The Embryo Electrical Engineer Some Sound Advice Based on Experience NE OF THE a young man what course to pursue in order to become an electrical engineer, the means for taking a collegiate course not being available; also to suggest the best branch of electrical work. It is, of course, impossible for us to offer much specific advice in such cases; without knowing intimately a young man's natural characteristics, one cannot intelligently suggest what avenue of work would be apt to suit him best, and there is no "best branch" of the electrical industry from any other standpoint. Naturally, we advise taking up a course of study with some correspondence school, if one cannot have the advantage of personal tutelage; and when this is said, it exhausts the possibilities in the way of specific advice under the circumstances. Generally speaking, technical education is absolutely necessary to even mediocre success in any branch of electrical or other technical work; with a given amount of honesty, intelligence, and industry, the better the education, the greater the measure of success. By "education" we do not mean necessarily college advantages, valuable though they are; some of the highest-grade men in the electrical field are self-educated, and some of the most hopelessly incompetent boast college degrees. With the facilities that now exist for acquiring technical education, there is no excuse whatever for anyone to remain wholly ignorant of fundamental principles and their application. But the road to complete qualification as an electrical engineer is not an easy one; and while there is always "room at the top," there is no room in the class of the poorly qualified-no demand for the mediocre engineer. If one elects to become an electrical engineer, therefore, the standard should be set very high; and the aspirant must determine to sacrifice everything except personal character, if need be, to the drudgery of acquiring the necessary mental training and practical experience. These may possibly be acquired simultaneously, but it is usually necessary to obtain the mental training first. Detailed advice as to just what steps to take in order to secure the requisite knowledge and experience is out of the question; a man's resources, environment, and restrictions chiefly determine this, and these are seldom combined in the same way twice. Moreover, a man who possesses the personal qualities essential to thorough success does not require to be steered along from point to point in his upward course.-American Electrician. ONSVLTING DEPARTMENT In order to receive attention, all inquiries must be addressed to the Consulting Department, and must be accompanied with the full name and address of the sender. In view of the fact that the inquiries already received have far exceeded the available space, the Editors reserve the right to select for publication only those inquiries likely to be of greatest interest to the readers of the magazine in general. Other inquiries will be answered by letter. Gas-Engine Indicator Diagrams Question: Please explain how to calculate a theoretical indicator diagram for a gas engine when the cylinder, diameter, stroke, and volume of clearance only are known. Also, how to calculate volume of clearance required, when the diameter, stroke, and desired compression, gauge pressure, only are known. An answer to the above would be of great service to me, especially if it can be done without using logarithms.-F. A. D. Answer: The mathematical formulæ appertaining to the computation of the element of heat, and its work in an explosive engine, are in a large measure dependent upon assumed values, because the conditions of the heat of combustion are made uncertain by the mixing of the fresh charge with the products of a previous combustion and by absorption, radiation, and leakage. The theoretical diagrams can be laid out by assuming the compression and expansion to be adiabatic. Assuming the action to take place as stated, approximate cards can be drawn, but results of any value cannot be obtained without the use of logarithms. The relation of pressure and volumes is expressed by the formula P V1.41 P,V,1.41 By plotting pressures vertically and volumes horizontally, different points on the curves of compression and expansion. can be found and laid out to the scale assumed. At the end of the stroke we know the total volume, and the pressure is that of the atmosphere. Then at 2 of the return stroke, the volume will be 2-3 of what it was at the beginning, if the clearance is 1⁄2 the total piston displacement. Calling the original volume I, the volume at half stroke would be 2-3. The original absolute pressure is 14.7 pounds. Then in the formula given above we have: From this, PX (2) 1.41 14.7X11.41 P=14.7X()141-14.7 × (1.5)1-41 This is easily solved by logarithms, for we have: Log P=log 14.7+1.41 log 1.5. Knowing the logarithm of P, P itself can readily be found. In the second case, we have to find the volume when the pressure on the compression curve has risen to a certain amount. The original pressure and volume may be called P and V respectively, P being 14.7. The final pressure and CONSULTING DEPARTMENT--(Continued) volume are P1, which is given, and V-S, V being the same as before, and S the piston displacement, which is known. These values can then be substituted in the formula given above, which is solved as before. Effect of Ground-Need of Insulation Question 1: Will a heavy ground on the primary line of an alternator open the main circuit-breaker? Question 2: Is it necessary to place some kind of insulating material between the subbase of an alternator and the foundation stone?