the more quickly of the two. Or, we may look at it thus: When A has exhausted such an amount as will bring its pressure down to 25 pounds, it is then only in the condition that B was at the start, and B has been exhausting right along also. Evidently, then, A cannot catch up with B; in other words, B will discharge its contents first. If the cut-off and the design of the valve are the same in each case, the back pressure and the compression will be greater in A than in B. In A the pressure at cut-off is greater than in B, and, the exhaust opening at the same time, the pressure at that point is greater also. Thus, the back pressure is greater throughout the return stroke. Again, as the exhaust closes at the same time as in B, the compression is also greater. In each case, the same volume of steam is bottled up, but it is at a higher pressure, and therefore there is a greater weight of it in the one case than in the other. * ** (539) If a monkey sits on top of a post, and a man walks around the post, the monkey all the while keeping his face towards the man, does the man walk around the monkey? L. G. R., St. Louis, Mo. ANS.-Yes. In walking around the post-which you will grant the man does he also walks around everything that is on the post. ** (540) The enclosed sketch shows how I must fasten the bonnet to a strainer by means of the malleableiron yoke Y. Can you tell me how to calculate the dimensions A, B, C, and D? L. P. M., Philadelphia, Pa. ANS.-We will first deal with the stress at A, calculating the required section at that point. The screw measures 1 inches in diameter; the pitch therefore is inch, assuming it to be a standard thread. While the handle H rotates once, the screw descends through of an inch, and correspondingly for smaller movements of H. Assume the greatest effort likely to be imposed on H to be 20 pounds, and 10" H 5 .75' If we take b as inch, then d2 = or d = y 6.67 =2.58, or, say, 2 inches. Hence, the section at A is 2 in. Xin. We will now deal with the section at C. Having found A and C, the outline of the yoke may be put in by eye. At C, then, is a tensile stress distributed over the section, due to pull of screw. There is, in addition, a bending action, due to the pull not being in line with C but to one side of it; the tendency of this is to straighten the yoke out, in the same way that a crane hook tends to straighten out under its load. The stress at C, due to the dead load 1,250 (the pull of screw) is denoting the breadth and bd depth by b and d, as in the case of A. The stress due to bending is a tensile one at m, and a compressive one at n, the net effect being an increase of the pull at m, and a decrease of that at n. The distance between p and the center of section at Cis, say, 24 inches. We must bear in mind the clearance between the yoke and the flange. We already have an idea of what the width of C will be-judging from that of A-and we locate its center accordingly, and thus obtain its distance from p. If, on working out, the calculated width should prove too great to obtain the necessary clearance, we could set the yoke out a little, and make it a little wider, or else recalculate. The moment of inertia of the section is, as before, bd, the induced stress at m is screw. 1,250 17,750 1,250 d + 17.750 b d b d2 bd2 Equating this to the allowed fiber stress, and simplifying, we have 12" or, 10′′ HOME STUDY applied at a point 8 inches from the center of the As to the loss of power through friction of the thread in the yoke, and of the point of screw on the bonnet, we will assume it to be 65 per cent.; that is, .35 of the power exerted is available in tightening up. We then have 8 × 2 × 3.1416 X 20 X .35 = 4 × x, where x is the force in pounds with which the screw presses down on the bonnet. From the above we find that x=2,463, or, say, 2.500 pounds. Half of this amount comes on each foot of the yoke. Now, the 1,250 pounds at the end D may be regarded as all applied at the point p. 54 inches from the center line 11. The section A is, say, 14 inches from 11. The distance from p to A is therefore 4 inches. The stress 6,000 bd21,250 d 17,750; 25bd2-5 d=71. Solving this quadratic we find d= 2.08, or, say, 21 inches. The section at C is, therefore, to be 24 in. x in. The yoke can now be finished by eye. It is advisable to make the foot wider than the body of the yoke, to give it more stability-more especially as the yoke is a casting and not a forging. That is. make the part p, where it takes its bearing on the flange, about 14 inches wide, running it off-not too abruptly-into the 3-inch body. * ** (541) Kindly answer the following questions, and in each case give me what rules and formulas you can: (a) Studs 14 inches in diameter are to be used for securing a cylinder head; the steam pressure in the cylinder is 90 pounds per square inch; the stress per square inch of section in the studs must not exceed 1,800 pounds: How many studs will be required? (b) If a cylinder head is secured by means of twentytwo 14-inch studs, and the pressure of steam in the cylinder is 90 pounds per square inch, what must be the diameter of the cylinder in order that the stress per square inch of section in the studs shall be 1,800 pounds? (c) A crown sheet is 6 ft. 6 in. x 9 ft. 9 in.; it is subjected to a steam pressure of 90 pounds per square inch. What is the total pressure on the plate? (d) A 44-inch safety valve must blow off at 85 pounds steam pressure; I wish to use -inch steel for the helical spring. What must the outside diameter of the spring be? (e) A brace 2 inches wide by & inch thick is fastened to a boiler plate by 4 rivets; the steam pressure is 65 pounds gauge. What must be the diameter of the rivets? () What is the greatest allowable pitch for 14-inch stays in a boiler working at 60 pounds gauge pressure? (g) How is the length of a connecting-rod found? M. M., Duluth, Minn. ANS.