(1) Detroit asks whether a boat propelled with a force of 3 miles an hour on still water will with the same propelling force run 6 miles an hour in a current running 3 miles an hour?  A. We think so.

(2) J. C. R asks: Which was the first railroad built in the United States? That is, a regular, incorporated road, connecting two points, and conveying passengers, freight, etc.  A. We believe that the road now known as the Baltimore and Ohio Railroad was the first in the United States chartered for carrying on a general transportation business.

(3) J. R. E. asks how to make an ordinary sunshade for a telescope when placed, and what kind of glass it is composed of.  A. Any very dark glass will answer, providing it is perfectly plane. It should be placed between the eye and eyepiece.

(4) W. H. G. S. writes: I wish to give a blue color to screw heads, wire and steel. What shall I use?  A. Heat them in a sand bath, or apply shellac or copal varnish, to which a little Prussian blue has been added.

(5) T. McW. asks (1) for a good recipe for making Babbitt metal.  A. By weight, 4 parts copper, 8 parts antimony, 96 parts tin. 2. What is meant by heating surface in boilers, and how is it computed?  A. The term heating surface, as ordinarily used, refers to the surface which has water on one side, and flame or the products of combustion on the other. 3. I have a peculiar kind of steel which I cannot harden by fire and water, neither will it caseharden by prussiate of potash. What can I do with it to harden it?  A. Assuming your account to be correct, we judge that you cannot harden it.

(6) A. Van B. writes: A correspondent in your last issue asks how to keep rubber belts from slipping. Mine slipped considerably, but I checked it by throwing powdered rosin in between the belt and pulley while running. The pulley soon becomes covered with a tough black coating, very much like leather, and there is no more slip. [This expedient can be used to advantage in certain cases, but it is better to have a belt large enough to drive without using any preparation.—Ed.]

(7) E. B. C. asks: 1. Does a more powerful battery produce better results in telephone or microphone?  A. A powerful battery is not required for either. 2. Can you give me a short description of the principle and construction of the aerophone?  A. We think it has not been perfected.

(8) A. T. L. asks for a recipe for a liquid boot or shoe polish.  A. Clausen's ink is made as follows: Nutgalls, 8 parts; logwood extract, 10 parts; boil together in water, q. s., and add Castile soap, 4 parts; glycerin, trace. Crocker's—Logwood extract, 6 ozs.; water, 1 gallon; ivory black, 1.5 oz.; glycerin, 1 oz.; bichromate of potassa, 0.125 oz.; copperas, 0.125 oz.; boil together. Sefton's—Orange shellac, 64 ozs.; alcohol, 4 gallons; pure asphaltum, 60 ozs.; neat's foot oil, 1 pint; lampblack, q. s. Ovington's—Water, 1 gallon; logwood extract, 6 ozs.; water, 1 gallon; borax, 6 ozs.; shellac, 1.5 oz.; water, 0.5 pint; bichromate of potassa, 0.375 oz. Mix the solutions, and add 3 ozs. ammonia. Shaw's—Borax, 3 ozs.; orange shellac, 5 ozs.; water, q. s.; boil and add soluble aniline black or nigrosine, q. s. Rub the spots with strong aqueous solution of ferric chloride, and dry before applying the dressing.

(9) J. S. & R. M. write: 1. We propose putting in a steam engine of 20 horse power, and we are informed there is an engine that weighs 2,700 lbs., that has a balance wheel weighing 500 lbs., cylinder 10 x 10 inches; cutting off at ¾ stroke, running at 180 to 200 revolutions a minute, and they say that it is 20 horse at 70 lbs. steam. Will such an engine develop 20 horse power?  A. The engine would develop 20 horse power under the above conditions, if well constructed. 2. How can we calculate the power of an engine?  A. To determine the power of an engine, multiply the mean pressure on the piston in lbs., by the piston speed in feet per minute, and divide the product by 33,000.

(10) A. L. G. asks: 1. With a boiler 15 inches in diameter by 30 inches in height, with five 1½ inch tubes 18 inches long, firebox 12 x 12, and all made of iron plates ¼ inch thick. What is the greatest number of pounds of steam to the square inch it will hold, and what fraction of a horse power will it give to an engine having a cylinder 2 x 4 inches, situated 2 feet from the boiler, and connected by 40 inches of steam pipe?  A. You can carry 150 lbs. of steam, and might develop 1 horse power. 2. What is meant by the pitch of a wheel in a propeller, and what is the inclination of a cylinder?  A. The pitch of a propeller is the distance it would advance in the direction of its axis at each revolution, if it worked without slip. The inclination of a cylinder refers to the angle made by its axis with a horizontal or vertical line.

