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introduced into the boiler. Too much soda is injurious; it will cause foaming and also affect the surface of the gauge glasses. Begin with pound of caustic soda daily, and increase until you get a good working proportion.

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(211) I am a practical student of plumbing. local examining board asks the following question : "What are the causes of capillary attraction in traps? Describe its operation." I cannot answer this with any satisfaction to myself. Can you help me out? J. MCA. A., Pittsburg, Pa. ANS.-The cause of capillary attraction in traps, or in anything else for that matter, may be referred to the mutual attraction of the liquid molecules for each other and the attraction between these molecules and

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solid bodies. We might go on here to describe capillary phenomena between different liquids and solids, but the one most important in this particular case is that which takes place by the introduction of some kinds of solid matter in a water-sealed trap in a plumbing system. Now, there are many different ways in which capillary attraction can affect traps, and perhaps the following is as good a representation as we can find, being simple and quite liable to occur in plumbing work. The above figure shows a common, every-day connection between a wash basin a and a 14-inch lead S trap b. A piece of worsted or cotton twine e has caught over the strainer bars at the basin outlet and the loose end hangs down into the waste pipe. Water flowing from the basin has worked the string through the trap, but cannot wash it down into the drainage system. This string acts like a small siphon tube, and siphons the water out of the trap until the seal is broken. The figure shows how the water runs off the end of the string, drop by drop, and it also shows how sewer gas can enter the building through the trap thus unsealed. The direction of the sewer gas is shown by the arrows. The force which lifts the water in the trap and discharges it over the outlet ridge, thus de

positing it in the waste pipe, is simply that due to the attraction between the liquid and the surfaces of the many fibers in the string, or, as it is commonly understood, capillary attraction, and the water is siphoned out of the trap because the tail end of the string is lower than the water in the trap.

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(212) What is action and the advantages of a compensating cylinder on pumping engines? F. H. B., Rouse, Cal. ANS.-In an ordinary direct-acting pumping engine the steam cannot be used expansively, since the pressure on the steam piston must be nearly constant in order to overcome the constant resistance of the pump plunger. If a flywheel is used, it will store up energy during the first part of the stroke to be given out during the latter part; this will permit the steam to be cut off at an economical point in the stroke, and at the same time furnish a nearly steady force to drive the pump plunger. Direct-acting pumps have some advantages over flywheel pumps for certain classes of work, and the compensating cylinder is used in order to do the work of the flywheel, and so make them more economical in their use of steam. During the first half of the stroke, when the pressure in the steam cylinder is the greatest, the compensating cylinder acts to compress the air in an air chamber, thus storing up a part of the energy developed by the steam; during the latter part of the stroke, after the steam has been cut off and the pressure acting on the steam piston reduced in consequence of its expansion, the air that has been compressed acts through the compensating piston to assist the steam.

(213) (a) Please give a good preparation for tempering soft steel; also a good process for annealing hard tool steel. (b) Where can I get a good treatise on gear cutting? G. T. K., Kings Mountain, N. C.

ANS. (a) The grade of steel generally known as soft steel cannot be hardened or tempered. To anneal tool steel, heat it red hot, then bury it in either slaked lime or wood ashes and allow it to cool. (b) We know of no book devoted to gear cutting. Write to the Brown & Sharpe Mfg. Co., Providence, R. I. They publish a book which includes much good advice on gear cutting. George B. Grant, Lexington, Mass., also writes much on gears and gear cutting; write him too.

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(214) (a) What is an inspirator, and how does it work when forcing or pumping water into a boiler? (b) What is the lowest pressure of steam it will work with? (c) Is it similar to, and what advantages has it over, an injector? (d) What is the pressure of the atmosphere per square inch, carried to seven decimal figures, and what is the height of a column of mercury equal to such pressure? (e) What is the derivation and pronunciation of the word adiabatic, which I am unable to find in Webster's Unabridged and two other dictionaries?

