Lectures on Natural Philosophy

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1851 Excerpt: ...33,000, by the product of the area of the piston, the distance traversed by the latter during a stroke, and the number of strokes per minute.f Example.--The number of strokes, to be made by an engine, is 27; the diameter of the cylinder must be 37 inches; the length of the stroke 76 inches; and the horse power 100: --what must bo the pressure, per square inch? The area of the piston is 1075 2126 inches; the distance to be traversed by the piston, during each stroke, 12-7 feet: --and 100x33000 nl, 1075-2126 x 12-7 x 27= 9 lbS 62. It is to be remembered that, in calculating as above, the loss of force which arises from various causes--and makes the effective very different from the nominal horse power of the engine--have not been taken into account. The steam, having been heated in contact with water, it cannot have its temperature reduced, without suffering partial condensation: for, none of its pressure arises from its having been expanded, while in the gaseous state. Loss of power, therefore, is caused in this way by radiation, during the passage of the steam from the boiler to the cylinder. There is a loss of the steam which is in the passages, when a communication between the cylinder and atmosphere, or condenser, is opened: and also of that, however small, which is between the piston and end of the cylinder, when the motion of the former is reversed. The steam, thus unavoidably wasted, is called the clearance. Steam is wasted, also, to a greater or less extent, by leakage. In addition to all this, power is expended in overcoming the. . _ _ padn Yw Smce57P=V'- = 5 t Since 57 Y=Pdn--P0 friction of the piston against the cylinder, and that of the various joints, &c.: likewise, in working pumps, &c. 63. Every cubic inch ...