128. Relative to mechanics, what is motion? Motion, in mechanical language, is generally understood an effect of impulsive force, acting in such a manner as to impart either linear or circular velocity by motive power; thus the piston of a steam-engine is made to produce alternate, rectilinear, or reciprocating motion. In the flywheel, through the medium of the crank, is produced uniform circular motion, and by means of cambs, motions to any degree of distortion may be obtained as required.

129. What are the tendencies by high degrees of velocity, on the bearings of shafts in circular motion?

Tendency to heat and become enlarged in diameter, whereby lubrication is diminished in efficiency and friction materially augmented.

130. What is meant by capillary attraction? It signifies a property observable in small tubes, thin flat spaces, porous substances, as sponge, cotton wick, worsted threads, &c., of raising water or other fluids above the natural level; hence the application of the principle for obtaining a continued supply of lubricating fluid between surfaces

in motion, by a syphon-form of worsted threads, one end of which is immersed in oil, the other being inserted and supported by the tube through which the fluid is conducted.

131. In speaking of metals, as gun-metal, brass, bronze, &c., why are they designated alloys?

Because those metals are composed of two or more having a chemical affinity for each other, and hence said to be an alloy, or combined mixture.

Proportions of Metals for the production of various

Machinery

Tough brass

Gun metal

Bell metal

Spelter solder, for iron.

66 harder

Solder for copper

Tinman's solder .

Alloys.

copper 16 copper 10

copper 11

copper 16

copper 1

...

tin 1

39

693

47

266.9
40 268.4 677
41 269.9 662 2.610 74
42 271.4 647 2.670 75
43 272.9 634 2.725 76 309.9
44 274.3 620 2.787 77
45 275-7 608 2.842 78
46 277.1 596 2.899 79
278.4 584 2.958 80

2.493 72

306.1 396

4.363

2.552 73

307.1

391 4.419

308.0 386

4.476

308.9 381

4.535

310.8 372

4.645

311.7 368

4.695

312.6 364

4.747

313.5 359 4.812

Table by which to ascertain the amount of lap necessary on the steam side of a slide-valve to cut the steam off at various fractional parts of the stroke

of its stroke.

To cut the steam off, after the piston has passed through 3 } Multiply the given stroke of the valve by .354 .323 •289 •250 •204 177 .144 and the product is the lap of the valve in terms of the stroke.

Example.-Required the lap necessary to cut the steam off at the end of five-sixths of the stroke, the stroke of the valve being twelve inches, and without lead. 204 X 12 inches.

2.448

As lead is not taken into account because of different quantities being required to different applications of the steamengine, subtract from the lap half the lead; the remainder is the lap required. Thus, suppose the lead equal 25÷2

125 and 2·448 — ·125 — 2.323 inches, the lap with onefourth inch of lead as given.

Table of the Mean Elastic Force of Steam in pounds per square inch, at various grades of Expansion.

Initial density of the steam in lbs. per

Dense steam cut off after the piston has passed through the
following fractional parts of the stroke:

Example.-If dense steam be admitted to the cylinder of an engine at a pressure of 17 pounds per square inch, and cut off when the piston has moved through two-fifths of the stroke, the mean elastic pressure during the whole stroke will be 13.03 pounds per square inch, as obtained by initial 'density and expansive force.