G., Northwest Territories.

ANS. (a) An inspirator works on exactly the same principles as an injector, the only difference being in the arrangement of the parts. The action of injectors and inspirators is explained in an article in HOME STUDY, September, 1896. (b) The pressure with which an inspirator will work depends on its construction. Injectors are made that use the exhaust steam from the engine to feed the boiler. (c) See answer to question (a). (d) The pressure of the atmosphere varies for different altitudes, temperatures, degrees of moisture, etc. At the level of the sea, and a temperature of 32° F., the pressure is approximately 14.69 pounds per square inch, this being a generally accepted average value, determined from a great number of different observations. The height of a column of

pressure is 29.92 from the Greek It is pronounced

mercury corresponding to this inches. (e) Adiabatic is derived a-dia-batos-not to be passed over. ad-ce-a-bat-ic, with a slight accent on the last syllable, and a heavier accent on the next to the last syllable, Adiabatic expansion means expansion without the transmission of heat to, or from the expanding body. If, for example, steam is allowed to expand, its temperature will fall; but. if the expansion is adiabatic, no heat will be given up to or taken from the walls of the vessel containing the steam; such expansion is never obtained in practice.

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(215) If a hole 2 feet in diameter is bored transversely through a 2-foot shaft, how many cubic inches of metal are removed? R. J. D., Canton, O. ANS.-Let O be point of intersection of the cylinders; cut the cylinders by a plane parallel to their axes; let OP be perpendicular to this plane, and let

(218) (a) What is the difference between hydraulic and Portland cement? (b) Which have the greater holding power, cut or wire nails? (c) What is the freezing point of glycerin? (d) Which is the better, black-or cream-colored fireclay? W. T. C., New Castle, Cal.

ANS.-(a) Portland cement is hydraulic cement, so-called because it has the property of setting in water. There are, however, two general classes of hydraulic cement, namely, Portland cement and natural cement; the latter is also called Rosendale, American, and Roman cement. All hydraulic cement consists, essentially, of lime and clay intimately mixed, thoroughly burned, and finely ground. The Portland cement is an artificial mixture, in such proportions as experience has shown to give the best results. Natural cement is made from the natural limestone. (See HOME STUDY, April, 1896, article entitled "Hydraulic Cements.") (b) Cut nails have considerably greater holding power than wire nails. (c) Pure glycerin solidifies at 40° C. to a gummy mass, which melts at 17° C. (d) The best fireclay consists of a mixture of 85 per cent. of Chinese kaolin and 15 per cent. of silica as quartz. The composition of kaolin is:

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(216) Why do some railroad-car wheels make a loud humming sound, while others do not? I notice that as a general rule it is the new trucks that make the noise. J. G. K., Forked Deer, Tenn. ANS.-The fact you mention has not come within our notice. When the wheels are new the flanges are of full contour, and there is therefore a certain amount of rubbing on the sides of the rails-more, at any rate, than will obtain when the flanges are worn. This, together with the fact that everything about a new truck is also more or less snug, may possibly account for the phenomenon.

(217) Please answer the following: A ship is about to be launched. (a) Please tell me under which of the three following conditions she would be most retarded and least retarded, after she enters the water: no propellers on; propellers fastened to shaft and allowed to turn freely; propellers fastened to shaft, but locked and not allowed to turn. (b) What is the cause of the pitting or corroding of the tips of propeller blades? (c) Are you prepared to answer general questions on naval architecture? H. P. W., Seattle, Wash. ANS. (a) We are not aware of any experiments having been made in this direction. At any rate, the retardation due to the propeller will be infinitesimal. (b) No satisfactory answer to this question has ever been given. (c) No; such questions entail far too much labor to be answered through the Answers to Inquiries columns of a magazine.

It can be colored black by adding to the mixture of kaolin and quartz some black lead.

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(219) (a) Will you give me information in regard to the best method of polishing ebony? (b) Also where I can procure a piece of ebony?

