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Hints to Correspondents Names and Address must accompany ' all letters, or no attention will be paid thereto. This is for our information aid not for publication. References to former articles or answers' should give date of paper and page or number of question Inquiries not answered in reasonable time should be repeated; correspondents will bear in mind that some answers require not a little research, and, though we endeavor to reply to all either by letter or in this department, each must take his turn. Special Written Information on matters of personal rather than general interest cannot be expected without remuneration. Scientific American Supplements referred to may be had at the office. Price 10 cents each. Books referred to promptly supplied on receipt of price. Minerals sent for examination should be distinctly marked or labeled. (4787) G. W. V. asks how to make a La- lande oxide of copper battery in the cheapest way possible. I heard that they could be made of tin tomato cans. A. See SUPPLEMENT 792. (4788) F. T. G. asks: If one heat unit raises the temperate of one pound of water one degree, how many heat units will be required to raise the temperature of one cunic foot of air one degree - A. One heat unit will raise one pound of air one degree. One pound of air at sixty degrees is equal to thirteen cubic feet. Then one-thirteenth of a heat unit will heat one cubic foot of air one degree. (4789) F. W. Q. asks whether he can get the same amount of electricity from a battery by immersing the zinc half way into the solution instead of all the way; as, for instance, in the Grenetbattery described in SCIENTIFIC AMERICAN SUPPLEMENT, No. 157. A. By immersing the zinc one half way into the solution, you will get less current than you will if it is entirely submerged; the electro-motive force, however, will be the same in both cases. (4790) A. P. J. asks what wash or prevention, if any, may be used to arrestpowder posting in a chestuut bookcase. Fine powder issuing from small holes in the shelves is a constant annoyance. Reply by Prof. C. V. Riley.--Without having seen specimens Df the author of the injury described by your correspondent, it is impossible to definitely determine the insect which is injuring his chestnut bookcase. There are several coleopterous insects of the family Ptinidre which are notorious as infesting the wood used in the manufacture of desks, 1893 SCIENTIFIC AMERICAN, INC. 204 Ithutiiu jmmtfttt. [APRIL S8 1893. household fumiture, the handles of varions implements, etc., and these are known as powder post beetles. Some of these belong to the genus Lyctus, of which L. striatu lus is known to do similar injury to that described. These beetles are, however, more often found working outdoors, and the damage may be done by another common Ptinid beetle, the Sitodrepa panicea, which more often affects woods indoors and made into cabinets. The presence of these insects is always indicated by small circular holes, through which the beetles have entered the wood, or by small heaps of the dust which is pushed out by the burrowing larval. The beetles are small, of a brownish color, and their larval are small, six-legged, somewhat hairy, yellowish-white grubs, with their bodies more or less curved toward the extremity. Wood once thoroughly infested by the beetles or laval is beyond redemption; but in the case of the beginning of the injury, or as a preventive, washing, and if possible soaking, the wood in kerosene will act as a preventive and also destroy the beetles and larval as far as the oil penetrates. Where the wood is of such a nature that it can be submitted to stove or kiln heat without damage, it may be thus disinfected. (4791) C. G. writes: I notice in SCIENTIFIC AMERICAN of March 4 a cut of a storage'battery. Do I understand you as meaning that there are no zinc plates used at all - Is it simply sheet lead plates coated with red lead - Do I use same connections to charge battery as discharge it - Must the cell be air tight - How shall I know when it is charged - What book can I get to give me good knowledge on storage system complete - A. There are several different types of storage batteries. In many of the types both plates are formed of lead; no zinc is used, and the lead plates are coated with red lead. The same connections are used forcharging and discharging the battery. The cell should not be air tight, as gases or vapors are generated which require a way of escape. For information on charging and using batteries, etc., we refer you to Salamon's Electric Light Installations, price 2. (4792) G. A. R. asks: What is meant by ampere hour, so often referred toin battery circulars - Does it mean that the capacity is say (in a 50 ampere hour cell) 50 amperes for 1 hour, 1 ampere for 50 hours, or 10 amperes for 5 hours, etc.- Where can I obtain directions for making gas out of coal on a small scale, and the purifying of the same, storage, tanks, etc.