The Economy of the Short Stroke of Engines In Non-rotary Propulsion. MESSRS. EDITOBB :—Beferring to my former paper on propelling vessels, on page 44, current volume, I now propose to point out a source of waste or non-utilized steam, which, owing to the radical imperfections of the present rotary system, is seldom if ever considered as such, namely, the steam consumed by an unnecessary length of stroke of engine; for if a pressure of 1,000 pounds of steam passing through a distance of i foot, in a given time, will produce the same amount of propulsion that 1,000 pounds passing through 12 feet in the same giveifctime will; theiormer (a short stroke) must be far more economical than the latter (a long stroke). The writers hypothesis is, that the speed of vessels, as relates to distance traveled, is determined by the amount of pounds pressure and the duration of time of such pressure, and not by the distance through which this pressure passes. For instance, supposing a vessels resistance at any given velocity is equal to 1,000 units, the pressure of 1,000 units of power continuously applied during any duration of time, will produce motion at the same rate of velocity whether that power passes through the same or a less distance than that traveled by the vessel. No one will deny that 1,000 pounds pressure is the equivalent of 1,000 pounds of resistance, but many may be of opinion that the pressure, or power, must pass through the equal distance of the resistance overcome, or that if the power passes. through a less distance, the diminution in distance must be made up by an equivalent increase of power. To sustain my hypothesis of the economy of a short stroke and long duration of time—it is necessary to show that neither of the above opinions can be correct. Now as relates to the power passing an equal distance with resistance moved; while in some cases this is strictly correct, as in sailing vessels and boats drawn by horses, yet where steam is used and a lever brought in play, as in paddle wheel and screw steamers, the distance traveled by the power varies from i to -J- that traveled by the body in motion, from which one point at least is certain, namely, that the distance traveled by the vessel does not depend, per se, upon that traveled by the power; —and that diminution of distance does not require an increase of power, I think the following mathematical problem of the dynamic lever and its solution will sufficiently prove: A B represent a dynamical lever attached at A to a short stroke engine, F, working on an axis at C, the crank, A, C, foeing one-eighth the length of the long arm, B C, the lever and engine both being supposed to be attached to a body in motion. The axis, C, being the line of motion is therefore the point of impact of the power and the resistance of body to be moved. This resistance at axis, C, is represented as 70 pounds, while the resistance at the true fulcrum, a circle, B, is represented as 10 pounds, and it is required to move the resistance of 70 to D, without moving the resistance of 10 in the opposite direction of E. Now it is obvious that 75 pounds pressure (over and above friction) applied at A, will overcome the resistance of 70, which will move in the direction of D, without overcoming the resistance of 10 at the circle, B; for the crank being one-eighth, it would require 8 times or 80 pounds, passed through one-eighth the distance to counterbalance the 10. Therefore 75 pounds passed through one-eighth thek distance could not possibly displace the It). Suppose the stroke of engine to be 1 f dot the distance trav- eled by point, B, of long arm of lever would be 8 feet if the resistance of 10 were moved to E, but as these 10 pounds are not displaced, it is obviously impossible for the engine to make its stroke without moving the resistance of 70 to point, D, from which it is easy to see that the resistance at C of 70 has been moved 8 feet to D, while the engine has made its stroke of 1 foot, the power consumed being 75 pounds passed through 1 foot, the effect produced being 70 pounds moved a distance of 8 feet. This being correct (and I respectfully challenge any mathematician or engineer to disprove it), it follows that in propelling apparatus (non-rotary) the distance traversed by the body moved depends upon the pressure applied, and duration of such pressure, rather than upon the length of stroke of en-gine. In further corroboration of- the foregoing permit me to call attention to the fact that in the propelling apparatus of all living creatures the Divine Wisdom has ordained that the power to propel them shall always be applied at the axis or line of motion, hence the wonderful economy of power in nature. In connection with this subject of steam propulsion, permit me to suggest to the leading engineers in the country, that, as it is daily becoming more apparent, with each new improvement in the more economical generation or utilization of steam, that the days of sailing vessels, nd of towing canal boats by horses, are rapidly coming to an end, could