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Let us take for example one of the 240 horse-power Babcock & Wilcox boilers here in the University. The height of the columns may be taken as 4½ feet, measuring from the surface of the water to about the center of the bundle of tubes over the fire, and the head would be equal to this height at the maximum of circulation. We should, therefore, have a velocity of 8(4½)^{½} = 16.97, say 17 feet per second. There are in this boiler fourteen sections, each having a 4-inch tube opening into the drum, the area of which (inside) is 11 square inches, the fourteen aggregating 154 square inches, or 1.07 square feet. This multiplied by the velocity, 16.97 feet, gives 18.16 cubic feet mingled steam and water discharged per second, one-half of which, or 9.08 cubic feet, is steam. Assuming this steam to be at 100 pounds gauge pressure, it will weigh 0.258 pound per cubic foot. Hence, 2.34 pounds of steam will be discharged per second, and 8,433 pounds per hour. Dividing this by 30, the number of pounds representing a boiler horse power, we get 281.1 horse power, about 17 per cent, in excess of the rated power of the boiler. The water at the temperature of steam at 100 pounds pressure weighs 56 pounds per cubic foot, and the steam 0.258 pound, so that the steam forms but 1/218 part of the mixture by weight, and consequently each particle of water will make 218 circuits before being evaporated when working at this capacity, and circulating the maximum weight of water through the tubes.

And because the breath of flowers is far sweeter in the air (where it comes and goes like the warbling of music) than in the hand, therefore nothing is more fit for that delight, than to know what be the flowers and plants that do best perfume the air. Roses, damask and red, are fast flowers of their smells; so that you may walk by a whole row of them, and find nothing of their sweetness; yea though it be in a morning's dew. Bays likewise yield no smell as they grow. Rosemary little; nor sweet marjoram. That which above all others yields the sweetest smell in the air is the violet, specially the white double violet, which comes twice a year; about the middle of April, and about Bartholomew-tide. Next to that is the musk-rose. Then the strawberry-leaves dying, which yield a most excellent cordial smell. Then the flower of vines; it is a little dust, like the dust of a bent, which grows upon the cluster in the first coming forth. Then sweet-briar. Then wall-flowers, which are very delightful to be set under a parlor or lower chamber window. Then pinks and gilliflowers, especially the matted pink and clove gilliflower. Then the flowers of the lime-tree. Then the honeysuckles, so they be somewhat afar off. Of beanflowers I speak not, because they are field flowers. But those which perfume the air most delightfully, not passed by as the rest, but being trodden upon and crushed, are three; that is, burnet, wildthyme, and watermints. Therefore you are to set whole alleys of them, to have the pleasure when you walk or tread.

The drums are of three sheets, of such thickness as to give the required factor of safety under the maximum pressure for which the boiler is constructed. The circular seams are ordinarily single lap riveted though these may be double lap riveted to meet certain requirements of pressure or of specifications. The longitudinal seams are properly proportioned butt and strap or lap riveted joints dependent upon the pressure for which the boilers are built. Where butt strap joints are used the straps are bent to the proper radius in an hydraulic press. The courses are built independently to template and are assembled by an hydraulic forcing press. All riveted holes are punched one-quarter inch smaller than the size of rivets as driven and are reamed to full size after the plates are assembled. All rivets are driven by hydraulic pressure and held until black.

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