- What power would a 6 foot windmill of the air motor pattern develop - A. One ampere hour is 1 ampere of current flowing for 1 hour, one-half an ampere ot current flowing for 2 hours, one-tenth of an ampere flowing for 10 hours. On the other hand, 10 ampere hours may be 1 ampere for 10 hours or 10 amperes for 1 hour. We think of no small work on the manufacture of gas. We can refer you io Gas Works : their Arrangement, Construction, Plant, and Machinery, by F. Colyer, price by mail, 8. The windmill to which you refer will probably average about one-half horse power. (4793) O. J. asks: 1. In making fluid for bichromate batteries, do you add the sulphuric acid to water the first thing and then the bichromate potassium or bichromate potash to water and then sulphuric acid - A. The correct way to make thebichromate solution is to dissolve the bichromate first and afterward slowly add the sulphuric acid. 2. A recipe for a good luminous paint. A. For information on luminous paint, we refer you to SUPPLEMENT 497. 3. Is there any action on the zinc in a bichromate potash battery when the circuit is open - A. In the Fuller and Bunsen batteries there is scarcely any action on the zinc when the battery is not in use; bu 'n plunging batteries the zinc, if left in the solution, is soon destroyed. (4794) A. B. writes: I built the dynamo shown in SUPPLEMENT 60. Used it about three weeks on an arc light, when it burned out. Tried resistance in circuit, but it heated just the same and dimmed the light. Do arc light machines heat more than incandescent machines - Have a pair of fi eld maguets like those shown in SUPPLEMENT 60. Can't I make a two horse power ' machine by making the following changes - Place a piece of iron one-half inch thick between the polar yokes (where the pole pieces are bolted together) and face off the bottom of the poles, and add an inch thickness to each one, and then bore out to about 4 inches, taking care to throw the hole as much down as possible. The object of the pieces is to save stock. I would then wind ten layers of No. 16 wire on each pole in five pieces, each piece forming two layers, and add a shunt of fine wire on the outside, making a compound winding. Am sure the field could be made strong enough this way, even for a three horse power machine. What size wire should I use on armature say for about 60 volts - and how m(lny coils ought there to be - Would there be any advantage in makiug the rings with four holes on the sides for ventilation- A. In regard to your arc light, we would suggest that you adjust the lamp so as to give a longer arc, thus increasing the resistance of the circuit. If this does not prevent the overheating of the armature, add 15 or 20 ohms resistance to the circuit and ran the dynamo at a little higher speed. There is no reason why an arc light machine should heat more than an incandescent one if it is constructed for arc lighting. You could arrange your field magnet for a larger armature in the manner proposed. We cannot, without considerable calculation, furnish you the information you desire for the winding of your new armature. Probably your readiest way of getting at the matter is to see a machine of about the size desired and get your measurements from that. There will be an advantage in making ventilating holes in the armature, providing you do not cut out too much metal. (4795) F. B. asks whether England or the United States produces the largest amount of steel now. A. The United States now produce the largest amount of steel, to wit, for 1890, 3,50,00 tons, Great Britain 3,250,00 tons. (4796) H. A. asks: 1. What are the rules for finding the pitch of a'propeller wheel- A. The pitch is obtained by multiplying the circumference in feet or inches by the cotangent of the angle of the blade with the center line. Or take the angle by opening a folding rule on the edge of the blade and in line with the shaft aft. Lay off two lines at right angles and place the angle of the rnle on one line at a distance of the circumference of the wheel from the line representing the center of the shaft and extend the line represented by the opening of the rule to meet the cenai line. This forms a right angled triangle, of which the shaft line is the pitch in the same manner (feet or inches) that the circumference was taken in. 2. Does it require more power to ran a boat at a certain rate of speed with a small propeller wheel than with a larger one - A. Yes. Propeller wheels should be as large as possible to ran in solid water for economy. 