-(a and b) The stress you limit yourself to is very small. If the studs are of steel you may allow a working stress of 5.500 pounds per square inch of net sectional area; if of wrought iron, allow 4,500 pounds. The area in question is that taken at the bottom of the thread; for a 14-inch thread this area is .893 square inch. You do not give diameter of cylinder in (a). Let D= diameter of cylinder in inches; A area of cylinder head in square inches; P = steam pressure in pounds per square inch: sectional area of stud at bottom of thread in square inches; a If both cylinder covers are on and screwed up, bump the piston up at each end alternately, and mark the position of crosshead on the guides. Deduct the required clearance at each end of stroke, and bisect the remaining length. Set the crosshead to this point. Then the piston is at half stroke. Take an adjustable train with one bent leg, and set to the center of crosshead pin and to the near face of shaft. Add half the diameter of shaft at this point, and the sum will be the length of rod required. If the shaft is not in place, stretch a line through the main bearings, and obtain the distance from the center line to the center of crosshead pin. If the measurement is taken from the face of the crosshead pin, add half of its diameter. (542) I enclose sketch of a steam separator, Fig. 1, showing the spiral around a cylinder. Kindly show how the layout of the spiral is made. Take, for Formula (1) will give what you want in (a), while (2) will do for (b). (c) Multiply the area of the sheet by the pressure on a unit of the surface. Area in square inches = 78 X 1179,126. Total pressure on sheet = 9,126 X 90=821,340 pounds. (d) Let A = area of valve in square inches ; P = steam pressure in pounds per square inch; d = diameter of spring steel: D= diameter of coil of spring (reckoned from center to center of the wire). Then the formula D= 8,000 da AP may be used. In your The outside diameter will be inch more than this. (e) The steam pressure tells us nothing, as you do not say how much surface the brace has to support. Neither do you say whether or not it is set at any angle, as when the boiler head is stayed to the shell. We shall simply assume that the rivets are to be such that there will be uniform strength throughout, that is, in them and the brace. Doing this, and further assuming the shearing strength of the rivets to be four-fifths of the tensile strength of the brace, we find that 14-inch rivets, in single shear, would be required; that is, 1-inch rivets in 14-inch holes would do. This will allow only inch on each side of the rivet hole, however-not enough with this size of rivet and thickness of plate. If a wider brace cannot be used, make it thicker. (f) We presume you allude to the longitudinal stays. You say nothing as to size of boiler or thickness of plate. Assuming the latter to be steel and inch thick, and the stays fitted with nuts, you may use a pitch of 13 inches. (g) We suppose you want to know how to find what length the connecting-rod requires to be. FIG. 1. example, a cylinder 12 inches in diameter, spiral belt 6 inches wide made of steel plate inch thick. and let the pitch be 12 inches. 12.6 H. M. L., Pottstown, Pa. ANS. The circumference of the cylinder being 12 X 3.141637.7 inches, the length of the helix for one turn around the cylinder is 37.7 +12= 39.563 inches. This must be equal to the inner circumference of the annular plate, Fig. 2; hence, the inner diameter is 39.563 inches ÷ 3.1416 12.6 inches. In a similar manner, the outer diameter is found to be 18.4 inches. Since a screw surface is not developable, the plate must be hammered, or peened, when stretched along the cylinder. The stretch due to the hammering will be greatest at the outer edge, and will gradually diminish to nothing at the inner edge. -18.4" FIG. 2. HOME STUDY (543) (a) I wish to compress sufficient air to run a 4-horsepower engine for one-half hour at a time. How large an air cylinder will be required? (b) What is the motive power generally used on horseless carriages? E. C. F., Rochester, N. Y. ANS. (a) We suppose you refer to the storage cylinder. If you compress to 500 pounds per square inch, a cylinder 20 inches inside diameter and 42 inches long will suffice. As you will use the air in the engine at a much lower pressure, say 80 pounds, you will require a reducing valve. If you compress to a lower pressure than the above, you will, of course, require more storage space, which may or may not be convenient to you. (b) Electricity, by means of storage batteries. A prominent firm in this country started in this work in August, 1895. The first carriage made was