some method be invented, saving fifty per cent over any at present in use, th o economy of steam over iil or horses, would at once become so great as to insure its speedy adoption, in which case all the engineers and manufacturing establishments would be taxed to their utmost to supply the demand for engines, boilers, and machinery, for many years to come; hence, if they studied their best interests they would give an atten. tive ear and careful thought to any new invention, by which so desired an end might be possibly accomplished. If our leading engineers would once realize the fact, that the vital principles of all propulsion on land, on water, or ofa bird through the air, is that of the dynamic lever; that though paddle wheel and screw are both dynamic levers, the axis in the paddle wheel is not the fulcrum, but the point of impact of the power and line of motion of the boats resistance; and if the difference between the static and dynamic levers was fully understood, a new era of steam navigation would soon dawn upon the world, and many vast improvements in speed and economy of power be inaugurated for the benefit of mankind at large. p. R. p. New York city. Fastening Beams in Walls. MESSRS. EDITORS :—Having noticed in your paper that the usual custom of building the ends of floor timbers into brick and stone walls, is apt, in case of fire, to thiow over the walls, and that resting the timbers on corbels interferes with the cornice line below, allow me to suggest a cheap mode of obviating these defects. By cut ting the ends of the timbers on a bevel, and laying in the wall as in the inclosed sketch, the cornice line will not be broken, and in case of fire the timbers will fall with little chance of injury to the wall. If in your opinion this plan is novel or useful, please publish for the benefit of all concerned. C. O. Paterson, N. J. How to Make Good Yeast MESSES. EDITORS.—On page 59 of No. 4, for January S8d of this year, in the latter part of Prof. Horsfords lecture on bread, he gives a recipe for yeast which I consider a very poor one, for three reasons. 1st. It requires fresh bakers yeast to start its fermentation. 2d. It will only keep a week in winter, and from two to four days in summer. 3d. If bread made with it is not closely watched, and baked at the critical moment, it will be infallibly sour. The first objection is a serious one out West, on a farm, to wit: How are you to get fresh bakers yeast, when the nearest baker lives may be fifteen miles off? The second and third are equally serious to a woman who has her hands full of work at all times, for she must be making yeast every few. days in warm weather; and when she bakes, be hovering over the stove to watch the loaves and turn them. I now offer you a recipe I brought from England, and which I have used with never-failing success for fifteen years. It is self-fermenting, improves by keeping, and, with its use, it is impossible to make sour bread, unless the flour is sour or the yeast is left uncorked. It will keep for weeks, winter or summer. On Monday morning put two ounces of best bale hops into a gallon and a pint of cold water, boil half an hour, strain hot, and dissolve two ounces of finest table salt and half a pound of A sugar in the liquor; when cooled to new milk warmth, put one pound of sifted flour into a large basin, make a well in the center of it with the hand, and add the liquor by degrees, stirring round and round with a spoon, until the whole of the flour is evenly mixed with the liquor; set the pan with the liquor on a stool by the stove—in winter time day and night. In hot weather this is not requisite On Wednesday morning boil and mash finely three pounds of good potatoes, and mix them with the liquor in like manner a.8 the flour. On Thursday morning there should be a heavy dark scum on the surface. The yeast must now be stirred thoroughly, and strained through a sieve or colander into a gallon jug, corked firmly, tied down, and placed in a cool cellar. Shake well before using. N. D. The liquor should be stirred three or four times a day during the process. A gallon serves my family for sixteen bakings. I use no drugs, as soda, etc., etc., in my bread, nor milk, as that causes bread to dry rapidly. It is best to add a teaspoonful of salt when you bake, and that should be dissolved in a little warm water and mixed with the yeast in j setting the sponge over night. When the bread is once kneaded and put in the pans to rise, it may be left for hours with safety from souring, it will only be too porous. Galena, 111. KIBBY KITTOE, M. D. Suction of Sinking: Bodies. MESSRS. EDITORS :—As the SCIENTIFIC AMERICAN has long since become the institution to which a considerable portion of the Yankee nation look for reliable information relative to scientific questions, I am induced, therefore, to request of you, or some other of your learned correspondents, to inform such of your readers as go down to the sea in ships, whether or not the common assertion and belief is true, that, in onso a vessel founders and sinks at sea, it will produce a downward current or suck, so-called, that will carry with it all j floating obj ects, such as boats, rafts, and persons swimming in the immediate vicinity of the sinking ship. ; W. P. M. [Wo presume there can be no doubt that sinking bodies of considerable bulk do produce a powerful downward current; yet many instances are recorded where a large boat, as a ships long boat, or a raft, has withstood the tendency to go under, the boat, or raft, being on the vessels upper deck at the time of sinking. Small bodies are usually drawn downward, but afterward float. The period of submergence would, however, in most cases destroy human life.