3. How much pitch should a propeller have which is 14 inches in diameter, and how many revolutions should it make a minute to give a speed of 6 miles an hour to a shell boat, 16 feet long, with a very sharp bow, the boat weighing pounds- A. A14inch screw for a boat with fine lines should have 30 inch pitch and make 275 revolntions per minute for 6 miles per hour, allowing 20 per cent slip. 4. When the pressure in a boiler is up at a certain point, say 70 pounds, does it require more fuel to keep it there than at a lower point of pressure - A. The amount of fuel required to lIeep the steam at a specified pressure depends entirely upon the power used. It takes more fuel for a given power at the lower pressure. (4797) J. G. C. says: Will you please give a recipe for a paste that T can use on the face of a photograph, so I can mount the print face down on glass, something that will not discolor the face of the print and is not costly - A. To mount prints on glass follow the directions given by J. E. Dumont; that is, take 4 ounces gelatine and soak half an hour in cold water, then place in a glass jar, adding 16 ounces of water; put the jar in a large dish of warm water and dissolve the gelatine. When dissolved pour into a shallow tray. Have your prints rolled on a roller, albumen side out; take the print by the corners and pass rapidly through the gelatine, taking great care to avoid air bubbles. Hang up with clips to dry; when dry, squeeze carefully on to the glass. The better the quality of glass the finer the effect. From The Scientific Ameriean Cylopedia of Receipts, Notes and Queries." (4798) A. S. writes: I would like to make a steam whistie, 12 inches diameter. What would be the proper length and what would the proportions be for a whistle one octave higher in tone than the 12 inch - A. A 12 inch whistle is usually made from 20 to 24 inches high. For an octave make the whistle about oue-half the volume, subject to corrections for thickness of metal. (4799) B.&T. ask: What will take off lampblack that is used in mortar and has got on the face of the brick - Our mason used muriatic acid and then put on linseed oil. What will clean it, if anything - A. Rub with a piece of pumice stone or sandpaper. (4800) F. M. W. and others ask for a ce- mentfor use in making aquariums. A. Litharge, fine, white, dry sand, and plaster of Paris, each 1 gill; finely pQ,lverized resin, gill. Mix thoroughly and make into a paste with boiled linseed oil to which drier been added. Beat it well, and let it stand four or five hours before using it. After it has stood for fifteen hours, however, it loses its strength. Glass cemented into its frame with this cement is good for either salt or fresh water. It has n used at the Zoological Gardens, London, with great success. It might be useful for constrncting tanks for other purposes or for stopping leaks. Ortake linseed oil, 3 ounces; tar, 4 ounces; resin, 1 pound; melt together over a gentle fire. If too much oil is used, the cement will rn down the angles of the aquarium. To obviate this it should be tested before using by allowing a small quantity to cool under water. If not found snffici- ently firm, allow it to simmer longer or add more tar and resin. The cement should be poured in the corners of the aquarium while warm (not hot). This cement is pliable, and is not poisonous. Paraffine applied to the bottom, if it is of wood, will make it waterproof. Have the wood dry and very hot; rab the paraffine in thoroughly. (4801) B. W. P. says: Will you inform me whether any kind of grapes may be used to make raisins - A. No. The Muscatel is the principal grape grown to make the raisin, and its flavor excels that of all other varieties. For many years Malaga, Spain, has produced the best frait, and previous to the introduction of Muscatel cuttings into California, our supplies were brought from port. There is a difference of opinion in regard to the quality of the frait produced in Malaga and California, the people in the far West claiming the latter to be superior; but unbiased experts consider the former superior in flavor, richer in sngar, more tender, and larger fmIt. (4802) H. N. says : I want to know what will be the pressure per square inch when air is compressed to one-half its natural bulk or size. Also what the pressure when pressed to one-frd of its natural bulk. Would there be any.difference if the quantity were large or small - A. For ordinary practical purposes, if the air is to be measured at a uniform temperature (isothermal compression), and calling the atmospheric pressure equal to 15 pounds the formula, pressure X volumes -- pressure the pressure of compression. Taking your inquiry, 15 X 2 30 -- 15 15]lounds pressure and 15 X 3 45 -- 15 30 pounds pressure. This will not be the pressure at the instant of compression, because the heat generated by compression expands the air, and at the moment of leaving the cylinder it may have a pressure of 20 pounds in the first Case and 50 pounds in the latter. With water-jacketed cylinders, much of the heat of compression is absorbed and the final pressure drops nearer to the isothermal line. See SCIENTIFIC AMERICAN SUPPLEMENT, No. 799, on air compression. (4803) N. G. writes : About twelve miles from here is a very large spring. I think it must be about one thousand feet higher than this place. A mountain (or hill) higher than the level of the spring lies between us. Which do vou think would be the best and cheapest means of