E. C., College Park, Md. ANS. (a) To polish ebony or other close-grained wood, wrap a piece of cotton cloth around a wad of plain cotton and saturate it with shellac varnish. Rub the previously sandpapered ebony surface with this cotton pad, lubricating it, if necessary, with a drop of raw linseed oil applied to the surface of the rubber. Let this surface dry for 24 hours and repeat the operation with a new rubber, previously sand papering, if necessary, to remove any unevenness. To finish the surface, moisten a clean cloth with a few drops of alcohol and rub briskly for a few minutes. (b) Ebony may be procured from Uptegrove & Co., East Tenth Street, New York City, or any of the leading piano manufacturers.

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(220) (a) How can latitude and longitude be determined by an observation on Polaris without waiting for culmination or elongation? (b) How can the azimuth of Polaris be determined for any hour? (c) Can a table be had showing the azimuth of Polaris for each day in latitudes north of 50°?

X. Y. Z., Cedar Rapids, Ia. ANS. (a) Polaris is not used for determining longitudes. To find latitude by an observation on Polaris, or any other star, at any time, note the time of observation; reduce it to sidereal time and then to degrees, remembering that 1 hour = 15 degrees; take star's right ascension from Nautical Almanac. Then, have angle of star = H (sidereal time) (right ascension). Measure altitude h of the star; correct it for refraction, (see HOME STUDY MAGAZINE, May, 1898, Answers to Inquiries, No. 158), and subtract result from 90°. Then, 90°-h== zenith distance. Take declination d from Nautical Almanac. Then, ifl is the latitude of the place, sin h = sin d sin + cos d cos l cos H. An easy method for solving this equation forl is given in the number of HOME STUDY just referred to. (b) The

cos / cos z

azimuth A for any latitude is given by the formula, sin (z+d) cos (z+ 1 + d). sin A = √ If is not known, it may be computed as explained above. (c) We do not happen to have a table of this kind at hand. Ordinary American books on surveying give azimuths of Polaris between latitudes 30° and 50° only, these being about the limits between which this country lies. European books give azimuths for higher latitudes, and the same are given, if we remember well, in some Reports of the U. S. Coast and Geodetic Survey.

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(222) I want a traction engine about 15 horsepower to do regular farm work, such as plowing, threshing wheat, hauling, etc. Can you tell me where and at what price I could get such an engine?

J. B., Fredericksburg, Va. ANS.-The following firms are builders of traction engines: Nichols & Shepard, Battle Creek, Mich.; J. I. Case Machine Co., Racine, Wis.; C. Aultman & Co., Canton, O.; Guar, Scott & Co., Richmond, Ind. The price may vary from $1,000 to $1,500.

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(224) Will you please inform me how to calculate the following: A boiler containing 3,000 pounds of water and 22 cubic feet of steam space has the furnace so banked that the pressure remains steadily at 65 pounds per square inch by the gauge; the throttle or stop-valve being opened for the space of one minute, the pressure is found to have fallen to 64 pounds per square inch. What has been the approximate evaporation during that time?

V. W. T., Cascade Locks, Ore. ANS.-The fall of pressure from 65 to 64 pounds per square inch causes a decrease of about 87° F. in the temperature of the water. (This may be found from steam tables.) The water gives up, therefore, 3,000 X

.872,610 British thermal units. At this pressure the latent heat of steam is about 895 B. T.U., that is, 895 B. T. U. are required to evaporate 1 pound of the water. Hence, the weight of water evaporated is 2,6108952.92 pounds, approximately. It is assumed that the heat given to the boiler by the banked fire is so small that it may be neglected.

