89-4

THEORY AND PRACTICE OF ENGINEERING.

Book II.

valuations should never be entrusted to the uninitiated, or to those who have not madebuildings their particular study.

Mills and buildings, where there is water-power, require to be valued under (two heads :first, the buildings by their cubical content; then the water-power; to establish that of thelatter, it must be first ascertained whether the water acts by its weight or gravity, aswith a breast or overshot wheel, or by impulse, as in undershot wheels. In the former,or gravity wheels, their diameter must be ascertained, as well as the breadth, thedepth of the shrouding, and the number of buckets ; also the velocity of the wheel, orthe number of revolutions it makes in a minute when at work ; the fall of water perpen-dicularly, which is the difference of level between the centre of the column of water asdelivered on the wheel and its lower periphery: the section of the water in the troughwhere it is conducted to the wheel, and its velocity, must be determined by ascertainingthe number of seconds a floating body requires to pass through a given distance. Inundershot water-wheels, their diameter must be taken, the breadth, the depth of thefloatboards, and their number; also the velocity of the wheel, its fall, and the section andvelocity of water in approaching the wheel.

In Corn and Flour-mills the valuator must examine their actual state, and whether themillstones are new or old, whether the mills are ever stopped by back-water in floods,or retarded from other causes: in estimating the value, the power of a horse is equal toraising 33000 lbs. 1 foot high in a minute. One pair of millstones in a flour-mill, with itsattendant bolting and other machinery, worked by a water-wheel, is considered to beequal to an 8-horse power. The value of the water-power capable of working a pair ofmillstones with the attendant machinery night and day all the year round, in some situationsis valued at 20 1. per annum, and sometimes more or less, according to circumstances.The full amount of working time is usually taken at twenty-two hours during the day andnight, two hours being allowed for the change of men and other contingencies: millstonesnot actually -at work should not be counted. It often happens that a mill has abundanceof water for only six months in the year, and is at a considerable distance from a markettown; wherever this is the case, and land carriage is considerable, an allowance must bemade for every mile of additional distance of a shilling or more in the pound*, where a millis 10 miles from a market town, it can be rarely worked to advantage. To determinethe value of a flour-mill, the number of pair of millstones usually worked at a time mustbe ascertained, as well as their diameter. The force necessary to work a pair of corn mill-stones grinding meal, together with a pair of shelling and attendant machinery, is taken some-times at only 6-horse power : the number of pairs of grinding mill-stones, shelling-stones,and other machinery in the mill, as well as the ordinary working time, must be alsoascertained. To determine the water-power of corn-mills where there is one pair ofstones, tables are usually made, calculated upon the performance of an 8-horse power engine.

Bleaching Mills. In beetling mills in a single long engine the wiper beam, or that whichis furnished with cogs for lifting the beetles, is usually 10 feet long, and makes 30 revolu-tions in a minute; being furnished with two sets of cogs on its circumference, it raisesthe beetle sixty times in a minute; such a wiper beam working beetles of 4 feet 4 inches inlength, and 3 inches in depth from front to rear, making thirty revolutions, or lifting thebeetles sixty times in a minute 1 foot high, is equal to one-horse power. In this calculationthe power necessary for working the traverse beam, which holds the linen, is included; anallowance is made for the guide slips, which retain the beetles in a perpendicular position.

Tables may be made upon the above data for any length of beetles, where the numberof inches from front to rear are given; and the horse-power may be set down. Todetermine the value of the other machinery in a bleaching mill, it is usuai to considera pair of rub boards eqyal to two-thirds of a horse-power ; a pair of wash feet equal to onehorse-power ; a starching mangle, one horse-power; a drying and squeezing machine equalto one horse-power; and a calender from three to eight horse-power, according to itsquality.

Flax Mills. Six stocks are considered to require the power necessary to turn a pair ofcorn millstones with shelling-stones, fans, sifters, and other attendant machinery; thereforeeach stock is equal to one horse. The bruising machine, consisting of three rollers, maybe considered equal to one and a half stocks.

Spinning Mills. Coarse yarns require a greater proportionate power than fine; thisis chiefly owing to the additional trouble necessary to prepare the coarser kinds for thespindle; the spindles and their machinery are also heavier.

Yarn is distinguished by its degrees of fineness, and known by the number of leas orcuts it yields to the pound: a bundle is twenty hanks ; a hank is twelve leas or cuts, anda cut is 300 yards in length.

Tow is usually spun at from 2 to 5 leas to the pound, and in the dry way, includingthe carding and preparation, it requires a horse-power to 40 throstle spindles.

Coarse Yarn , from 13 to 18 leas to the pound, including the preparation, requires a horse-power to 80 spindles.