conveying water to this city--by siphoning it from that spring, over the hill to a reservoir here, or by pumping it with steam from a river that rans through this place to a reservoir about one mile distant- Also please tell me where would be the bestplace to send my son to get a thorough knowledge of machinery, both steam and electric. A. If the flow from the spring is large enough for your city supply, it will be the best and cheapest water supply, considering the expense of pumping. A siphon of 10 or 15 feet lift might be made available, but will have to beoften relieved of accumulating air. For siphon, any height above 15 feet could not be made practicable in so long a line of pipe. You do not give detalls enough for the best advice. It is worth your while to have a survey made as to the whole grade and ascertain whether a detour could be made for a gravity flow. If the water in the river is good, a large ram with a fall of 4 or 5 feet would make an economical water supply. Steam is a constant expense. Perhaps windmills could be used. The Rose Polytechnic Institute, Terre Haute, Ind., is one of the best schools in mechanical and electric engineering in the West, also the Vanderbilt University, Nashville, Tenn. (4804) J. E. S. writes: 1. I have a well 140 feet to water, which is inexhaustible. By going 40 feet deeper we fi nd dry sand, whichabsorbs all the water unless plugged below the water line, or we stop drilling before we get through a very rock that lies directly on top of the dry sand bed. Can I raise the water with a hydraulic ram - Give instructions for putting in. If not, is there an automatic apparatus that will raise the water- A. You cannot raise water from bored well with a ram, unless by enlarging it, you can sink a pipe through to the absorbing stratum below, to .carry off the water used to work the ram and create the necessary pressure. There are oil and gasoline engines and air engines used for pumping water from wells. They all require care. A windmill will) be the best automatic machine. 2. Does the moon revolve ou an axis as the earth does- If so, why is it the same spots face us all the time - A. The moon makes one revolution on her axis in the same time that she makes one revolution around the earth, and that is the reason why the same parts face us all the time. 3. What shades the moon or causes its 5erent phases - A. It is the reflection of the sun's light on the moon that makes her appear to vary in form. 4. How near has any of the heavenly bodies ever been to the earth, and what is the nearest to the earth at present - A. The moon is the nearest heavenly body. She is 240,00 miles distant from the earth. 5. What body or bodies will cause the eclipse of the sun April 16 and October 9, and their distance from the earth - A. The moon coming between the sun and the earth produces an eclipse of the sun. (4805) C. M. H. says: I have a steam vacuum irrigating pump which draws water through an 8 inch pipe from a river 18 feet below. My supply pipe now runs diagonally from the pump into the stream, and as the pump is set some distance back from the edge, the supply pipe is necessarily 54 feet long. Will the lift of the water be less if I cut a ditch from the river to a point directly underneath the pump and run my pipe vertically down- If so,how much less will be the weight of the water- A. The weight of the water in the suction pipe is due to its vertical height only. There will be no difference in the pull of the pump due to the two positions alone. The vertical pipe will have- less friction than the inclined pipe, as w II as less volume, and will require less poweI to overcome its inertia at the change of stroke in the pump, unless the vacuum pump is of a kind that will keep the water in the long suction pipe under a constant and equal velocity. As this is doubtful, and the possibility that the friction may add a foot, more or less, to the suction head, we advise the open ditch and vertical : suction. (4806) E. J. A. writes: We have a biHltl- ing 16 feetsquare, 16 feet posts, tight. We wish to place steam pipes in this for the purpose of drying slack barrel heading. We would ask: Our boiler is 25 horse power. Engine uses (develops) but 5 or 8 horse power. Will that not leave boiler steaming capacity to make plenty of steam for this size kiln - We have excellent fuel. Boiler and engine are about 60 feet from kiln building. Will we lose much heat, piping this distance, if we lay pipe in ground, usinb asbestos packing- What size pipe, to use live steam, would we need, and how many feet, in building, to develop all the heat possible, as there is not much danger heating the material too fast or too much, so as you don't bum it up- Do you think it practical to use steam for drying- We want to develop 150 or 160 of heat in kiln if we can. Boiler,pressure 30 pounds. A. You can make a good drying room with the spare steam that you have, without waste of heat. The steam pipe should be thickly felted and the line underground