STEAM

, the smoke or vapour arising from water, or any other liquid or moist body, when considerably heated. Subterranean Steams often affect the surface of the earth in a remarkable manner, and promote or prevent vegetation more than any thing else. It has been imagined that Steams may be the generative cause of both minerals and metals, and of all the peculiarities of springs. See Philos. Trans. vol. 5, pa. 1154, or Abr. vol. 2, pa. 833.—Of the use of the air to elevate the Steams of bodies, see pa. 2048 and 297 ib.— Concerning the warm and fertilizing temperature and Steams of the earth, see Phil. Trans. vol. 10, pa. 307 and 357. See also Dr. Hamilton “On the Ascent of Vapours.”

The Steam raised from hot water is an elastic fluid, which, like elastic air, has its elasticity proportional to its density when the heat is the same, or proportional to the heat when the density is the same. The Steam raised with the ordinary heat of boiling water, is almost 3000 times rarer than water, or about 3 1/2 times rarer than air, and has its elasticity about equal to that of the common air of the atmosphere. And by great heat it has been found that the Steam may be expanded into 14000 times the space of water, or may be made about 5 times stronger than the atmosphere. But from some accidents that have happened, it appears that Steam, suddenly raised from water, or moist substances, by the immediate application of strong heat, is vastly stronger than the atmosphere, or even than gunpowder itself. Witness the accident that happened to a foundery of cannon at Moorfields, when upon the hot metal first running into the mould in the earth, some small quantity of water in the bottom of it was suddenly changed into Steam, which by its explosion, blew the foundery all to pieces. I remember another such accident at a foundery at Newcastle; the founder having purchased, among some old brass, a hollow brass ball that had been used for many years as a valve in a pump, withinside of which it would seem some water had got insinuated; and having put it into his fire to melt, when it had become very hot, it suddenly burst with a prodigious noise, and blew the adjacent parts of the furnace in pieces.

Steam may be applied to many purposes useful in life, but one of its chief uses is in the Steam-engine described in the following article.

Steam Engine, an engine for raising water by the force of Steam produced from boiling water; and often called the Fire-engine, on account of the fire employed in boiling the water to produce the Steam. This is one of the most curious and useful machines, which modern art can boast, for raising water from ponds, wells, or pits, for draining mines, &c. Were it not for the use of this most important invention, it is probable we should not now have the benefit of coal fires in England; as our forefathers had, before the present century, excavated all the mines of coal as deep as it could be worked, without the benefit of this engine to draw the water from greater depths.

This engine is commonly a forcing pump, having its rod fixed to one end of a lever, which is worked by the weight or pressure of the atmosphere upon a piston, at the other end, a temporary vacuum being made below it, by suddenly condensing the Steam, that had been let into the cylinder in which this piston works, by a jet of cold water thrown into it. A partial vacuum being thus made, the weight of the atmosphere presses down the piston, and raises the other end of the straight lever with the water from the well &c. Then immediately a hole is uncovered in the bottom of the cylinder, by which a fresh fill of hot Steam rushes in from a boiler of water below it, which proves a counterbalance for the atmosphere above the piston, upon which the weight of the pump rods at the other end of the lever carries that end down, and raises the piston of the Steam cylinder. Immediately the Steam hole is shut, and the cock opened for injecting the cold water into the cylinder of Steam, which condenses it to water again, and thus making another vacuum below the piston, the atmosphere above it presses it down, and raises the pump rods with another lift of water; and so on continually. This is the common principle: but there are also other modes of applying the force of the Steam, as we shall see in the following short history of this invention and its various improvements.

The earliest account to be met with of the invention of this engine, is in the marquis of Worcester's small book intitled a Century of Inventions (being a description of 100 notable discoveries), published in the year 1663, where he proposed the raising of great quantities | of water by the sorce of Steam, raised from water by means of fire; and he mentions an engine of that kind, of his own contrivance, which could raise a continual stream like a fountain 40 feet high, by means of two cocks which were alternately and successively turned by a man to admit the Steam, and to re-sill the vessel with cold water, the fire being continually kept up.

However, this invention not meeting with encouragement, probably owing to the confused state of public affairs at that time, it was neglected, and lay dormant several years, until one Captain Thomas Savery, having read the marquis of Worcester's books, several years afterwards, tried many experiments upon the force and power of Steam; and at last hit upon a method of applying it to raise water. He then bought up and destroyed all the marquis's books that could be got, and claimed the honour of the invention to himself, and obtained a patent for it, pretending that he had discovered this secret of nature by accident. He contrived an engine which, after many experiments, he brought to some degree of perfection, so as to raise water in small quantities: but he could not succeed in raising it to any great height, or in large quantities, for the draining of mines; to effect which by his method, the Steam was required to be so strong as would have burst all his vessels; so that he was obliged to limit himself to raising the water only to a small height, or in small quantities. The largest engine he erected, was for the York-buildings Company in London, for supplying the inhabitants in the Strand and that neighbourhood with water.

