but, after all, it seems to me that of James J. Hobdell is the most excellent and complete. He says : "A. — Resistance is an extremely important factor entering into all electrical action problems, especially in so far as concerns production of light. "In the incandescent lamp, light is produced by a continuous conductor (filament) of small diameter and high resistance. It is heated to high temperature by the current forced through it against resistance by voltage. The voltage consumed in forcing the current against the high resistance of the filament appears in the form of heat of such incandescence that it may be and is utilized for illumination purposes. "In the case of the electric arc, the conductor is not continuous. There is a short gap between the electrodes (conductors), and because of the resistance involved, the floor of the positive carbon is heated to a high degree of incandescence, hence becomes available for light. V "B. — The floor of the crater of an electric arc does not present a surface of even luminosity. When a cored positive carbon is used, the core is of a softer mixture than the outer shell and is vaporized with salts that vaporize at very high temperatures, thus presenting a surface of greater luminosity than is presented by the area of the crater immediatey surrounding it. "Impurities in the carbon also interfere with the actual even luminosity of crater floors, for the reason that they vaporize at higher or lower temperatures than normal and thus tend to alter the luminosity values of such points until the impurity has been burned out. "In the alternating current arc, unevenness of the crater floor is more pronounced than is the case in the d. c. arc, for the reason that there is a greater tendency for the arc to wander over the surface of the crater. In any carbon arc it cannot be expected that the entire crater floor will have exactly the same resistance at all times at every point of its surface. It then follows that the current flow and the temperature will not be exactly the same throughout the area of the crater floor, hence the luminosity of the area will vary. [Note : I'm not quite certain, and there is not sufficient time to ascertain the exact facts, but I think in his remarks about cores. Brother Hobdell had in mind the H. I. arc, though what he says is to some degree true of the straight arc as well. — F. H. R.] A "(C) The image of the crater (very much out-of-focus image, by the way) is inverted at the spot (cooling plate plane), due to the fact that the outer rays of light projected by the converging lens of the condenser, or the mirror, for that matter, cross at a point between the condenser or mirror and the cooling plate. Past this crossing point the image is, of course, inverted." The reason I like this answer is because it is quite complete. So many men answer correctly enough, but ink seems to be scarce in their locality, or they haven't many words to spare. Lester Borst, however, expanded his remarks in replying to Section B, as follows: "Practically speaking, the floor of an arc crater is known to be of even luminosity, provided, of course, the arc be operating at normal current values. As is known, no two parts of any carbon have exactly the same resistance ([Pretty broad statement — but maybe. — F. H. R.], hence theoretically the crater floor varies in luminosity. This is particularly true of the silicate low resistance core used in nearly all carbons. This means that the points of highest brilliancy on a crater floor will vary constantly as the carbon burns away. Considering the intense brilliancy of the crater floor, viewed as a whole, however, these variations in luminosity are, it seems to me, almost completely overshadowed and obliterated, though this would, I believe, only hold true when carbons of high quality are used." I believe what Friend Borst says is very largely correct. Theoretically and actually there undoubtedly are variations in every crater floor (I am not considering the core, but the shell floor only), but notwithstanding that fact, it seems to me these minor variations must be pretty thoroughly ob