Part 229

The _Alpha_-rays have a velocity of from 1.56 × 10₉ centimeters per second (radium) to 2.25 × 10₉ centimeters per second (thorium); they are particles of helium carrying a double charge of electricity. _Beta_-rays have a greater range of velocity and approach that of light. Both _Alpha_- and _Beta_-rays are absorbed by a thickness of one centimeter of lead, but _Gamma_-rays pass through an inch of lead; they carry no charge of electricity, yet ionize the air and discharge the electrometer.

All the rays on impinging on solid particles give rise to _secondary rays_, sometimes called _Delta_-rays, electrons moving with comparatively low velocity. The _Alpha_-rays possess ninety-five per cent of the energy evolved and produce brilliant fluorescence in zinc sulphide, diamond, etc., the other rays producing this best in willemite and the platino-cyanides; all become absorbed and transmuted into heat.

Radium every hour generates sufficient heat to raise its own weight of water from freezing to boiling point.

THE SPINTHARISCOPE.--This is a simple piece of apparatus invented by Sir William Crookes, by means of which some of the effects of the _Alpha_-ray particles can be observed in a very striking manner. It consists of a little screen covered with powdered zinc sulphide. A small fragment of radium is placed directly in front of the middle of the screen and in close proximity to it. On observing this screen in the dark through a suitable lens, scintillating little points of light are seen to be continually flashing into view and dying away. Each tiny spark is thought to be produced by the impact of a single _Alpha_-ray particle. That these particles or emanations must be matter in a state of extreme attenuation is proved by an experiment of Professor Curie’s in which a box constructed of platinum was pierced with two holes so minute as to be capable of retaining a vacuum, and yet these radium emanations passed through quite freely.

_What are the medical uses of radium?_

Ulcerous growths, birth-marks, and scars are beneficially treated, but so far the selective action of radium on tissue has not been determined, nor its bactericidal effect. Its results in the treatment of cancer have not yet reached a definite stage, though it has been widely heralded as a specific for that dreadful malady.

The application of the rays is by various methods: inhalation of the emanation; external application or injection of the emanation condensed on glycerine, vaseline, oil, water, etc.; or the taking of quinine, arsenic, bismuth, etc., on which the emanation has been condensed. Injections of very dilute solutions of radium salts, or insoluble salts suspended in water, are made. But external applications of the rays are considered most important; copper plates or linen are coated with varnish containing the salts, or glass tubes contain them, and the radiations are directly applied, the surrounding parts being protected with lead foil.

HOW TO READ A GAS METER

The dial marked “1 thousand” in the accompanying illustration is divided into hundreds; the dial marked “10 thousand” is divided into thousands; that marked “100 thousand” into ten-thousands, and that marked “1 million” into hundred-thousands. When 1,000 cubic feet of gas have been consumed, the pointer on the dial marked “1 thousand” will have made a complete rotation and the fact will be indicated by the pointer of the next dial at the left, which will point to the figure 1. When 10,000 cubic feet of gas have been consumed, the pointer on the “10 thousand” dial will point to 1, and so on. In reading a gas meter, put down the hundreds first, then the thousands, and so on, always counting the figure just under, or which has just been passed by, the pointer. In the illustration about half a hundred is indicated on the “1 thousand” dial, three thousands is indicated on the next dial, two ten-thousands on the next dial, and one one-hundred-thousand on the “1 million” dial. The reading will be 123,050. The dial marked “ten feet” is called the units dial. It is used for testing the meter to discover whether it is in working order or not. Each mark represents a cubic foot and the complete circle 10 cubic feet. If the pointer moves when no gas is burning, it indicates a leak. If it does not move when the gas is burning, or if its motion is unsteady, it indicates a derangement in the mechanism and shows that the meter requires attention.

