flame disappears. If no flame shows, turn lever anti-clock-wise until flame appears, then turn lever back until the flame disappears as above. Now move air-shutter slowly back and forth, watching the illumination given by the burner on a sheet of white paper placed underneath it, until the point of maximum illumination is found. With the adjustments so made, the greatest possible amount of light is being attained from the burner. Excess of gas can always be detected by the appearance of a tip of flame above the top of the mantle, the hand being held so as to shade the eyes. Deficiency of gas shows by the decrease in light, as will also a large excess of gas. Excess of air will be shown by the flickering of the light; deficiency of air by the blackening of the mantle in the absence of an excess of gas. (Trustees.) II. What causes an atmospheric burner to "light back," and to what is due the odor given off when this occurs? Ans. An atmospheric burner "lights back" whenever the speed with which the mixture of air and gas travels through the tube is slower than that at which a flame can spread through the mixture. Anything which decreases the rate of flow of the mixture of air and gas, or which increases the speed at which the flame can spread, will, therefore, tend to produce "lighting back." Some of the causes of a slow speed of the air and gas mixture are a large tube area, the issuing of the gas from the gas orifice at a low velocity because of being under a low pressure, and any draught or concussion of the air that creates a pressure at the point of ignition. The rapidity with which the flame can be propagated back through the mixture, depends upon the proportion in which air and gas are present, being greater the more nearly the amount of air present approaches to that required for the complete combustion of the gas. "Lighting back" may, therefore, be brought about by the gas being at too low a pressure, by a draught, or a sudden wave of air, such as that produced by the violent closing of a door, or by poor design in the burner, either in the way of providing too large a tube, or of permitting the drawing in of too much air for the amount of gas used. When "lighting back" occurs the gas burns as it issues from the gas orifice without being previously mixed with air, and consequently a luminous flame is produced. The conditions under which this flame burns are extremely unfavorable for the attainment of the complete combustion of the gas, because, not only is the access of air to the flame extremely restricted, but the flame is also surrounded by cold surfaces, and is extinguished by contact with them before complete combustion can take place. The combustion has, however, proceeded to a point at which the decomposition of the hydrocarbons has begun, and as one of the first steps in this decomposition is the formation of acetylene, C2H2, the products of the arrested combustion contain an appreciable percentage of acetylene, and it is to this gas that is due the distinctive odor noticed whenever an atmospheric flame is allowed to burn after having "lighted back." The products of this arrested combustion also contain carbon monoxide, and are, therefore, poisonous. (Trustees.) 12. In what part of the masonry or brick work of a gas works would you use cement mortar instead of lime mortar, and why? Ans. Cement mortar should be used in all thick walls, in all masonry subject to vibration, and in masonry exposed to water or moisture. It should, therefore, be used in the foundations of buildings and machinery, and in holder tank walls. Unlike lime mortar, good cement mortar increases in strength with age even under water or exposed to moisture— exposure to which will disintegrate lime mortar rapidly. When cement is cheap it is a question whether it could not profitably be substituted for lime in the mortar for even ordinary masonry. Its cost for such purpose when great strength is not required may be reduced without serious loss of strength by the addition to the mortar of from 20% to 25% of lime paste. (Trustees.) I. 2. 3. 4. 5. NINTH SERIES OF QUESTIONS-SECTION OF 1907— LIGHT ASSOCIATION. When using gas oil as the carburetting material in a double superheater carburetted water gas apparatus, should the checker bricks be kept at the same temperature in both the carburetter and superheater? If not, in which vessel should the highest heat be carried? Give the reasons for your answer. It is desired to "let down" a bench of coal gas retorts heated by a regenerative furnace. What is to be done in order that the bench may, with safety, be cooled down and kept idle until the increasing demand for gas, or other reason, shall make it important to again fire it up? No repairs are to be made to the bench. Give a description, illustrated with sketches, of some form of furnace for horizontal tubular boilers adapted to give a good evaporation per pound of gas coke. Give a drawing showing, by a section through the centre lines of the bent pipes, the layout for the bells on the mouthpieces and for the bent pipes for a bench containing six retorts, of the cross section given on the cut accompanying the answer to Question No. 2, Second Series, set in two vertical rows of three each, the centres of the retorts in each row being 2′ 3′′ from the centre line of the bench and 2' o" apart vertically. The pipes are to be 7" in diameter. The hydraulic main is 9' 934′′ long over all and has a 3" angle iron at each end, the space between these angles being 9' 34". The drawing must be fully dimensioned. Give also a written explanation of your reasons for adopting the design shown. A boiler using a fuel with a calorific value of 13,800 B. t. u. per pound is shown by a test to be evaporating 8.5 pounds of water per pound of fuel used. The water is fed to the boiler at a temperature of 15° F. and the gauge pressure is 95 pounds. What is the efficiency of the boiler? Give your calculations. 6. Describe some method of making iron oxide to be used for the removal of sulphuretted hydrogen from gas during its purification. 8. 7. How would you make quantitative tests for carbonic acid and sulphuretted hydrogen in gas? How much by volume of each would you expect to find in coal gas and in carburetted water gas at the inlet to the purifiers? If you had a set of purifiers consisting of four 12′ × 14′ X 4' boxes in which you wished to use oxide of iron in one layer 3' 0" deep in each box, how many bushels of oxide would you buy, or make up? The amount given should include not only the oxide actually in the boxes at any one time but also that which it would be necessary to have on the floor at the same time, to make it certain that each lot of oxide would be afforded the opportunity for complete revivification. Give the rea sons for your answer. 9. How does the calorific value of gas affect the consumption per horse power in a gas engine and what do you consider a fair average rate of consumption per brake horse power for a 10-horse engine using a gas having a net calorific value of 600 B. t. u. per cubic foot? IO. II. 12. If you were sent to a house to investigate a complaint of An instantaneous water heater burning gas at the rate of Describe the proper method of laying brick in holder tank (Answers to these questions are due April 23, 1906.) ANSWERS TO NINTH SERIES OF QUESTIONS-SECTION OF 1907-PRACTICAL CLASS-AMERICAN GAS LIGHT ASSOCIATION. I. When using gas oil as the carburetting material in a double superheater carburetted water gas apparatus, should the checker bricks be kept at the same temperature in both the carburetter and superheater? If not, in which vessel should the highest heat be carried? Give the reasons for your answer. Under ordinary conditions, the best oil efficiencies are obtained by carrying the checker bricks in the carburetter at a higher heat than those in the superheater. The reason for this is that a high initial heat seems to be required for evaporating the oil and breaking it up into permanent gases, while these gases, after their formation, should pass as soon as possible into a somewhat lower temperature, since the heavy hydrocarbons or illuminants will be deteriorated by further breaking down if they are subjected to too long an exposure to the high temperatures at which the oil is best broken up. (Trustees.) 2. It is desired to "let down" a bench of coal gas retorts heated by a generative furnace. What is to be done in order that the bench may, with safety, be cooled down and kept idle until the increasing demand for gas, or other reasons, shall make it important to again fire it up? No repairs are to be made to the bench. Ans. In letting down a bench of retorts with full depth regenerative setting, the last charge should be made as large as the retorts will hold. That is, if the charges are of four hours' duration and the bench is to be let down at 7 o'clock, the charges from 3 o'clock on should be made to almost fill the retorts. The coke from these charges must not be drawn until the bench is cold. The furnace should be left half full of coke. When the last charge is put in, the primary airslides should be shut down to within 1⁄2" of being closed, secondary air shut off entirely and the dampers closed until there is just sufficient opening left to maintain a slight draft |