one run by electricity. They were about 18 months before putting it out publicly, and it was a success. At the same time they were working on a gasoline carriage, and this is not out yet. So far, builders certainly seem to have been more successful with the electric motor. A good many builders believe in steam. It is possible, however, that in the future compressed air will play a great part in this line of work. The same objection applies to that as to electricity: it is impossible to renew your power if away from the ordinary sources. This is why builders are trying to make a success of gasoline and steam, since the supply of oil, coal, and water may be renewed wherever one may be. * * * (544) (a) Is there any rule for determining the size of air chamber on pumps working against pressure? (b) If there are any special points in the construction of air chambers, please give them. (c) Can you give a rule to find how much larger than the cylinder a piston ring should be turned, in order to give them the proper spring? What should be the width and thickness of rings? W. B. E., Downesville, Pa. ANS. (a) For double-acting single pumps, the air chamber should have a capacity three times that of the pump-piston displacement, that is, during one stroke. If for higher pressures and speeds, as in fire engines, make the capacity twice the above amount, that is, six times the displacement of one stroke of the piston. If the pump is a double-acting duplex, use a capacity from five to seven-tenths of the above. (b) Set the air chamber on the highest part of the pump, and, in every case, above the highest portion of the delivery opening. Keep the diameter of the neck as small as practical considerations allow. (c) It all depends on the section of the ring. The stiffer the ring, the less the difference need be between its original diameter and that of the cylinder. For an 18-inch piston, use two rings inch wide and inch thick. Turn to 18 inches in diameter and cut out 1 inch of the ring. For 13-inch pistons turn rings 13 inches in diameter, and for 6-inch pistons turn them 64 inthes in diameter; other sizes proportionately. See HOME STUDY FOR MACHINISTS, STEAM ENGINEERS, ETC., August, 1897, article entitled "Piston Rings." * ** (545) Kindly explain the principles of nickelplating. Also give instructions for making a small plant for nickel plating and for giving the copper bath. G. S., St. Augustine, Fla. ANS.-HOME STUDY FOR ELECTRICAL WORKERS, July, 1898, article entitled "Electroplating," will give you the required information with respect to the apparatus necessary for plating, and its manipulation. The copperplating bath may be prepared by taking 20 parts acetate of copper, which is made into a paste by addition of a little water; to this is added 20 parts carbonate of soda crystals dissolved in ten times as much water, the whole being well stirred. 20 parts bisulphite of soda is then dissolved in 200 parts of water and added, and subsequently 20 parts cyanide of potassium dissolved in 600 parts of water is added. If the bath is not clear, add more cyanide. The nickel bath is made in the proportion of 12 to 14 ounces double sulphate of nickel and ammonia to 1 gallon of water. To give a bright finish to nickel work, the objects must be buffed on a polishing lathe. A wire scratch brush is used for this, and may be obtained of any large dealer in electrical goods, together with all other materials necessary. Send for prices and particulars to Western Electrical Co., Bethune St., New York, N. Y. (546) (a) In the Scientific American Supplement," for October 8th, 1898, there is an article by A. Lieberknecht, in which a new building material called "Papyristite" is mentioned. Can you tell me anything about this material, and of what firm in the United States it can be obtained? (b) We know that the top of the wheel of a running buggy goes faster than the bottom. In the accompanying diagram, S represents the sun, and E the earth; may not the earth be considered as a planet wheel running around the circumference of another wheel I. and does not the point a on the earth travel faster than the point b? Granting that this is so, the dark side of the earth must always be traveling faster than the light side; in other words, the surface of the earth travels faster during the night than during the day. May not this account for some of the magnetic and electric disturbances? (547) (a) Kindly publish a table giving the life of the telegraph pole when set in sand, in gravel, in clay, and in loam; include the following woods : cedar, tamarack, black poplar, white poplar, Pinus Banksiana, and spruce. (b) Is the life of a pole increased, if the surface for 2 feet below the ground and 6 inches above is painted with the following mixture coal tar, pitch, and 1 pound of tallow added, all melted together in a pot and applied as hot as possible? (c) How many holes, 5 feet deep and 18 inches in diameter, ought one man to dig per day of 10 hours, in clay, in sand, in gravel, and in loam, using a spoon and digging bar? (d) What are the best pliers for telegraph work? H. G. H., N. W. T., Can. ANS. (a) The average life of poles under ordinary conditions may be placed as follows: Norway pine, 6 years; chestnut, 15 years; cypress, 12 years; cedar, 12 