=OUTLINE COURSE OF ELEMENTARY SCIENCE FOR THE GRADES=

======+=========================================+===================== GRADES| LIFE | STRUCTURE ------+--------------------+--------------------+--------------------+ | ZOOLOGY | BOTANY | MINERALOGY | | | | | ------+--------------------+--------------------+--------------------+ I.|Observe-- |Observe-- |Observe | II.|1. Birds; migration,|1. Flowers; color, |1. Pebbles and | III.|nesting, feeding. |form, parts. |rocks; color, shape,| |2. Insects; butter- |2. Fruits; color, |hardness. | |flies, moths, earth-|form, etc. |2. Kinds of rock; | |worms. |3. Leaves; shape, |quartzose, calcites.| |3. Uses of birds and|color, veining. |3. Uses; for soil | |insects. |4. Stems; form, po- |making and building.| | |sition, bark, struc-| | | |ture. | | | |5. Conditions of | | | |growth, habits, etc.| | | | | | ------+--------------------+--------------------+--------------------+ IV.|By observing the |Observe characteris-|1. Sandstone | |form and structure, |tics of-- |2. Argillaceous | |determine some |1. Exogens and |rocks. | |1. Orders of mam- |Endogens. |3. Formation of | |mals. |2. Kinds of trees, |rocks. | |2. Orders of birds. |fruits, vegetables, | _a._ Sedimentary; | |3. Orders of |grasses and grains. | sandstone, lime- | |insects. |3. Effects of culti-| stone, etc. | |4. Orders of rep- |vation. | _b._ Igneous; | |tiles. | | granite, etc. | |Uses of animals. | | | | | | | ------+--------------------+--------------------+--------------------+ V.|Characteristics, |Observe characteris-|Formation and uses--| |habits and uses of--|tics-- |1. Coal. | |1. Fishes. |1. Plants of the |2. Mineral oils. | |2. Oysters, crabs, |rose, pine, pulse, |3. Natural gas. | |starfishes. |violet, pink, mus- |4. Iron; ores. | |3. Coral animals. |tard, composite, | | | |lily, grass and fern| | | |families. | | | | | | | | | | | | | | | | | | | | | | ------+--------------------+--------------------+--------------------+ VI.|Characteristics of |Peculiarities, |1. Minerals and | |Animals of the-- |habits, uses-- |mines of the United | |1. Temperate cli- |1. Palm, banana, |States. | |mate. |pineapple and orchid|2. Gold and silver. | |2. Tropical climate.|families. |3. Copper. | |3. Polar climate. |2. Mosses; lichens. | | |Uses made of them. | | | | | | | | | | | | | | | ------+--------------------+--------------------+--------------------+ VII.|Animals of the dif- |1. Zones of vegeta- |Mines and minerals | |ferent zones of the |tion. |of other countries. | |Old World compared |2. Limits of migra- | | |with those of the |tion. | | |United States. Dis- |3. Vegetable pro- | | |tribution and migra-|ducts of commerce. | | |tion; cause; limits.| | | | | | | | | | | | | | | | | | | ------+--------------------+--------------------+--------------------+ VIII.|Relation of animal |1. Culture of |Minerals. | |life to vegetation |fruits, vegetables, |1. Constituents. | |and civilization. |fibers, grains. |2. Commercial value | |Checks on animal |2. Commercial value;|and uses in the | |life. |benefits to man. |arts, etc. | | | | | ------+--------------------+--------------------+--------------------+