—EDS. Gearing—Form of Teeth. MESSRS. EDITORS :—Why are the teeth of wheels made on a curve, is a question which, if propounded to a majority of mechanics, who have almost daily experience on the subject, would not elicit a satisfactory explanation. A few remarks, therefore, on the subject many not be inappropriate. Let the two circles, A and B, represent the peripheries or pitch circles of two wheel, A the driver and B the driven, and the divisions, a 6 c, etc., respectively equal to a V c, etc. Now if power be applied to A, and the friction of the faces of the wheels is greater than the resistance, it is evident that B will revolve, and the points, a a 6 V, etc., will coincide. But when the resistance is greater than the friction, recourse must be had to projections or teeth to prevent slips. Let the right line at the point, a, represent the side of a tooth, as both peripheries are to move at the same velocity, advance the wheels in the direction of the arrows until the points 6 and 6 fall on the line of centers. It will now be observed, while the point a has advanced to g, the side of the tooth has progressed beyond, indicating a tendency to move the wheel, B, at a greater velocity. To prevent this the side of the tooth is required to be curved back to the point, g. Again imagine the wheels to be revolved until the points, c and c, coincide at the line of centers. The point, a, will now have advanced to h, while the side of the tooth represented by E, has traversed a greater distance in order to maintain the relative velocities; it must be curved back to h. Upon advancing the wheels another di- vision, the departure from the curve becomes more apparent. Proceeding to form the tooth, bisect the division, ij, draw the curve found in an opposite direction from the point of bisection; from the center of A, with the proper radius draw an arc cutting the curves, and the point of the tooth is completed. A cavity is now required in the wheel, B, to enable the wheels to revolve. The sides of the cavity are formed by the curve already found extending into the wheel, B,asat g. Bisect the division, g, h, draw the curve in an opposite direction, and the root of the tooth is produced. To construct the tooth of_the wheel, B, it is onjy necessary to revolve the wheels in the opposite direction and repeat the preceding operation. The curve forming the point of tooth of one whel will be a curve for the root of the other. The curves thus-found are the epi-cy cloidal, the proper mathematical curve for me teeth of gearing. In practice the epicycloidal curve is not invariably given to the teeth of wheels, because it is peculiar to the diameters of the Wheels for which it is constructed, and admits of a limited range in case the teeth are wanted to be used for other 166 diameters than that for which they were made. To make patterns or cutters for every pair of wheels that are required would entail great expense on manufacturers, hence they generally have recourse to methods of their own,or use those laid down in text-books, for the purpose of constructing teeth; some of- which, for fine pitches, are almost equal to the epicycloid and admit of more extended application with different diameters. Our method, which I have found to work well in practice, is to lay off the points of the teeth with the pitch, and for the roots, set one point of the compasses in the center of one tooth, and with the other point describe the root of the adjacent tooth; but where the disparity in the diameters is very great, this rule will have to be departed from, especially in large pitches, in which case the tooth of the pinion should be determined first, in order to obtain adequate strength at the root, and the teeth of the large wheel adapted to the peculiar form of the pinions. Bpicyloid teeth, when properly constructed, require no clearance, or at most but a trifle, except at the bottom where good clearance should always be given, as much of the noise heard in gearing running is caused by the teth bottoming, often occasktnedby the shafts springing or the j ournals and boxes wearing. In departing from the epicycloid more clearance should be given between the teeth. The forward side of the driving tooth should come in contact with the rear side of the driven tooth first, and not, as I have observed in some instances, inill-constructed teeth when the reverse was the case, the