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(225) (a) Kindly furnish a rule for the proportioning of cylinder flanges and bolts such as I illustrate in Fig. 1. (b) Also furnish a rule for the proportioning of pulley hubs. (c) Will this last rule do for flywheel hubs too? H. C., Brooklyn, B., N. Y. ANS.-(a) If p is the pressure in the cylinder in pounds per square inch, and D the diameter of the cylinder in inches, the dimensions of the flange and bolts may be made as follows: thickness of

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radius of the pulley, and d the diameter of the shaft, the diameter D of the hub may be made equal to d + (B+ R) +inch. The length L of the hub may be made equal to B. (c) The proportions of the hub of a flywheel depend on the weight of the wheel and the variations in its speed. A rough rule for the hub of a flywheel is to make the diameter D of the hub twice the diameter d of the shaft, and the length L of the hub 1 times the diameter d of the shaft; i. e., D 2 d, and L = 1 d.

(226) I wish to float a substance in a liquid-the liquid to be as cheap as possible, but not an acid nor very poisonous to handle. The specific gravity of the substance is 1.33. Of course the chemical must dissolve in water, and have a specific gravity of from 1.36 to 1.40. L. A. O. G., Brookwood, Ala. ANS.-A solution of "soluble glass" (sodium silicate) will answer the purpose.

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(227) Will you please explain the advantage, if any, in making the vanes of a windmill of a curved section? There are windmills here with the concave surface of the vanes towards the wind, and others with the convex surface towards the wind. I suppose if one is right the other must be wrong. I may say that I have examined the wheels and they are put together as they were intended to be by the makers. No mistake has been made in the erection.

F. D.. Johannesburg, South Africa.

ANS.-We see no good reason for the use of curved vanes. A flat vane, twisted so as to conform approximately to the form of a true helix or screw, will give excellent results. In choosing between vanes with convex or concave surfaces to the wind, the latter will undoubtedly give the best results. The curved vane is the outcome of a fancied analogy between the windmill and the screw propeller, while, in fact, there is considerable difference in the operation of the two. An article on windmill construction will be found in the March, 1898, number of HOME STUDY MAGAZINE.

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(228) (a) Can you give me an idea what the area of the inlet and exhaust ports of a gas engine should be, constructed on the principle of the Day type, as described in HOME STUDY MAGAZINE February, 1898? Take, for example, an engine having a 34-inch cylinder and a 34-inch stroke, and give the sizes of the ports. (b) Is there any rule for calculating the size of these ports with reference to the diameter of the cylinder and the length of stroke? (c) In the Day engine I take it that the lower edge of the exhaust port is horizontally opposite the top edge of the inlet port. Am I right? (d) Would the gas-engine card published in the February, 1898, number in answer to question 8 be an average card for an engine of the Day type?

G. H. J., Sparrow's Point, Md.

ANS. (a) Make the area of the inlet port 14 square inches, and that of the exhaust port 19 square inches. (b) A good general rule is to make the area of the inlet port 12%, and that of the exhaust port 16, of the piston area. (c) See answer to question 117 in HOME STUDY MAGAZINE for April, 1898. (d) A card from the Day engine would be very similar to the one referred to.

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(229) The following is an extract from a newspaper article describing an explosion in a brewery: "By the bursting of a compressed-air pipe in the icemachine room of George Ringler & Co.'s brewery, at 213 East Ninety-First Street yesterday, Chief Engineer Carl Hoening, 51 years old, of 315 East Ninety-Third Street, was killed, and Adolph Schenken, 23 years old, of 231 East Eighty-Eighth Street, received several severe wounds, and is at the Presbyterian Hospital. The pipe, which is 12 inches in diameter, about an inch thick, and 14 feet in height, connects the ammonia tank with one of the engines. A numher of heavy-pressure tests had been made, and Hoening was submitting the pipe to a greater test when it exploded. A shower of heavy pieces of metal fell in all directions. Two large pieces struck Hoening squarely on the top of his head crushing in his skull. By almost a miracle John Hoening, the son of the dead man, escaped injury. He was standing by his father watching the test and assisting him. Every window in the room was shattered, and the pipes, large and small, with which the roof and walls are lined, were snapped as though they were pieces of clay. The machinery in the room was torn and broken in many places, and in some