(11) J. H. asks: 1. Has steel been used for portable boilers?  A. Yes. 2. What size boiler is required for an engine having a 3 x 4 inch cylinder?  A. Diameter, 24 inches; height, 45 inches; heating surface, 65 to 70 square feet.

(12) J. A. M. asks: How large must an air pump be for an engine steam cylinder 8 x 8, making 100 revolutions per minute with 90 lbs. of steam, allowing the pump to be 4 inches stroke, double acting, to be attached to surface condenser?  A. Diameter, 3½ inches.

(13) J. A. F. asks: 1. What shall I paint my boiler and smoke stack with, and where can I get the paint? My engine is a thrashing engine, and of course is out of doors during the fall of the year.  A. Get some black varnish made from petroleum, from a dealer in machinists' supplies. 2. How shall I care for the boiler inside?  A. Leave the boiler perfectly dry, unless you can coat the interior with oil. 3. What shall I do for the engine. Is it necessary to take the piston out of cylinder and oil it?  A. If the engine is to stand for some time, remove the piston, coat it and the cylinder with tallow; the same for the journals. Cover all finished parts of the engine with a mixture of white lead and tallow. 4. I find my steam gauge does not indicate less than 10 lbs. when boiler is cold. What is the trouble and how can it be repaired?  A. In such a case it is best to send the gauge to a maker for repairs.

(14) "Zebra" wishes to know the best test of the genuineness of white lead; also the simplest way to try the comparative value of two samples of ground white lead. Also the name of the best work to consult upon the manufacture of Portland cement.  A. See answer No. 29, p. 283, current volume, Scientific American. Also pp. 102-105 Normandy and Noad's "Commercial Analysis." The relative value of different samples of white lead in oil is roughly judged from the weight of a given measured quantity, the covering properties when compared on glass with a sample of finest white lead, and the color and general appearance of the sample. You may consult Reid's "Manufacture of Portland Cement."

(15) J. B. B. asks: Can I arrange an electric battery so as to heat a platinum wire for the purpose of cutting wood? Is it practicable?  A. Two or three Bunsen cells will do it. It is impracticable save as an experiment.

(16) D. S. M. asks how to color butter to make it yellow, without injuring it in any way.  A. A little annotto is often used. If pure, it is not injurious.

(17) H. C. M. asks: What substances are there that will absorb light during the day when exposed to light, and give it out again at night? A. 1. Heat strontium theosulphate for fifteen minutes over a good Bunsen gas lamp and then for 5 minutes over a blast lamp. 2. Heat equal parts of strontium carbonate and lac sulphuris gently for 5 minutes, then strongly for 25 minutes over a Bunsen lamp, and finally 5 minutes over a blast lamp. 3. Precipitate strong aqueous solution of strontium chloride by means of sulphuric acid, dry the precipitate, and heat it to redness for some time in a current of hydrogen, then over a Bunsen lamp for 10 minutes, and for 20 minutes over a blast lamp. Mix any of these with pure melted paraffin for use as a paint, and expose for a time to sunlight. The two former yield a greenish phosphorescence in the dark, the latter a bluish light.

(18) Z. asks: Is the Great African Desert below the level of the sea, and if so, could it be made into an inland sea by flooding from the ocean?  A. A considerable, though relatively small, portion of the Sahara is below the sea level, and the flooding of the lowest portion has been proposed. The greater part of North Africa lies at a higher level, the exception being a chain of old lake beds or chotts on the border of Algeria.

(19) J. P. L. asks: How can I make a filter to cleanse rain water from smoke as it passes from the roof to the cistern? The coal which is burned here (bituminous) gives us a great deal of trouble in this regard.  A. The carbonaceous matters may be removed by passing the water through a large barrel half filled with fine gravel and pounded, freshly-burnt charcoal (free from dust), distributed in alternate layers, each several inches deep. Over this spread a clean piece of bagging, and fill in with fine gravel or coarse clean quartz sand for 12 inches or more. The inlet pipe should discharge at the bottom of the barrel—the filtered water flowing from the top.

(20) F. E. H. asks: Can percussion caps be so composed as to explode when pierced by a sharp pointed needle? If so, of what should they be composed?  A. Such an arrangement is employed in the needle gun. The composition may be of mercuric fulminate.

(21) C. A. N. asks: What is the horse power of an engine 30 inches stroke, 14 inches cylinder, 51 revolutions per minute, 60 lbs. mean pressure in cylinder?
A. Piston area = 153.94 square inches. Piston speed = 255 feet per minute.