years; white oak, 6 years. The first four mentioned kinds of wood in this list are those most commonly used for telegraph and telephone poles in the United States. We have no data concerning the other woods you refer to, and it would be almost impossible to compile a reliable table giving the life of each under the various conditions you mention. The life of a pole depends more on the climatic conditions than on the kind of soil in which it is embedded, and therefore a table which might be approximately correct for one portion of the country would be entirely incorrect for another. The kind of soil in which the pole is set does not figure in the life of the pole to such an extent as might be at first expected, for decay always sets in at what is termed the "wind-and-water line," that is, just at the surface of the ground. This is due to the fact that the alternate action of the air and water upon wood is much more destructive than the constant action of either one or the other alone. (b) The life of the pole would undoubtedly be increased if coated as you mention. Another good method is to apply hot pitch to the end of the pole for a distance of 6 feet from the butt. (c) It has been found that in average soil a man can dig eight 5-foot holes in 1 day of 10 hours, using preferably a 7-foot spoon shovel and an 8-foot digging bar. Of course, this figure does not apply where dynamite is to be used for blasting the holes. (d) Stubb's side-cutting pliers are probably the best for all-round telegraph work. A very fine grade of pliers is manufactured by Mathias Kline & Son, 85 W. Van Buren street, Chicago, Ill. (549) (a) I have a small foot-power lathe, the headstock of which is fitted with a three-step cone pulley; the steps are 2 inches, 4 inches, and 6 inches in diameter. The largest step in the driving pulley is 28 inches in diameter. What should be the size of the other two steps on this pulley? (b) Do you know of any way in which a glass plate that is warped or bent can be straightened and made perfectly flat? C. J. S., Jamestown, N. J. ANS.-(a) You do not give the distance between centers nor the thickness of belt. Assuming these values as 30 inches and .2 inch, respectively, the two steps should be 254 inches and 271 inches, respectively. (b) Nothing but exposing the plate, resting on a flat surface in a furnace, to an even heat great enough to render it plastic will accomplish this. * * (550) I want to heat a one-story building by hot water; the interior of the building is a single room 10 ft. x 60 ft. I don't know how to connect the pipes to the heater so as to obtain a proper circulation of the water. Please explain by means of a small diagram. C. H. B., New Richmond, Ohio. ANS.-You do not tell us enough about your room, or your water heater, to enable us to give you any definite plan for running the pipes, or a sketch of the apparatus required. The following points, however, should help you: (1) Set your heater below the level of the radiators or coils with which you purpose to heat the room, and, if possible, locate it near the middle of the building. (2) Run a separate pipe direct from the top of the heater to feed each radiator with hot water. Pitch each pipe up towards its respective radiator, and arrange it so that air cannot collect and stop the circulation. (3) Run a separate pipe direct from each radiator, and connect it to the bottom of the boiler. This pipe is to convey water from the radiators back to the boiler, and must grade up towards the radiator to prevent air locks. (4) Place your radiators or coils against the outside walls and allow about 1 square foot of radiator surface for every 50 cubic feet of space in the room. (5) Place an air vent (a petcock will do) at the highest point of each radiator or coil, to let out air occasionally. (6) Attach an open expansion tank to the heater or to one of the pipes, care being taken to have no valve or stop-cock between the heater and this tank. The water-line in the tank should be at least 3 feet higher than the highest point of the highest radiator or any other part of the system. (7) Make your pipes equal in size to the radiator tappings; none should be smaller. (551) (a) Describe the most correct way of establishing a meridian. (b) Show how the azimuth of Polaris for any latitude is ascertained. (c) Give me the name of some book that is considered an authority on the above subject, and contains the azimuths calculated for the different latitudes for cach hour of the 24. C. M. G., Georgetown, Ohio. ANS. (a) There are several methods of establishing a meridian; such as by sun shadows, by equal altitudes of a star, by circumpolar stars, by Polaris, and by solar azimuth. The correctness of all three methods depends, to a great extent, upon the pains its shadow falls fairly well inside the edge of the paper. About an hour or two before noon, when the sun is at S, place a mark with a pencil at the extremity of the shadow cast by the rod, and from the base of the rod as a center, and with a radius equal to the length of the shadow, describe an arc of a circle as shown. When the sun begins to drop again in the afternoon, watch the shadow until it once more touches the circle. Mark it, and bisect the chord drawn between the two shadow points, and