teeth in first meeting wedging and tending to press the wheels asunder, thereby consuming useful power in doing useless work. More clearance is required when the teeth are cast than when cut. In the former there is always some irregularity, even where there has been the utmost care exercised with the pattern, owing to the unequal contraction of the metal or the rapping of the pattern and mending up of the molds. There are various methods of arranging the teeth of gear wheels, but in every departure fromth-e plain spur there is a measurable amount of detriment. The step gear when a tooth is divided into a series, and each alternate one placed out of line with the other, is a favorite plan with some where heavy work is to be done. But I have failed to be convinced of its superiority over the continuous tooth. Unless set with the greatest accuracy some teeth will sustain more than their proper amount of strain while others will sustain less. These assertions can be verified by any one examining such gear and observing the inequality of the wear. The double oblique tooth is resorted to where strength of tooth is required and and the face limited. In this style the teeth unite in an apex at the center of the face and diverge obliquely with the axis. While this method gives a strong tooth it is a consumer of power as well as a transmitter. Of all the abominations of gearing the single oblique tooth is probably the greatest. In this style of gearing the teeth present inclined planes to each other, and there is a constant tendency in the teeth off or forcing the wheels asunder in a line with the axis, which tendency is ressted by the wheels being secured to the shafts, and a groat amount of power is absorbed by these antagonistic tendencies. I have seen a pair of such wheels, designed by an eminent engineer, absorb half the power of a pair of four-horae trunk engines. Let me here condemn the practice prevailing to some extent of endeavoring to make many teeth bear at the same time. The number of teeth bearing depends altogether on the diameters and pitch, and any attempt to make more teeth bear than these will properly admit of, must necessarily cause a departure from the propar curve of the tooth or a dispropor-tioned length. If strength is the object better give a little more face. Cast teeth when true are much better than cut teeth, the outside scale wearing longer than the softer metal within. Especially are these remarks applicable to bevel gear, in which it is impossible to cut the teeth properly with the means usually employed in cutting engines, owing to the curve of the tooth being a varying one from end to end. After a perusal of the foregoing, the following facts must be impressed on the mind. 1st. The pitch is the arc between the centers of two contiguous teeth, hence the ordinary rule, (Dia. X 3-1416) -v- pitch = No. of teeth, or (Dia. X 31416) -H No. of teeth = pitch, is the proper one. 2nd. The plain spur is the bsst form of a, gear wheel. J. C. Washington, D. C. Window Glass. MESSES. EDITORS :—I read in your last number a description of How Window Glass is Made, which, though I have read many similar before, seems to me now so awkward in process—not in description—that I cannot help entering my protest against the idea, though it seems to be a fact, that there has teen no essential improvements in glass making since the time the Arabs camped, and burnt seaweed, etc. —you all know the story of its discovery. To take a lump of viscid tenacious material on the end of an iron tube, and blow it, and twirl it into such a shape that it is possible to snake it flat, after a deal of further trouble, and this to be the :onlj means of effecting this result now known, seems to me tto be a disgrace to American inventive genius. Why ennnot a pot of melted viscid substance like glass be. lrawn out iilto sheets, as well as a continuous sheet of paper from the tank fall of pulp, or a continuous lead pipe from a erueible full of melted lead. Guessing, a priori, I Should say much easier, and. bettej-, and smoother, for the substance to toe worked is of just the right natsre to yield with ease and without danger to Jjhe manipulations of machinery, and be worked into all shapes, without breakage or chemical corrosion. But, will say the glass workers, it _js the excessive temperature a wliiehit must be worked that is the difficulty. My friends, if it took a machine as heavy as a Pondrinier paper machine, and all made of platinum, it seems to me it would pay if a sheet of glass could be run out like a sheet of paper, and I believe it can, and will be done some time. I have seen a glass thread spun at the rate of many thousand yards a minute, and it seems to me a sheet is only, theoretically, a multitude of threads. When we open up the immense soda and potash fields of the Western desert, and when the pine forests and other timbers are exhausted, the question, of what shall we build houses, and construct a great many other things, now made of wood, will lie between glass, iron, and paper. Cheap