======+============================================================== GRADES| STRUCTURE ------+--------------------+--------------------+-------------------- | GEOLOGY | PHYSICS AND | ASTRONOMY, | | CHEMISTRY | METEOROLOGY ------+--------------------+--------------------+-------------------- I.|Rain; its effects-- |Observe qualities; |Observe-- II.|1. On the surface; |elastic, porous, |1. Sun, moon, con- III.|slopes, ponds, in |etc. |stellations. |valleys, streams. |1. Forms of water; |2. Wind, clouds, |2. Below the sur- |their uses. |rain, snow, frost, |face; springs, cav- |2. Atmosphere; |dew. |erns, etc. |weight, composition.|3. Their causes. |River Basins-- |3. Magnetism; elec- |4. Effects. |1. Boundary, uses, |tricity. | |etc. |4. Solutions. | |2. Alluvial de- |5. Gases; hydrogen, | |posits. |oxygen, nitrogen, | | |carbonic acid gas. | ------+--------------------+--------------------+-------------------- IV.|1. Ocean; effects of|1. Heat; sources: |Climate; causes: |waves, tides, |sun, fuel, friction.|1. Winds, direction |currents. |2. Transmission; |of sun’s rays. |2. Glaciers; mo- |conduction, radia- |2. Surface; moun- |raines: formation, |tion, convection. |tains, vegetation. |effects. |3. Uses: warming, |3. Bodies of water; |3. Volcanoes; gey- |cooking, smelting. |rivers, ocean |sers; earthquakes. |4. Physical and |currents. |4. Gradual elevation|chemical changes |Twilight; duration. |and depression of |observed. | |the earth’s crust. |5. Carbon; forms; | | |uses. | ------+--------------------+--------------------+-------------------- V.|Continent building--|1. Light-- |1. Prevailing winds. |1. Mountains, | _a._ Sources; |2. U. S. weather |plains, coast lines.| uses. |maps. |2. Agencies; | _b._ Transmission,|3. Climate of the | _a._ Vegetable; | reflection, re- |United States. | peat-bogs, swamps.| fraction. | | _b._ Animal; coral| _c._ Lenses, | | formation, shell | glasses. | | deposits. |2. Fermentation of | | _c._ Chemical |fruit juices; yeast.| | springs, geysers, | | | caverns, deposits | | |in lakes and seas. | | ------+--------------------+--------------------+-------------------- VI.|1. Appalachian and |1. Magnetism; uses: |North and South |Rocky mountains. |compass, electro- |America-- |2. River basins and |magnets. |1. Winds; trades, |great lakes of the |2. Electricity; |polar, variable. |United States. |sources and uses. |2. Wind zones. | |3. The levers; |3. Weather maps. | |scales. | | |4. Equilibrium of | | |bodies. | | |5. Chlorine. | ------+--------------------+--------------------+-------------------- VII.|Continent struc- |Pendulum; inertia, |Trades and Monsoons. |ture-- |motion. |1. Deserts; Sahara, |1. South America. |Forces: gravitation,|Arabia, etc. |2. Eurasia. |cohesion, chemical |2. Heavy rains of |3. Australia. |attraction. |India. |4. Africa. |Capillary attrac- | | |tion; osmose pres- | | |sure and flow of | | |liquids. Testing air| | |and water for | | |impurities. | ------+--------------------+--------------------+-------------------- VIII.|The earth; form, |Sound; propagation, |The Solar system. |crust-- |reflection, vibra- |The moon. |1. Rock strata; |tion, music. |The sun; fixed |fossils. |Examination of |stars. |2. Geological ages. |soils. |The tides; ocean | | |currents. ------+--------------------+--------------------+--------------------

SOME GREAT MECHANICAL INVENTIONS

STEAM ENGINES

_What are steam engines?_

_Steam engines_ are machines in which the elastic force of steam is used as a motive power. In the ordinary engines the alternate expansion and condensation of steam imparts to a piston an alternating rectilinear motion, which is changed into a circular motion by means of various mechanical arrangements.

The engine is unquestionably the grandest and most influential for good of all the great inventions in the realm of physics. No other contrivance of man can be compared with this gigantic, yet tractable motor, in relieving both man and beast of ceaseless toil and irksome drudgery; in preventing suffering and starvation, and promoting intercourse, progress and civilization among the nations of the earth.

_Give a description of the steam engine._

Every steam engine consists essentially of two distinct parts: the apparatus in which the steam is produced, and the engine proper. We shall first describe the former.

STEAM BOILER.--The boiler is the apparatus in which steam is generated. Usually a cylindrical boiler is used for fixed engines; those of locomotives and of steam vessels are very different.

The steam is produced from water at a pressure considerably above that of the atmosphere, and is delivered to the engine with as little loss of pressure and heat as possible. The higher the pressure of the steam, the greater will be the amount of heat available, in a given weight of steam, for conversion into mechanical energy. Only a fraction of the total heat energy given to the steam in the boiler is converted into the mechanical work in the engine. By far the greater portion still remains in the steam after it has passed through the engine. The proportion of heat utilized depends on the thermal efficiency of the engine, amounting from twelve to fifteen per cent in good condensing engines; in the very best engines of large size it may be as high as twenty per cent.

The terms axis, axle, arbor, and shaft, in mechanics, are generally understood to mean the bar, or rod, which passes through the center of a wheel. A gudgeon is the pin, or support, on which a horizontal shaft turns; the pins upon which an upright shaft turns are called pivots.

The engine proper consists of a hollow _cylinder_ closed at both ends; inside it is the _piston_, a sliding partition which fits the bore of the cylinder sufficiently close to prevent the steam leaking past it, but having sufficient freedom to allow it to move from end to end of the cylinder with as little friction as possible.

In modern engines the pressure of the atmosphere is not employed to drive the piston down. The steam is admitted into the cylinder above the piston at the same time that it is condensed or withdrawn from below, and thus exerts its expansive force in the returning as well as in the ascending stroke. This results in a great increase of power.