(22) P. O. asks: If I admit steam 100 lbs. pressure in a cylinder 15 x 24 inches, and cut the steam off when piston has traveled 6 inches, what will be the pressure at 6 inches, 12 inches, 18 inches, and 24 inches, or just before it exhausts?  A. The pressure will vary about in the inverse ratio of the volume, so that, approximately,

(23) H. T. S. asks: What size should I make the holes in the side of a fan wheel, 20 inches in diameter? Also what size should the nozzle be?  A. Allow an opening of from 17 to 20 square inches at inlet and discharge.

(24) E. M. D. writes: I am constructing a telephone according to directions in Scientific American Supplement No. 142, using a bar magnet in place of horseshoe magnet and soft iron core. 1. Would it reduce the strength of bar magnet to cut a thread on one end of it?  A. No. 2. Will a bar magnet, used in Bell telephone, lose its power to such a degree as not to work?  A. Not readily. 3. Is No. 22 copper wire of sufficient size for a telephone line of 1,000 feet?  A. Yes; but larger would be better.

(25) S. & Y. write: We have a pair of burrs on which we grind plaster. The burrs are about 4 feet in diameter and 1½ foot thick. We are running them as an over runner at this time, but wish to change them and make the lower burr run instead of the upper. Can a pair of burrs of the above size be run in that way, and if so, what is the maximum speed at which they can be run?  A. If properly arranged, you can run them, after the change, as fast as is allowable for overrunning stones.

(26) J. J. asks: Which tire makes a wheel the strongest, 1.25 x 0.50 inch iron, or 1.25 x ⁵⁄16 steel tire?  A. The steel tire will be the strongest, comparing good qualities of steel and iron.

(27) E. L. W. asks: Is a ton (2,000 lbs.) of first class coke equal in heat giving power to a ton (2,000 lbs.) of coal? If not, please give me the relative value of coke and coal in heat giving power?  A. Calling the evaporative power of good anthracite coal 1, good bituminous coal rates at about 0.92, and coke from 0.89 to 0.95.

(28) J. W. S. asks what to impregnate paper with to give it an agreeable smell while burning.  A. You may try a strong ethereal or alcoholic solution of benzoin, tolu, storax, olibanum or labdanum. To burn well the paper should first be impregnated with an aqueous solution of niter and dried.

(29) M. G. asks whether hydrogen and oxygen can be produced as rapidly and copiously in the decomposition of water by the galvanic battery as by the action of sulphuric acid on zinc or lead in the one case, and by heating chlorate of potassa in the other.  A. Yes, with a very powerful current.

(30) T. G. H. asks for names of useful treatises on mechanical movements.  A. "Scientific American Reference Book," and "507 Mechanical Movements."

(31) R. B. T. writes: We have just set up a new engine; the cylinder is 8 x 12, has a common slide valve. We think the valve is too short; it is set 0.125 inch open when on center, takes steam 10 inches before cutting off; the exhaust is very free. The engine runs about 110 revolutions per minute. We think we could save steam by using a longer valve, and cut-off about ⅝ stroke, and make the exhaust space in the valve shorter, so that it will shut in a portion of the exhaust and form a cushion for the piston. About how much of the exhaust can we shut in without overdoing it?  A. You can obtain a good action by making the ratio of compression equal to the ratio of expansion, with the proviso that the final cushion pressure must not exceed the initial pressure.

(32) D. B. L. writes: Our boiler after being repaired was tested at 110 lbs. cold water pressure. Three days after it gave out where it was repaired at 58 lbs. steam pressure. To find the leak we put on 80 lbs. cold water pressure, and could not find it. We then put steam pressure at 40 lbs., which made the leak very great, whereas with cold water pressure we could find none. Can you explain it?  A. The phenomenon is probably due to the change of shape in the boiler when heated.

(33) F. C. writes: Our engine is a plain slide valve engine, 24 x 9, steam following almost to end of stroke. How shall I make a valve to cut off at ¾? Our exhaust now is 1 inch, steam ports 0.75, bridges 0.75. Length of valve 4½ inches, cavity 2⅜, travel of valve 2 inches. Will I have to enlarge the steam chest; the valve uses the whole length of it now?  A. As the length and travel of valve must be increased, it will be necessary to lengthen the steam chest, unless you can apply an independent cut-off valve.

(34) T. P. writes: A small basement room 9 feet high is to be heated by a furnace in an adjoining room. By carrying the hot air pipe through the partition midway between the floor and the ceiling it will stand at an angle of about 45°. If carried through at the top of the room it will of course be nearer vertical. In which position of the hot air pipe will the room be most easily heated?  A. Place the hot air pipe in the position first described. Take the cold air from a point near the floor through a flue opening above the roof.