The principle of this machine was as follows: H (fig. 3, pl. 27) represents a copper boiler placed on a furnace. E is a strong iron vessel, communicating with the boiler by means of a pipe at top, and with the main pipe AB by means of a pipe I at bottom; AB is the main pipe immersed in the water at B; D and C are two fixed valves, both opening upwards, one being placed above, and the other below the pipe of communication I. Lastly, at G is a cock that serves occasionally to wet and cool the vessel E, by water from the main pipe, and F is a cock in the pipe of communication between the vessel E and the boiler.

The engine is set to work, by filling the copper in part with water, and also the upper part of the main pipe above the valve C, the fire in the furnace being lighted at the same time. When the water boils strongly, the cock F is opened, the Steam rushes into the vessel E, and expels the air from thence through the valve C. The vessel E thus filled, and violently heated by the Steam, is suddenly cooled by the water which falls upon it by turning the cock C; the cock F being at the same time shut, to prevent any fresh accession of Steam from the boiler. Hence, the Steam in E becoming condensed, it leaves the cavity within almost intirely a vacuum; and therefore the pressure of the atmosphere at B forces the water through the valve D till the vessel E is nearly filled. The condensing cock G is then shut, and the Steam cock F again opened; hence the Steam, rushing into E, expels the water through the valve C, as it before did the air. Thus E becomes again filled with hot Steam, which is again cooled and condensed by the water from G, the supply of Steam being cut off by shutting F, as in the former operation: the water consequently rushes through D, by the pressure of the atmosphere at B, and E is again silled. This water is forced up the main pipe through C, by opening F and shutting G, as before. And thus it is easy to conceive, that by this alternate opening and shutting the cocks, water will be continually raised, as long as the boiler continues to supply the Steam.

For the sake of perspicuity, the drawing is divested of the apparatus that serves to turn the two cocks at once, and of the contrivances for filling the copper to the proper quantity. But it may be found complete, with a full account of its uses and application, in Mr. Savery's book intituled the Miner's Friend. The engines of this construction were usually made to work with two receivers or Steam vessels, one to receive the Steam, while the other was raising water by the condensation. This engine has been since improved, by admitting the end of the condensing pipe G into the vessel E, by which means the Steam is more suddenly and effectually condensed than by water on the outside of the vessel.

The advantages of this engine are, that it may be erected in almost any situation, that it requires but little room, and is subject to very little friction in its parts.—Its disadvantages are, that great part of the Steam is condensed and loses its force upon coming into contact with the water in the vessel E, and that the heat and elasticity of the Steam must be increased in proportion to the height that the water is required to be raised to. On both these accounts a large fire is required, and the copper must be very strong, when the height is considerable, otherwise there is danger of its bursting.

While captain Savery was employed in perfecting his engine, Dr. Papin of Marburg was contriving one on the same principles, which he describes in a small book published in 1707, intitled Ars Nova ad Aquam Ignis adminiculo efficacissimè elevandam. Capt. Savery's engine however was much completer than that proposed by Dr. Papin.

About the same time also one Mons. Amontons of Paris was engaged in the same pursuit: but his method of applying the force of Steam was different from those before-mentioned; for he intended it to drive or turn a wheel, which he called a fire-mill, which was to work pumps for raising water; but he never brought it to perfection. Each of these three gentlemen claimed the originality of the invention; but it is most probable they all took the hint from the book published by the marquis of Worcester, as before-mentioned.

In this imperfect state it continued, without farther improvements, till the year 1705, when Mr. Newcomen, an iron-monger, and Mr. John Cowley, a glazier, both of Dartmouth, contrived another way to raise water by Steam, bringing the engine to work with a beam and piston, and where the Steam, even at the greatest depths of mines, is not required to be greater than the pressure of the atmosphere: and this is the structure of the engine as it has since been chiefly used. These gentlemen obtained a patent for the sole use of this invention, for 14 years. The first proposal they made for draining of mines by this engine, was in the year 1711; but they were very coldly received by | many persons in the south of England, who did not understand the nature of it. In 1712 they came to an agreement with the owners of a colliery at Griff in Warwickshire, where they erected an engine with a cylinder of 22 inches diameter. At first they were under great difficulties in many things; but by the assistance of some good workmen they got all the parts put together in such a manner, as to answer their intention tolerably well: and this was the first engine of the kind erected in England. There was at first one man to attend the Steam-cock, and another to attend the injection cock; but they afterwards contrived a method of opening and shutting them by some small machinery connected with the working beam. The next engine erected by these patentees, was at a colliery in the county of Durham, about the year 1718, where was concerned, as an agent, Mr. Henry Beighton, F. R. S. and conductor of the Ladies' Diary from the year 1714 to the year 1744: this gentleman, not approving of the intricate manner of opening and shutting the cocks by strings and catches, as in the former engine, substituted the hanging beam for that purpose as at present used, and likewise made improvements in the pipes, valves, and some other parts of the engine.