The practical construction of the piston and cylinder, and the arrangement of connecting pipes by which steam is admitted alternately above and below the piston, is fully shown in Figure A. This gives a sectional view of the cylinder, of the piston, and of the distribution of steam. The entire engine is of iron. To the piston, T, is fixed a rod, A, which slides with gentle friction in a tubulure, U, placed at the center of the plate which closes the cylinder. As it is very important that no steam shall escape between the piston-rod and this tubulure, the latter is formed of two pieces, one attached to the plate, while the other, which fits in the first, can be pressed as tightly as is desired, so as to compress the material soaked with fat which is between the two tubulures. This arrangement is called a _stuffing-box_; it prevents the escape of steam without interfering with the motion of the piston.

VALVE-CHEST.--This is the arrangement by which steam passes alternately above and below the piston.

Figure A presents a vertical section of this valve-chest and shows its relation to the cylinder. The steam enters the valve-chest from the boiler by the brass tube _x_. From the valve-chest two conduits, _a_ and _b_, are connected with the cylinder, one above and the other below. If they were both open at once, the steam, acting equally on the two faces of the piston, would keep it at rest. But one of these is always closed by a _slide-valve_, _y_, fixed to a rod, _i_. This moves alternately up and down, by means of an eccentric, _e_, placed on the horizontal shaft. The slide-valve closes the conduit _a_, and allowing the steam to enter at _b_, below the piston, the latter rises. But when it reaches the top of the stroke the rod _i_ sinks, and with it the slide-valve, which then closes the conduit _b_, and allows the steam to enter at _a_. The piston then sinks, and so forth at each displacement of the slide-valve.

It now remains to explain what happens when the steam presses below the piston. It must not remain above, otherwise the piston could not move. But while the steam enters below by the conduit _b_, the top of the cylinder, by means of the conduit _a_, is connected with a cavity, O, from which passes the tube L. Through this tube the steam which has already acted upon the piston passes into the atmosphere, or else is condensed in a vessel filled with cold water, which is called the _condenser_. If, on the other hand, the piston sinks, the vapor below the piston passes, by the conduit _b_, to the cavity O, and to the tube L.

TRANSMISSION OF MOTION.--The alternating rectilinear motion thus generated within the cylinder is transmitted, by means of a rod attached to the piston, to a strong beam _ff_, movable upon a central axis, a system of jointed rods _ee_, called the _parallel motion_, being interposed for the purpose of neutralizing the disturbing action which the circular path of the beam would otherwise exert upon the piston. The reciprocating motion of the beam is now, through the intervention of the connecting-rod _g_ and crank _h_, converted into a circular or rotatory motion, which is rendered continuous and uniform by the fly-wheel _i_, to the axis of which the machinery to be impelled is connected.

The air-pump, _p_, for withdrawing the vapor and water from the condenser, the feed-pump, _s_, for supplying the boilers, and cold-water pump, _t_, for supplying the condenser cistern, are all worked by rods from the beam; and the governor, _u_, for maintaining uniformity of motion, is driven by a band from the crankshaft. The above description refers more immediately to that class of steam engines called _low-pressure_ engines.

TYPES OF ENGINES.--The various forms of the steam engine have received a varied form of classification. There are the general divisions into _condensing_ and _non-condensing_ engines, _compound_ and _non-compound_, and _single_, _double_, or _direct acting_. Again there is the classification connected with the position of the cylinder, as in the _horizontal_, _vertical_, and _inclined_ cylinder engines. Another classification divides steam engines into the uses to which they are applied, such as stationary engines, portable engines, marine, locomotive, electric generating, pumping, mill driving, winding, etc.

STEAM TURBINE.--The steam turbine, though the most modern form of the steam engine in practice, is the most ancient in actual history, the germ of the invention dating from Hero of Alexandria, in the second century B. C.

One kind of steam turbine is really worked on the same principle as a windmill, only steam is used instead of the wind. Instead, however, of the sails making one revolution in seven or eight seconds, it sometimes makes three thousand revolutions a minute, or fifty revolutions a second. In another kind the blades of the turbine are something like the pockets on a water-wheel, and the steam shoves the wheel round by its great velocity.

Turbine engines are now fitted to vessels of large dimensions, up to ocean liners and battleships, with extremely satisfactory results. Turbine engines have also been applied in various other ways, _e.g._, to the driving of fans and blowers.