instances flying iron missles went through sheet iron as if it had been pine board." (a) Is it not probable that this explosion was caused by oil in the pipes? Will you kindly explain how these explosions occur in refrigerating machinery? (b) I have noticed in New York a number of gas engines fitted with a rubber bag, which is usually connected just over the engine. Will you kindly explain its use and state how far the bag should be from the exhaust pipe of engine to prevent all danger of an explosion? E. S. A., Brooklyn, N. Y. ANS.-(a) The explosion may be due to either of two causes: First, carelessness in testing, and rupture due to excessive pressure; the article reading, "and Hoening was submitting the pipe to a greater test when it exploded." Second, an explosive mixture composed of hydrocarbons, liberated by the heat of compression from the lubricating oil, and the oxygen of the air. The oil used for lubricating icemachine cylinders is a mineral oil, having a low, cold test, but not a very high fire test. This oil gives off various hydrocarbon gases at comparatively low temperatures. These are highly explosive when mixed with air. If insufficient jacket water is circulated, or if the compressor is of the Linde or wetcompression type, care must be exercised by running slow, not to develop a temperature high enough to explode the mixture. The flame of a lamp is sometimes used to detect a leak; this is liable to ignite this mixture. (b) The purpose of the gas bag is fully explained on page 9 of HOME STUDY MAGAZINE, February, 1898. There are two conditions under which an explosion can occur in this bag. One condition is the presence of sufficient air mixed with the gas in the bag to produce an explosive mixture; the other, expansion of the gas in the bag, due to confining the gas without opportunity of escape, and rise of temperature. An explosion in the first instance would require the ignition of the mixture; in the second, exposure to unusual heat. The formation of an explosive mixture in the bag may be said to be exceedingly improbable. The overheating of the bag from the exhaust pipe can be avoided by placing the bag 2 feet or more from the exhaust pipe.

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(230) Can you tell me (a) how to polish horn? (b) how to remove ink stains? J. B., Fredericksburg, Pa. ANS. (a) Various methods are in use. A felt polishing wheel can be employed, using finely-ground pumice with water, finishing off with rottenstone. Or you can scrape the parts quite smooth, and then rub down with very fine sandpaper, followed by powdered charcoal and water, applied on a bit of felt. Then use rottenstone or putty powder and polish finally with chamois leather dampened with sweet oil. Or you can finish off by rubbing in subnitrate of bismuth with the bare hand. (b) If the stains are in the hands, use lemon juice. If in clothes or in other fabrics, lemon juice will sometimes prove effective. If not, try a solution of oxalic acid (1 part acid to 2 parts water). Rub in well with a soft rag. A very good remedy is pyrophosphate of soda, which does not injure the fiber of the cloth. First put a little tallow in the ink stain and then wash in a solution of the above soda, until both ink and tallow have disappeared.

(231) Please inform me whether there are any objections to the use of piston igniters in gas or gasoline engines; and if so, what they are?

A. R. R., Winona, Minn. ANS.-We do not know what you mean by a “piston" igniter. There are several igniters to which this name might be applied.

(232) I enclose a sketch of a fan. (a) Please give the proper proportions to get the largest volume of air through it, and have a keen, stiff blast through the delivery pipe. (b) If the angle of delivery pipe is changed to 400, and the radius of curve is changed from 3 feet to 2 feet, will the capacity of the fan be increased or decreased, length of the pipe remaining the same, 12 feet? C. W. Q., Bloomington, Ill.

ANS.-(a) Assuming that by a "keen, stiff blast" you mean a velocity of air through the delivery pipe of about 150 feet per second, the dimensions of the fan for your pipe should be about as given in the figure.

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You will notice that the outer circumference of the casing, instead of being concentric with the fan shaft, is spiral-shaped, so as to gradually increase the area of the passage for the air toward the outlet into the delivery pipe. (b) It is probable the capacity would be decreased.