laid in a box 8 inches clear inside, with 1 inch pipe well felted and supported in the center. Pipe in the room should be in flat coils under a lattice floor, 2,00 feet of 1 inch pipe, laid in sections so that it will clear- itself of water. The heading should be piled in racks above the floor. The condensed steam should be led back, through a pipe in the box and returned to the boiler. (4807) W. T. P. writes: I would like information how to build a breast or current water wheel and to gear same to centrifugal pump. I want to raise anywhere from twelve hundred to twenty-four hundred gallons per minute of time fifteen feet high for irrigation purposes. I want to know the length of wheel and diameter and how to gear wheel so it would adjust itself to and fall in river and how to prevent drift from injuring wheel in river. I have abundance of water inriver to get the power, if I could get some way to utilize the power in the river. A. You will require a wheel of about 15 horse power. You will fi nd the wheel that you describe illustrated and described in SCIENTIFIC AMERICAN, January 21, 1893,10 cents mailed. This form of wheel will have to be constructed to suit the velocity of current or the height of the breast. A millwright or clever carpenter should be able to build a wheel to suit the power required. (4808) L. W. S. asks: 1. When does the patent on the Bell telephone receiver expire- A. The patent)on the Bell telephone receiver expires in January, 1894. 2. In making one of the above telephones, would No. 38,wire be better than 36, when the telephoneis to be used on a line two or three miles in length - A. No. 38 would be better for use than No. 36, but it is more difficult to wind. 3. Is it the resistance in the line wire that causes telephones to fail on long distances - A. The failure of the telephone on long distances is due to leakages more than to resistance. (4809) H. V. F. asks: 1. Does the tele- phon, described in SCIENTIFIC AMERICAN SUPPLEMENT, No. 142, need any battery - A. No. 2. Will the telephone work on a line 450 feet long - A. Yes. 3. What size of copper te should I use - A. No. 18 will answer for the distance given. 4. Will the above suffice if I use the telephone call in Fig. 5 on page 2571 in SCIENTIFIC AFRICAN SUPPLEMENT,' No. 162 - A. Yes. 5. Shall I use rem ra or rem through the earth f A. Eitherretro will answer. (4810) M. J. B. asks the size of stack that should be put on kiln, size of which is 62 feet by 27 feet.by 7 feet, and containing 5,00 feet of steam pipe. We would like to remove the air out of the room about every ten minutes. A. Assuming the steam pipes are on ornear the floor and the lumber piled above the pipes, the ventilation in so large a floor space should be divided so as to make an even flow of air throughout the room. For this purpose at least six uptakes should be made through the ceiling, 18 inches square, equally dividing the areas of the ceiling. These uptakes need be no more than 8 or 10 feet high, with hoods to keep out rain, and dampers, so that they may be closed when steam is first turned on. (4811) A. F. writes: Are the numbers by which the different sizes' of electriclwiresarecalled arbitrary numbers or do they refer to measures, frac- ilons of inches, etc.- Suppose that for:making a telephone you saythat No. 18 wire is used, how can I convert that number in millimeters, as the diameter of wires is given in that measure - A. The numbers of the American wire gauge are arbitrary. For this reason you will have to get the sizes in mills or circular mills from some of the existing tables. You will find such a table in Sloane's Arithmetic of Electricity, price by mail 1. (4812) N. H. E. asks the cheapest and best way to color brass black. A. Dip the clean brass in a solution of chloride of platinum. (4813) W. B. R. asks how lead pipes are joined together by the use of a blow pipe. A. For soldering lead pipes with a blow pipe, a jump joint is made by opening one end bell mouth and scarfing the other end to fit in, when, by powdering the joint with resin and placing a pieceof strip solder around the joint, it can be heated by a blow pipe until the solder runs in and makes the joint. (4814) W. E. H. writes : Please give the process for etching brass signs. Also the japan or black material used to fill in with. A. The brass sign is painted all around the letters with asphalt vish and a wall of putty or soft asphalt raised outside the lettering to keep the acid from flowing away. Use nitric acid 1 part, water 2"parts, mix and pour on the plate to a depth of Y.i;inch. When bitten deep enough, wash dry and fill with melted asphalt or black sealing wax. (4815) C. C. M. asks : Can you give us any information about the use of aluminum for shoeing race horses- We have tried it, but find the metal too soft. Is there any way to harden it - A. As we assume that your o'Dject is to make a light shoe, we recommend an alloy of from 3 to 5 per cent of copper to aluminum. This will make the aluminum