soda, potash, and fuel, and a glass (paper) machine to make it on, will decide the question in favor of this indestructible material, so far as it is applicable. Who is there that has capital and spunk enough to try the experiment ? A small apparatus to run out a sheet ten inches wide, made of platinum, and set in the furnace, running out a stream of window glass, through proper orifices and annealing ovens, I believe to be a possibility, and a-not far distant accomplishment. C. BOYNTON. A Good Puddling Furnace. MESSES. EDITORS :—I notice in a late number of the SCIENTIFIC AMEEICAN, an extract from an English paper showing the extraordinary economy of E. B. Wilsons patent puddling furnace now in use in England and elsewhere. It seems, however, that the consumption of sixteen hundred weight of coal to the tun of puddled bars, is about the best that can be averaged, with his furnace, running night and day. This shows a great saving over what has been used as a general thing in England, or wherever coal is cheap; but it is not so economical as a double puddling furnace built in the Cold Brook Iron Works, this place, by Mr. John Wilson, an English furnace builder, now here: This furnace made 42 tuns 10 hundred weight of six inch bars (Scotch pig iron) with 27 tuns of coal, I think half Cumberland and half Pictou, equal to 13 hundred weight and three-quarters to the tun of 2,240 pounds. I doubt if a more economical furnace has ever been built. E. G. S. St. John, New Brunswick. Poor Work on Agricultural Machines. MESSES. EDITOES.— Fulton under the head of Good Agricultural Machinery in your issue of Jan. 23, page 54, cur rent volume, says he noticed an article headed Poor Mechanical Work on Agricultural Machinery referring to issue of Dec. 16, volume XIX, page 393, which he claims does a great injustice to a large class of manufacturers, etc. I noticed the same article and was greatly pleased that your ever-welcome paper should speak a word on that subject in the way of relief to the. farmer. As I was born and raised on a farm I have had considerable experience with agricultural machinery and can testify, as well as all other farmers, that nine-tenths of the machinery sold us are made only to sell and not to fit,Pulton to the contrary notwithstanding. I never have soen a reaper that could be set up and run without the aid of a file or cold chisel, and sometimes new holes have to be made in order to get in some of the bolts; as was the case with some half an acre of reapers painted in high colors and shipped to this place last season, in pieces, to be set up from the pile, not one of which could be set up without the assistance of a whole kit of blacksmith and carpenter tools. While it is necessary that the greatest skill should be exercised in constructing this class of machinery, which is subjected to constant jerks and strains of different parts, by its movements over uneven ground, and being in all sorts of positions, the mechanical workmanship is fully developed only in other classes of machinery that set firmly on their feet or ride on easy springs. The prices that farmers have to pay for their machinery would warrant a better class of work. WESTEEN FARMER. Waakon, Allamakee Co., Iowa. THE SCIENTIFIC AMERICAN.—In these days, when new and worthless publications are being thrown on the market by the score, it is with a pleasing satisfaction that we come face to face with our old, tried, and trusty friends. We have not yet reached that millennial period in newspaperdom when a successful journal is born in a day. The process is like the processes of nature : first, the blade, then the ear, and then the full corn in the ear. Among the newspaper successes in this country, none is more noteworthy than the SCIENTIFIC AMEEICAN. For an American journal it is old in years, but young in strength and vigor, leaving all its imitators and would-be rivals, and there is a host of them, in the distance. It is safe to say that there is a degree of freshness, strength, and originality in the SCIENTIFIC AMEEICAN that are found no where else among journals professing to occupy a similar sphere. A complete file of this paper from the original date of publication, would be a library in itself.—American Builder AETIFICIAL EBONY.—This substance, now used to a considerable extent in Europe, is said to be prepared by taking sixty parts of seaweed charcoal, obtained by treating the seaweed for two hours in dilute sulphuric acid, then drying and grinding it, and adding to it ten parts of liquid glue, five, parts gutta-percha and two and a half parts of India-rubber, the last two dissolved in naphtha; then adding ten parts of coal tar, five parts pulverized sulphur, two parts pulverized alum, and five parts of powdered rosin, and heating the mixture to about 300 degrees Fahrenheit. We thus obtain, after the mass has become cold, a material which, in color, hardness and capability of taking a polish, is equal in every re-epaet 9 ebony, and much Cheaper.
This article was originally published with the title "Correspondence"