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(233) (a) Will you please explain the following strange behavior of an electric bell: There are times when, though I make the proper connection, the bell will not operate, no current passing through the wires for the time being; but the instant I press the hammer against the gong the current flows and the bell rings. It is an ordinary electric door-bell and is used for signaling purposes. Please explain the operation of the bell in detail. (b) What is the breaking strength of a 4-inch six-strand (7 wires to the strand) crucible-steel wire rope; and what is the safe working strength?

G. W., Sand Coulee, Montana. ANS. (a) The adjustable screw, bearing on the spring of the armature, is not properly set. A detailed explanation of an electric alarm bell may be found on page 25 of the August, 1897, number of HOME STUDY FOR ELECTRICAL WORKERS. (b) For the best grade of crucible-steel wire, known as " plough-steel" wire, the breaking strength is about 66,000 pounds, and the safe working strength 13,000 pounds.

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(234) (a) Supposing I want to cut a bastard thread, say 8 threads to the inch, and having the sides of the thread cut to an angle of 7°, what width would I have to make the point of the tool, in order to cut the proper depth and have the top and bottom of the thread exactly the same? (b) Suppose I have a piece of stock 54 inches long which I wish to turn to a taper inch to the foot, how far over would I want to set the dead center of my lathe?

F. H. F., Springfield, Mass.

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(236) Will you kindly tell me if there are any books published on the designing of machinery for refining beet and cane sugar. or either; also, the address of parties I can get such machines from?

W. O. D., Cold Spring, N. Y.

ANS.-We do not know of any book treating upon this subject. Most of the machinery used in sugar refining is made in Germany. Write (in English) to Zimmerman & Son, Halle an der Saale, Germany, or to Gruson's Maschienen Werke, Magdeburg, Germany, who will furnish you with all the information concerning price, etc. you desire.

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(237) (a) I am running a T. H. arc machine-25 lamps. It is necessary, in order to feel the bearing nearest the leather belt, to approach my elbow within 3 or 4 inches of the pulley rim, and the static charge to my elbow is then so severe that I hate to touch the bearing. The machine is so arranged that there is no other way of getting at the bearing. How can I conduct the discharge away? (b) Would a board covered with tin and driven full of nails, placed within 3 inches of the belt bottom-the wire being led to earth-be of any use? (c) An arc machine and an incandescent machine are within 4 feet of each other and are running nicely. Are they dangerously close together? They get their motion from the same engine; their belts are 12 inches apart, as in sketch enclosed. (d) Can you recommend or send to me a good book on the diseases of arc machines and are lamps, with their remedies? (e) I wish to charge 4 storage cells from the dynamo that is running lights after 9 P. M. Most of the load is off the machine and I wish to charge storage cells while running the other lamps. Please explain by means of a diagram how I can do this.

C. J. S., Oakland, Cal. ANS.-(a) The frame of the machine may be grounded, but this is not advisable, although it is recommended by some station managers. In your second question, you have suggested a far safer and more reliable means of obtaining the same result. (b) Yes; this will work well if the wire has a good ground. The sharp points increase the efficiency of the apparatus. Another way would be to connect the machine frame to the earth through a heavy pencil mark on a piece of hard, dry wood. The static charge would thus be enabled to escape to the earth, and the insulation would not be subjected to any increased electrical stress. (c) Electrically, no: provided the machines are on insulating bases, and are located in a dry place. The belts may be considered dangerously close, because, if one belt is thrown off by an overload, it may become entangled with the other, and possibly wreck the dynamo, and the engine also. Such a catastrope can be averted by erecting belt guards. (d) You can get more information from trade catalogues than from books, on the construction of arc lamps. You can, however, obtain more satisfaction from the lamp itself, if you devote two hours to taking it to pieces, putting it together, tracing the circuits, following the mechanical motions, observing the magnetic effects, etc.,

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