slightly heavier, but harder and tougher. Probably the 3 per cent alloy will be all that is required. (4816) T. T. asks: In firing a cannon, at what point will its projectile attain its greatest velocity - Also, how is the velocity of projectiles measured - A. The velocity of a shot is greatest at the muzzle of the gun. (4817) J. G. W. writes : I am making a quantity of very light castings with a core inside. The castings want to be very soft, so as to drill and tap easily. No strength is required. I find that while I have the iron soft enough on the outside, the core seems to chill the iron somewhat on the inside, thus making it hard on the tap. The core is made of boiled oil, resin, and moulding sand in certain proportions. What I want to know is this: Is there any formula for making cores that has a softening effect at the junction of the iron with the core - A. For cores try new mouldings, and mixed with as little paste as will allow the sand to hold together, and bake thoroughly dry in an oven. (4818) M. B. writes : I have to arrange a calendar for 1894, but have no tables from which I can find the time for the rising and setting of the moon for every day and in different places. Can yon give me some information regarding such tables - A. The Nautical Almanac gives the moon's position for every day in the year, with the necessary formulas. It is published by the government at Washington. (4819) F. B. says: I want a receipt for a paint to apply to a copper-lined bath tub from which the tin has been wom in patches. I would prefer some white color. A. Use ordinary white paint. (48W) J. H. H. asks : 1. How can I mix bronze powder in a liquid form - With what can I cut it- A. Mix the bronze powder in thin mastic varnish. 2. What size and how many blades should a propeller wheel be to propel a 13 foot canoe- A. A two-blade screw 10 inches diameter for the canoe. (4821) J. C. R. writes: I am building a small non-condensing compound marine engine of the following dimensions: Diameter of cylinders,H. P. in., L. P. 1:>8 in., stroke X in., size of ports H. P. cylinder 1-16X3-16, exhaust 3-32X3-16, L. P. cylinder 1-16X9-32, exhaust 3-32X9-32. Are the cylinders and ports in the proper proportion - If not, give size of L. P. cylinder. If the cranks are fixed at right angles to each other, give relative position of eccentrics to cranks. A. The cylinders are a good proportion, as are also the ports. The longer diameter of the eccentrics should be slightly ahead of a line at right angles to the crank. See Model Engine Making, by Pocock, 1 mailed. (4822) J. H. R. writes : I wish to layout my yard in walks. I do not care for brick, but a preparation to put on the gronnd. Now is there any cement oripreparation similar to cement that will stand freezing- And if there is, can you give me cost per square foot or yard - A. Probably hydraulic cement mixed with sand, 1 of cement to 2 of sand, makes as good walks as anything' that you can handle. The cement Is about 1.25 per barrel, and 1 l)arrel should make al)out 4 square yards of walk 1 inch to IX' inch thick. Mix dry, and wet and spread quick1y. Smooth with a trowel. (4823) S. Z. asks for a solution for plating metal goods a jet black, that will not peel or crack when said goods are squeezed. A. The coloring of the surface of metals black may be done by chloride of pia- 1893 SCIENTIFIC AMERICAN, INC. tinumand other receipts in our Cyclopedia of Receipts, but do not stand squeezing or pressing without marking the surface. Such surface color should be done after finishing. (4824) F. W. C. says: I am desirous of knowing how to make aluminum present a matted appearance, such as would look well in jewelry. Also, if there is a better material to polish aluminum than rouge. A. The matting of aluminum is done witb polished matting tools or stippled with a broad linmg or stipple, tbe same as silver plate. The tools can be obtained from dealers in jewelers' tools. For the bright finish on aluminum, use Vienna lime after the rouge. (4825) J. T. asks how far a 124 ton gun will throw a projectile, the kind Krupp will exhibit at the World's Fair, also the quantity of explosives to re eachround. A. The 124 ton gun is intended to carry solid shot of half a ton with a charge of 700 pounds of powder, with a range of 12 or 13 miles. (4826) C. E. E. asks: What can I use for the porous cup in a battery - What will do that I can find here without buying one- A. Porous flower pots may be used for the porous cells of batteries by stopping the hole in the bottom of the pot. Such porous cells, however, are not as efficient as those made for the purpose. (4827) S. B. write: We have two large iron columns, one on each side of boilers, in basement, both essential supports to a six story building. They get very hot. Will you please advise us if expansion and contraction of same is any indication of danger - A. There is no danger,from the influence of thetheat, if the columns are outside of the brickwork of the boiler setting.