(35) G. M. P. asks: What is a good and cheap substitute for salt for raising the temperature of water to 230° Fah.?  A. An oil bath is often used instead. Chloride of calcium will answer as well as salt, though not so cheap.

(42) J. M. B. asks: What will prevent the hair from falling out?  A. Keep the pores of the skin open by frequent bathing and change of underclothing. Bathe the head with clean soft water, and stimulate the scalp with a moderately stiff brush morning and evening. The head should be occasionally cleansed with a weak solution of glycerin soap in dilute spirit of wine, with care to remove all traces of soap from the hair. Use no pomades or oils of any kind.

(43) B. H. P. asks (1) how to make malleable iron, such as used in wrenches.  A. Malleable iron castings are made from mottled iron. They are cleaned by tumbling and then packed in iron boxes with alternating layers of rolling mill scale. The boxes are carefully luted and packed in an annealing furnace, where they are kept at a white heat for a week or more, and then allowed to cool gradually. 2. How is steel or iron made to adhere to the face of the jaws of the wrench?  A. By welding.

(44) J. G. E. asks: What is the highest column of water that can be raised from a well by means of a siphon pump with 60 lbs. steam, likewise a 1 inch column of water with 60 lbs. steam?  A. Lift, from 26 to 27 feet.

(45) W. H. W. asks: 1. Is there any solution excepting rubber that will make cloth thoroughly waterproof, or at least withstand the attack of water for an hour or so? It should be applied by dipping the cloth in the solution.  A. Linseed oil boiled with a little wax and litharge is useful for some purposes. Cloth prepared with paraffin, balata gum, the gum of the asclet pias or milkweed, naphtha solution of the dried pulp of the bamboo berry, anhydrous aluminum soaps (see pp. 149 and 159, "Science Record," 1874), are also employed. 2. Is there any chemical that could be combined with the solution, imparting some property to the same for which rats or mice would have an antipathy so as to prevent their attacks?  A. A trace of phenol will generally suffice.

(46) J. L. asks: Is the balata gum softened by animal oils or fat?  A. Yes.

(47) P. L. W. asks. What distance would a 100 lb. weight have to fall to run a sewing machine for 5 hours?  A. For an ordinary family sewing machine, requiring about one thirtieth of a horse power, the weight would have to fall about 3,300 feet in the 5 hours.

(48) W. G. R. asks: 1. What is the valve yoke of a steam engine?  A. We presume you refer to the rectangular yoke that receives the back of the valve in the class of engines having balanced valves. 2. What should be the diameter of the bore of an engine of 1 horse power with 100 lbs. pressure, also the length of stroke?  A. Diameter, 2¾ inches; stroke, 4½ inches. 3. How are the back gears of a lathe made so as to be thrown out of gear when it is wished to use the lathe at a high speed?  A. Ordinarily by a cam and lever, or tight and loose joint. 4. Would ¹⁄64 of an inch thickness of sheet steel be strong enough for the boiler of a small model locomotive? How much pressure would it stand to the inch?  A. If the diameter does not exceed 3 inches, you can carry a pressure of from 50 to 60 lbs. per square inch.

(49) J. W. W. asks: Which will stand the most pressure, a piece of round iron 1 inch long and 1 inch in diameter, or a piece of gas pipe the same dimensions, both being set upon end?  A. The round iron.

(50) W. M. B. writes: 1. I have one eighth inch basswood, cherry, butternut and walnut. Which do you advise for the sounding board of a microphone and Hughes telephone?  A. Either will do, but pine or spruce is better. 2. Would a glazed earthen jar do for the outside of battery described in Scientific American Supplement, No. 149?  A. Yes. 3. Could I make insulated wire myself? If so, how?  A. Wire may be insulated by giving it a coat of shellac varnish and allowing it to become dry and nearly hard before winding.

(51) W. H. S. asks how to satin finish tubing like sample sent.  A. The specimen has been electro-plated with silver in the usual manner, and the electric current then reversed for a few moments, thus redissolving a portion of the plate, the remainder presenting the peculiar satin like luster.

(52) S. W. C. asks: Has carbon for telephone purposes ever been made by subjecting the black deposited by a flame to a heavy pressure?  A. Yes. Edison's carbons are made in this manner.

(53) "Hardware" asks: 1. Where is best to take hot air in a room, at register near ceiling or in floor?  A. At or near the floor. 2. Where is best place to have ventilation, near floor or near ceiling? A. If connected with a flue having a good draught it should be near the floor.