In a few years afterwards, these engines came to be better understood than they had been; and their advantages, especially in draining of mines, became more apparent: and from the great number of them erected, they received additional improvements from different persons, till they arrived at their present degree of perfection: as will appear in the sequel, after we have a little considered the general principles of this engine, which are as follow.

Principles of the Steam Engine.

The principles on which this engine acts, are truly philosophical; and when all the parts of the machine are proportioned to each other according to these principles, it never fails to answer the intention of the engineer.

1. It has been proved in pneumatics, that the pressure of the atmosphere upon a square inch at the earth's surface, is about 14 3/4lb avoirdupois at a medium, or 11 1/2lb on a circular inch, that is on a circle of an inch diameter. And,

2. If a vacuum be made by any means in a cylinder, which has a moveable piston suspended at one end of a lever equally divided, the air will endeavour to rush in, and will press down the piston, with a force proportionable to the area of the surface, and will raise an equal weight at the other end of the lever.

3. Water may be rarefied near 14000 times by being reduced into Steam, and violently heated: the particles of it are so strongly repellent, as to drive away air of the common density, only by a heat sufficient to keep the water in a boiling state, when the Steam is almost 3000 times rarer than water, or 3 1/2 times rarer than air, as appears by an experiment of Mr. Beighton's: by increasing the heat, the Steam may be rendered much stronger; but this requires great strength in the vessels. This Steam may be again condensed into its former state by a jet of cold water dispersed through it; so that 14000 cubic inches of Steam admitted into a cy- linder, may be reduced into the space of one cubic inch of water only, by which means a partial vacuum is obtained.

4. Though the pressure of the atmosphere be about 14 3/4 pounds upon every square inch, or 11 1/2 pounds upon a circular inch; yet, on account of the friction of the several parts, the resistance from some air which is unavoidably admitted with the jet of cold water, and from some remainder of Steam in the cylinder, the vacuum is very imperfect, and the piston does not descend with a force exceeding 8 or 9 pounds upon every square inch of its surface.

5. The gallon of water of 282 cubic inches weighs 10 1/5 pounds avoirdupois, or a cubic foot 62 1/2 pounds, or 1000 ounces. The piston being pressed by the atmosphere with a force proportional to its area in inches, multiplied by about 8 or 9 pounds, depresses that end of the lever, and raises a column of water in the pumps of equal weight at the other end, by means of the pump-rods suspended to it. When the Steam is again admitted, the pump-rods sink by their superior weight, and the piston rises; and when that Steam is condensed, the piston descends, and the pump-rods lift; and so on alternately as long as the piston works.

It has been observed above, that the piston does not descend with a force exceeding 8 or 9 pounds upon every square inch of its surface; but by reason of accidental frictions, and alterations in the density of the air, it will be safest, in calculating the power of the cylinder, to allow something less than 8 pounds for the pressure of the atmosphere, upon every square inch, viz 7lb. 10 oz, = 7.64lb, or just 6lb. upon every circular inch; and it being allowed that the gallon of water, of 282 cubic inches, weighs 10 1/5lb, from these premises the dimensions of the cylinder, pumps, &c, for any Steam-engine, may be deduced as follows:— Suppose c = the cylinder's diameter in inches, p = the pump's ditto, f = the depth of the pit in fathoms, g = gallons drawn by a stroke of 6 feet or a fathom, h = the hogsheads drawn per hour, s - the number of strokes per minute.

Then c2 is the area of the cylinder in circular inches, theref. 6c2 is the power of the cylinder in pounds.

And (p2 X .7854 X 72)/282 or (1/5)p2 is = g the gallons contained in one fathom or 72 inches of any pump; which multiplied by f fathoms, gives (1/5)p2f for the gallons contained in f fathoms of any pump whose diameter is p.

Hence (1/5)p2f X 10 (1/5)lb. gives 2p2f nearly, for the weight in pounds of the column of water which is to be equal to the power of the cylinder, which was before found equal to 6c2. Hence then we have the 2d equation, viz, ; the first equation being . From which two equations, any particular circumstance may be determined.

Or if, instead of 6lb, for the pressure of the air on each circular inch of the cylinder, that force be sup- | posed any number as a pounds; then will the power of the cyclinder be ac2, and the 2d equation becomes , by substituting 5g instead of p2.

And farther, .

