NO VIMU L4 Smith Gift of Daughter Entered According to Act of Congress, in the year 1881, by JAMES LEFFEL & CO., In the Office of the Librarian of Congress at Washington, D. C. PREFACELIFORNIA No work relating to a special branch of industry has met with a more cordial reception than the large octavo volume entitled "The Construction of Mill Dams," issued by the publishers of the present work in 1874. The size of the former book was due in part to the heavy paper, liberal margins and large type employed; and while these features added greatly to its exterior appearance without affecting its practical value, the price was also necessarily much enhanced. Nevertheless, a large edition of the work, even in this comparatively costly form, was exhausted by the wide and constant demand for a treatise of that kind. This demand had never before been met; no complete work on the subject, and especially none of a strictly practical and useful character, having up to that time been offered to the public. The remarkable popularity of the book, it is believed, was owing not only to the fullness and accuracy of the descriptions given, but also to the fact that technical and abstract terms were as far as possible excluded, and the work rendered practically available to every owner or utilizer of water power. To meet the steadily continued call for the book, the publishers now present a revised edition, at a price which brings it within the reach of all classes, and in a form highly convenient for the purposes of a handbook. They have also consolidated with it another valuable work entitled "Bookwalter's Millwright and Mechanic," in which are contained a large number of Tables and Rules pertaining to Practical Hydraulics, Milling, the Mechanical Trades and General Business, and a variety of Facts, Figures, Methods, Directions and Suggestions, which mechanics of every class, and especially owners or operators of mills, of whatever description, will find of constant use and value. SPRINGFIELD, OHIO. JAMES LEFFEL & CO. 870729 no VIPART I THE CONSTRUCTION OF MILL DAMS. CHAPTER I. MATERIAL AND FORM OF DAMS. The weirs or dams thrown across the beds of rivers have been constructed in a great variety of shapes and of different materials, some of them too costly for general use in a country where small mills are chiefly needed. In cases where the supply of water is large and a high fall is not demanded, a temporary dam composed of boulder stones is sometimes thrown across the stream in a diagonal or slanting direction, and of length considerably greater than its breadth. The water is thus partly forced into the conduit or race above the dam, and the remainder passes over the surface of the dam in a shallow sheet. Being hastily and cheaply built, a dam of this kind may be repaired without much outlay, but the inconvenience of doing this after every heavy rise of the stream is a material drawback on its value. In contrast with this comparatively rude species of dam are those of more solid structure, substantially built of stone, and stretched across the river in the form of a bow, the curve being against the currentthe middle of the dam, in other words, being higher up the stream than the two ends. A dam of this sort, if provided with massive stone abutments, presents a firm resistance to the onset of a flood, and will stand any test ordinarily experienced. It may be made with a gentle slope from the crest both up and down the stream; or with a steep descent on each side, making its walls almost perpendicular; or again with either a steep or sloping front on the upper side and on the lower a curved apron, the wall rounding downward from the top like the lower half of the letter C, by which arrangement the fall is made gradual and its force abated. In a stream of moderate size, a form of weir has sometimes been adopted resembling the letter V, with the apex or point directed up stream. If built upon piles, with a frame of timber forming an inclined plane upon the face of the dam, and filled up with gravel surmounted hu a ass of boulder stones well nacked in, the dam will be nearly impenetrable by water. The position of the two arms of the V distributes the force of the water in passing over, and as the currents descending from either side tend toward the centre of the stream, the banks are less liable to be washed away. If timber is abundant, the frame, instead of having a uniform slope downward on the face of the dam, may be made in a series of steps like a wide stairway, breaking the water into cascades. The piles for such a dam may be placed at right angles with the current, stayed and covered with plank, and made watertight with sheet piling supported by foot piles. Constructed in other respects like the one last described, a dam of this kind will possess great durability and admit of no leakage. An undue accumulation of water above the dam may be remedied by a channel and sluice gate in one of the side walls, by which the surplus water may be drawn off before reaching the crest of the dam. A selfadjusting dam of heavy planks strongly framed together is sometimes stretched across the stream, connected by hinges to the crest of the permanent dam, and held in an upright position by weights passing over wheels on the abutments. In case of a flood the weights give way partially to the increased pressure and the auxiliary dam is let down toward a horizontal position, allowing the water to pass unobstructed. In place of an appendage of this kind, movable flash boards are often used, being held in place by pins and other supports along the brink of the dam, and tightly fitted to each other. În time of low water, the flash boards are of important service in obtaining sufficient head. When the stream rises, the boards are removed (though the supports may often remain) and the crest of the main dam being below high water mark, the surplus water escapes freely. In the following chapters the varieties of dams more practically adapted to the wants of mill-owners in our own country will be mainly considered-including log and frame dams, embankments, crib-work, and their various combinations. We accompany each chapter (with the exception of the 1st and 2d) with a full page engraving, in order to present to the reader more clearly the suggestions we desire to offer. The methods of construction above described are chiefly useful for large establishments and corporations, with whom the matter of expense is not a vital consideration. Our next inquiry will be how the same practical reliability may be obtained, on a smaller scale and with the most moderate outlay. CHAPTER II. MATERIAL AND FORM OF DAMS.-Continued. In many localities where stone is not readily obtained-which is the case in a large portion of the Western States-frame dams are the |