draw a line cb to the base of the rod from the center of the chord. This line is the astronomical meridian. If the center line is drawn parallel to the magnetic north and south, as indicated by a compass, the angle abc is the variation of the compass at the place of observation. (b) The azimuth of Polaris, for any latitude when at elongation, can be computed by using the following formula: the 24; such a table would be useless, since Polaris is visible only during the hours between sunset and sunrise. * ** (552) The other day I found in a technical paper some remarks about three American steam engines, viz. the Porter-Allen engine, the straight-line engine, by Mr. John Sweet, and the engine constructed and manufactured by the Lake Erie Engine Co. The engines were described without the aid of drawings, and in such a general manner that it was impossible for me to gain any useful information from the article. Can you publish drawings and an explanation of these engines? If this is asking too much, kindly tell me where I can obtain the information. E. M., Erfurt, Germany. ANS.-Lack of space prevents us from answering these questions. You will find the engines fully described in the catalogues of their makers. Write to the following firms, and ask them for a catalogue describing their engines: Southwark Foundry and Machine Co., Philadelphia, Pa.; Straight-Line Engine Co., Syracuse, N. Y.; Lake Erie Engineering Co., Buffalo, N. Y. (551) I am a subscriber to HOME STUDY MAGAZINE, and read with great interest the articles on surveying. I cannot understand quite all that is given upon the subject of the retracing of lines in the article entitled "A Question in Land Surveying," appearing in the September, 1898, number. In the second paragraph on page 354, it is stated that, Except in the north and west tiers of sections, a quarter-section corner would be relocated on the section line midway between the adjacent section corners." Now, suppose I am running north between sections 1 and 2, and there is no quarter-section post to be found on the line between those sections, where must I relocate the corner? Should I place it midway between the corner of sections 1, 2, 11, and 12 and the corner on the township line, or 40 chains of the original measure from the former corner? You will confer a great favor by explaining this point. T. H. A., Cathlamet, Wash. ANS.-As this quarter-section corner is on the line between two sections in the north tier of sections, it is one of the exceptions mentioned in the statement that you quote, and consequently, if the original corner is lost, it must be relocated in line between the section corners and at distances from them respectively proportional to the original distances as recorded; the corner will therefore be at a distance of 40 chains of the original measure from the eorner of sections 1, 2, 11, and 12. If you will consult the notes of the original survey (of which you should by all means have a copy), you will find that this corner was established at a distance of 40 chains from the corner of sections 1, 2, 11, and 12, on the line run north from that corner, and that, whatever amount the distance from that corner to the closing corner on the township line (or true corner, if the line was corrected back) overran or fell short of 80 chains, the excess or deficiency was all thrown into the portion of the line between the quarter-section corner and the closing corner, usually rendering this distance fractional, that is, more or less than 10 chains. Knowing that the original position of the corner is its only true position, and bearing in mind the manner in which it was established in its original position, it is not difficult to understand the proper method of restoring it by measurement from the adjacent section corners, when all local evidences of its original position have become obliterated; for the conditions of the original survey must be reproduced as closely as possible. The line should be run and measured continuously from the corner of sections 1, 2, 11, and 12 to the corner on the township line, setting a temporary stake on the measured line at 40 chains. After the entire line has been measured, this stake should be moved forward or back along the line, according as the new measurement overruns or falls short of the original measurement, to such position that the respective distances from the stake to the adjacent section corners will be exactly proportional to the corresponding recorded distances. For example, suppose that the distance from the corner of sections 1, 2, 11, and 12 to the closing corner on the township line is recorded as 80.40 chains, but is found to measure 84.42 chains. As the quarter-section corner was originally estab lished at a distance of 40 chains of the original measurement from the section corner, we have the proportion 80.40:84.42:: 40: x, ANS. (a) We know of no book on this special subject. We are told that either the London "Engineer" or "Engineering" is about to publish a series of articles on this subject, for which the paper has been collecting data for some time. We would advise you to watch these publications, which you will find on file in New York at the Cooper Institute, the Mercantile Library, the Astor Library, and at the rooms |