From a comparison of these equations, the following theorems are derived, which will determine the size of the cylinder and pumps of any Steam-engine capable of drawing a certain quantity of water from any assigned depth, with the pressure of the atmosphere on each circular inch of the cylinder's area.

These theorems are more particularly adapted to one pump in a pit. But it often happens in practice, that an engine has to draw several pumps of different diameters from different depths; and in this case, the square of the diameter of each pump must be multiplied by its depth, and double the sum of all the products will be the weight of water drawn at each stroke, which is to be used instead of 2p2f for the power of the cylinder.

The following is a Table, calculated from the foregoing theorems, of the powers of cylinders from 30 to 70 inches diameter; and the diameter and lengths of pumps which those cylinders are capable of working, from a 6 inch bore to that of 20 inches, together with the quantity of water drawn per stroke and per hour, allowing the engine to make 12 strokes of 6 feet per minute, and the pressure of the atmosphere at the rate of 7lb 10 oz per square inch, or 6lb per circular inch.

A Table of Theorems for the readier computing the
Powers of a Steam-Engine.
1a=(2fp2)/c2=(10fg)/c2=(21fh)/(2c2s)
2c=√((2fp2)/a)=√((10fg)/a)=√((21fh)/(2as))
3f=(ac2)/(2p2)=(ac2)/(10g)=(2ac2s)/(21h)
4g=p2/5=(ac2)/(10f)=(21h)/(20s)
5h=(4p2s)/21=(20gs)/21=(2ac2s)/(21f)
6p=√(5g)=√((ac2)/(2g))=√((21h)/(4s))
7s=(21h)/(4p2)=(21h)/(20g)=(21fh)/(2ac2)
|
Table of the Power and Effects of Steam-Engines, allowing 12 Strokes, of 6 Feet long each,
 per Minute, and the pressure of the Air 7lb 10oz per Square Inch, or 6lb per Circular
 Inch.
The Diameters of the Pumps in Inches.Power of the cylindersand weight of water in pounds.
67891011121314151617181920
The Diameters of the Cylinders in Inches.{307555423327221916141210....5400
31805845352924201715131110...5766
32836147373025211816131210...6144
33906751403.2722191714131110..6534
3494705342342823201815141210..693
35102755745373026221916141311..7350
36.79614839322723201715141210.7776
37.84645141342924211816141211108214
38.88685343353026221917151312108664
39.93715645373227232018161412119126
40.98755948393428242119171513129600
42.1088365534338312723211816141310584
44..9071584841343026232018161411616
46..9978635245373329252119171612696
48...85695749413531272421191713824
50...92756253443834292623211915000
52...100816757484136312825222016224
54....877261524438343027242217496
56....947866564842373229262318816
58....1018370595144393431282520184
60.....8975635548423733302721600
62.....9580685851453935322823064
64......85726254484238343024546
66......90776657514540363226676
68......96827061544842383427744
70.......867564575045403629400
Quan. drawn at one stroke in gallons.7.2101316.22024.228.833.839.24551.257.864.872.280
Quan. drawn in one hour in hogsheads.82114148184228276328385447513583659738823912
Diameter of pumps.67891011121314151617181920
|

Let us now describe the several parts of an engine, and exemplify the application of the foregoing principies, in the construction of one of the completest of the modern engines. See fig. 4. pl. 27.

A represents the fire-place under the boiler, for the boiling of the water, and the ash-hole below it.

B, the boiler, filled with water about three feet above the bottom, made of iron plates.

C, the Steam pipe, through which the Steam passes from the boiler into the receiver.

D, the receiver, a close iron vessel, in which is the regulator or Steam-cock, which opens and shuts the hole of communication at each stroke.

E, the communication pipe between the receiver and the cylinder; it rises 5 or 6 inches up, in the inside of the cylinder bottom, to prevent the injected water from descending into the receiver.

F, the cylinder, of cast iron, about 10 feet long, bored smooth in the inside; it has a broad flanch in the middle on the outside, by which it is supported when hung in the cylinder-beams.

G, the piston, made to sit the cylinder exactly: it has a flanch rising 4 or 5 inches upon its upper surface, between which and the side of the cylinder a quantity of junk or oakum is stuffed, and kept down by weights, to prevent the entrance of air or water and the escaping of Steam.

H, the chain and piston shank, by which it is connected to the working beam.

previous entry · index · next entry

ABCDEFGHKLMNOPQRSTU and VWXYZABCEGLMN

Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

This text has been generated using commercial OCR software, and there are still many problems; it is slowly getting better over time. Please don't reuse the content (e.g. do not post to wikipedia) without asking liam at holoweb dot net first (mention the colour of your socks in the mail), because I am still working on fixing errors. Thanks!

previous entry · index · next entry

STAR
STARLINGS
STATICS
STATION
STATIONARY
* STEAM
II
PP
STEELYARD
STEEPLE
STEERAGE