International photographer (Feb-Dec 1929)

July, 1929 T I, INTERNATIONAL PHOTOGRAPHER Thirteen that they may be used for illuminating purposes. Plain carbons have always given some kind of a crater in the positive electrode, so that two of the elements of the H. I. arc are old in the art of illumination. The feature of the H. I. arc is the combination of luminous gas with a deep crater in which it (the gas) is momentarily confined and thus stabilized in space and emission of light. The component parts of the high intensity arc are: 1. ARC STREAM— The violet stream of carbon gas extending from the negative to within several mm. of the plane of the crater. 2. CRATER GAS — The light giving gas contained within and adjacent to the crater on the end of the positive electrode. 3. FLAME — The jet of gas formed by the combining of the gas streams from the negative and from the crater. Proper Position of Carbon In Figures 1 and 2 are shown the proper positions of carbons for different currents. It will be found that a different condition exists when a comparatively high current is used, than when a range of from 80 to 100 amperes is the case. As shown in Figure 1 a high current density in the negative carbon produces the blue tongue shown at 1, which can be used to advantage if positioned as shown. Figure 2 does not show this tongue as it is in the lower range. Explanation of the numbers is as follows: 1, negative tongue; 2, positive gaseous ball; 3, negative flame, and 4, positive tail flame. For lower currents the positive carbon will not project as far into the negative flame, or may even be out of it with satisfactory results. The operator should not use other carbons or combinations than those above mentioned and expect the operation of the lamp to be satisfactory. The lamps are designed to feed properly within these ranges. Light Used 25 amp. plain carbon arc 50 amp. H. I. arc 70 amp. H. I. arc 400 Watt 115V Mazda 1000 Watt 115V Mazda Carbons Two sizes of electrodes are used — these vary with the different amp. lamps used. (Studio lamps all burn at HOv). The shell of the positive is very hard and brittle and requires care in handling; the Brinell tests show that they are hard as mild steel. The core is heavily loaded with fluorides of Cerium and Thorium. These salts are used because of their selective radiation and under electrical conditions are extremely effective light radiators. The core of the negative is of soft carbon and the size considerably smaller than that of the positive, and for studio use is coated with either copper or an alloy to prevent penciling, and makes it a better conductor of current. The carbon gas generated is given off at a high velocity. This is a vital feature, for the proper maintenance of the arc depends upon the strength and stability of the stream of carbon gas to prevent flickers. Care must be taken in adjusting the electrodes of the arc because the light source is the small volume of gas contained within the crater; the light is dim or bright, according as the crater is full or empty; the steadiness of the light depends on the freedom from turmoil in the gas. The crater gas has the highest brilliancy. The flame is next, being composed in part of crater gas. The arc stream is the lowest, being identical with the arc stream from pure carbon electrodes. In comparing the H. I. arc with plain carbon and incandescent lighting, the H. I. arc is without peer and almost without competition, as is seen by the following test: H. I. arc B. C. P. 850 per sq. mm. of crater surface. Plain carbon arc B. C. P. 135 per sq. mm. of crater surface. Tungsten crimped ribbon filament B. C. P. 35 per sq. mm. of crater surface. The following test is conclusive proof in itself that the H. I. arc is here to stay with proper and careful operation. (D. C. is used in this test because A. C. gives a much lower beam candle power and is subjected to fluctuation and flickering). Beam Candle Power Flood 11,000 C. P. 25,000 C. P. 35,000 C. P. 5,000 C. P. 6,000 C. P. Spot 80,000 C. P. 750,000 C. P. 950,000 C. P. 13,000 C. P. 47,000 C. P. In using a 24-inch mirror behind a 150 amp. arc the beam candle power is approximately 150,000,000. A 60inch mirror develops 725,000,000 beam candle power. It is theoretic These sizes are standard national carbon and by many tests have proven the most efficient. Amps Kind Diam. Pos Diam. Neg. Coating Type of Arc 25 spot % 5-16 x 6 orotip carbon 35 twin-arc % x 12 V2 xl2 none carbon 35 spot % 5-12x6 orotip carbon 70 spot % x 6 11-32 x 6 orotip carbon 80 rotary % x 12 3/Rx9 orotip H. I. 100 rotary 13-6-10 mm 7-16 x9 orotip H. I. 120 spot 1x6 y2 x6 orotip carbon 135 rotary 16 mm X 20 7-16x10 copper none or H. I. 150 sun-arc 16 mm X 20 7-16x10 copper none or H. I. ally possible to boost this to over a billion and work is being done at the present time in re-designing the mirrors. All studio lighting equipment in spot lights is through condensers, which may decrease or increase the beam candle power, depending upon the accuracy and clearness of the lens. In conclusion it is my thought to bring to your attention the relative beam candle power per ampere between incandescent lights and carbon arcs. P. C. carbon arc 3,200 B. C. P. per amp. H. I. arc 15,000 B. C. P. per amp. Incandescent lamp 4,700 B. C. P. per amp. Therefore, we find, that a 3,000 watt incandescent spot pulled down hot gives you a beam candle power of 131,000. An 80 amp rotary spot at flood gives you 40,000 B. C. P., and pulled down hot approximately 1,200,000 B. C. P. A 20 amp plain carbon spot at flood gives you 52,800 B. C. P. and on spot 384,000 B. C. P. If you are looking for the nearest substitute for noon-sunlight and a maximum beam candle power per lamp we should think that the 80 amp. rotary spot, the 24-inch sun arc with 2,250,000 beam candle power on the candle power of 144,000 should be the light that you would use. THE S. M. P. E. By HERFORD TYNES COWLING The basis of modern business is manufacture controlled by scientific research and sound engineering practice. Experience has shown that no business can create all its own technical knowledge but must co-operate and exchange ideas with allied organizations. This vital interchange can be secured most easily by membership in the appropriate engineering society. The motion picture industry may claim that more sciences are involved in making its products than contribute to any other manufacture. Consequently, the motion picture technician has been forced to join a number of scientific societies or else remain sadly behind the times. To remedy this condition by guiding all the diverse material with one channel, the Society of Motion Picture Engineers was formed in 1916. In the words of its constitution the society saith: "The advancement in the theory and practice of motion picture engineering and the allied arts; the standardization of the mechanisms and practices employed therein, and the maintenance of a high professional standing among its members." That this object has been happily realized is apparent from its large and growing membership, and from its published Transactions, which present a library of motion picture science unrivalled in completeness. The society is composed of two classes of members, "Active" and "Associate," <Jrawn from the best technical personnel of studios, factories, and research laboratories throughout the world. The society's (Concluded on Page 24)