-L. H. Answer 1: If the machine or circuit is not otherwise grounded than at one point, the main circuit-breaker will not open; in other words, there must be a ground on each side of the line in order to cause a short-circuit and throw the circuit-breaker. Answer 2: This can best be decided by referring to the Underwriters' rules on this subject, which read as follows: "Generators must be thoroughly insulated from the ground wherever feasible. Wooden base-frames used for this purpose, and wooden floors which are depended upon for insulation where for any reason it is necessary to omit the base-frames, must be kept filled, to prevent absorption of moisture, and must be kept clean and dry. "Where frame insulation is impracticable, the Inspection Department having jurisdiction may, in writing, permit its omission, in which case the frame must be permanently and effectively grounded. "A high-potential machine, which, on account of great weight or for other reasons, cannot have its frame insulated from the ground, should be surrounded with an insulated platform. This may be made of wood, mounted on insulating supports, and so arranged that a man must always stand upon it in order to touch any part of the machine." Testing Rivet Steel Question: Please inform me through the columns of THE TECHNICAL WORLD, as to what is the way of testing a piece of rivet steel at the forge.-D. R. B. Answer: There is a great lack of uniformity in the rules prescribed by differ ent writers and by legislation, for testing rivet steel. All materials entering the construction of boilers for marine vessels must be constructed according to the regulations prescribed by the Board of Supervising Inspectors of Steam Vessels. The Board of Trade rules regarding rivet steel are as follows: The tensile strength of rivet bars. should be between 26 and 30 tons. Elongation in 10 inches not less than 25 per cent, and the contraction of area not less than 50 per cent. Lloyd's rules, tensile strength 26 to 30 tons, elongation not less than 20 per cent in 8 inches. The material must stand bending to a curve the inner radius of which is not greater than1⁄2 times the thickness of the plate after having been uniformly heated to a low cherry red and quenched in water at 82° F. Another test requires that the rivets. shall be capable of being flattened out cold under the hammer to a thickness 1⁄2 the diameter, and of being flattened out hot to a thickness of 1-3 the diameter, without showing cracks or flaws. Boiling Point of Gasoline Question: I am interested in the gasoline engine, and should like to know the answers to the following questions: I. How many cubic inches of gas, at atmospheric pressure will a cubic inch of gasoline generate, providing the temperature remains constant? 2. At what temperature will gasoline boil at atmospheric pressure? 3. How many cubic feet of air at ordinary temperature and atmospheric pressure are required to completely burn one cubic inch of gasoline? 4. What is the increase in pressure of a properly proportioned charge of air and gasoline?-H. P., Jr. Answer I. The vapor of commercial gasoline at 60° F. is equal to 130 volumes of the liquid. 2. Gasoline boils at from 140° to 158° F., depending upon its specific gravity. The higher the specific gravity, the higher will be the boiling point. 3. Since the ordinary gas requires about 9 volumes of air for its complete CONSULTING DEPARTMENT-(Continued) cases it would not seem advisable to connect up to the city mains. In other words, the heating system should be distinct, an expansion tank being used to take care of the increase in volume. If connected to the kitchen tank it would probably interfere with the water back. Answer 2: While it may not be absolutely necessary to have every part of the coil in the furnace above the point of entrance, yet it would certainly be best to have a constant pitch upward. The mains are always inclined upwards from the heater, and the returns inclined downward and connected with the heater at the lowest point. Relation of Armature Current and Load Question: How is it that the amount of current which the armature of a direct-current motor takes, depends on the load applied at the pulley?-B. E. J. Answer: The electric motor is automatically self-regulating with respect to HOT WATER CIRCULATION SYSTEM. Answer 1: We give, in the accompanying sketch, the best of the two plans you have submitted. The circulation of hot water in any system depends only on the difference in temperature of the water in the supply and return pipes, since the greater the difference in temperature, the greater the difference in weight, and circulation is due to the pressure caused by the difference in weight. The circulation can be obtained in either way, but for most the amount of current it takes for a given load. If we increase the load, the current automatically increases; and if we decrease the load, the current automatically decreases. If the load is increased, the speed drops and the counter-E. M. F. decreases which allows the current to increase until the required torque is obtained. It is also evident, from the law of conservation of energy, that the current must increase with the load, otherwise the motor would be giving out a |