(54) R. W. J. asks: What causes the cracking noise in the pipes of a steam heating apparatus, when a fire has been started to warm up the building? Is it the water in the pipes made by condensed steam, or is it the expansion of the pipes from being heated?  A. The noise is due to both causes in some degree, but principally to the water, which produces violent blows.

(55) C. N. A. asks how to temper steel tools for working on stone or similar work. There is some preparation which is put in water which accomplishes the purpose when the steel is heated and plunged in.  A. Heat the tools to a cherry red, and plunge in clean, moderately cool water. A little common salt is sometimes added to the water.

(56) G. B. asks: 1. Is the height to which water is raised by a hydraulic ram measured from the ram itself or from the spring from which the supply comes? A. From the ram. 2. Can a hydraulic ram be constructed to discharge 1,000 gallons of water per minute?  A. Yes.

(57) L. D. writes that benzine will answer much better to exterminate roaches, moths, etc., than anything else. It will not hurt furniture in the least, will evaporate, and can be easily applied.

Minerals, Etc.—Specimens have been received from the following correspondents, and examined, with the results stated:

M. B. W.—No. 1 is a silicious clay—it might be useful in the manufacture of some grades of pottery, etc. No. 2 is a ferruginous shale—contains about 80 per cent. of silica and 10 per cent. of alumina, besides lime, magnesia, iron oxide, and water.—W. S.—It is fibrous talc—talc of good quality is in considerable demand for paper making and other purposes.—W. G. H.—The sand contains no precious metal—the glittering particles are mica.—S. F.—The specimen you send consists of a mass of the long hairs which have been attached to the seeds of the "milkweed" (asclepias), or, as it is sometimes called, from the silky nature of these appendages, "silkweed." We believe that this material is put to no other economic use at present than that of a filling for cushions and pillows. The beauty of this silk like down long ago attracted attention, and many unsuccessful attempts have been made to put it to some practical use in the arts; but, as you have probably noticed, the hairs are both brittle and weak, and an examination with a lens will show that it wants the roughness and angularity necessary to fit it for being spun like other fibers. It has, however, been mixed with cotton and woven into fabrics having a silky luster and capable of taking brilliant dyes, but the manufacture has never been prosecuted. The plants, though widely distributed over the United States, and quite common, are nevertheless not abundant enough in a wild state to afford much of a supply, and we believe no experiments have been made in cultivating them.

Any numbers of the Scientific American Supplement referred to in these columns may be had at this office. Price 10 cents each.

COMMUNICATIONS RECEIVED.

The Editor of the Scientific American acknowledges with much pleasure the receipt of original papers and contributions on the following subjects:

Manufacture of Porous Cups for Tyndall Grove Battery. By W. H. S.
Cylinder Condensation. By F. F. H.
Sawdust. By W. H. M.
Keely Motor. By G. R. S.
Firing. By A. P. A.
Steam Launches. By G. F. S.

HINTS TO CORRESPONDENTS.

We renew our request that correspondents, in referring to former answers or articles, will be kind enough to name the date of the paper and the page, or the number of the question.

Many of our correspondents make inquiries which cannot properly be answered in these columns. Such inquiries, if signed by initials only, are liable to be cast into the waste basket.

Persons desiring special information which is purely of a personal character, and not of general interest, should remit from $1 to $5, according to the subject, as we cannot be expected to spend time and labor to obtain such information without remuneration.

English Patents Issued to Americans.

From November 8 to November 12, inclusive.

Electric light.—T. A. Edison, Menlo Park, N. J.
Feed water apparatus.—S. J. Hayes et al.,———.
Pipe, manufacture of.—W. Radde, N. Y. city.
Potato digger.—L. A. Aspinwall, Albany, N. Y.
Refrigerator.—J. A. Whitney, N. Y. city.
Screw cutting machinery.—C. D. Rogers, Providence, R. I.
Sewing machine.—Wilson Sewing Machine Company, Chicago, Ill.
Wire machinery.—C. D. Rogers, Providence, R. I.

[OFFICIAL.]

INDEX OF INVENTIONS

FOR WHICH

Letters Patent of the United States were

Granted in the Week Ending

October 15, 1878,

AND EACH BEARING THAT DATE.

[Those marked (r) are reissued patents.]

A complete copy of any patent in the annexed list, including both the specifications and drawings, will be furnished from this office for one dollar. In ordering, please state the number and date of the patent desired, and remit to Munn & Co., 37 Park Row, New York city.

TRADE MARKS.