Chapter V: Part 5

We come now to a new and distinct era in the history of this important invention, and in noticing the labours of Mr. Watt, we may almost speak of his engine as the gigantic offspring of a hand giving birth to an automaton, no less powerful than that of the fabled enchanters of the olden time.

Mr. Watt's first great improvement in the engine of Newcomen may be best understood by reference to the annexed diagram, in which _a_ represents the cylinder, and _b_ its plug or piston made to fit air-tight. The pipe _d_ is furnished with a stop-cock, by means of which the elastic vapour is occasionally admitted.--A similar pipe, furnished with a stop-cock at _f_, passes from the other side of the cylinder, and enters the vessel _g_; _e_ being the reservoir to contain water.

If we now suppose the piston at the bottom of the cylinder, and steam admitted by the pipe _d_, its expansive force will elevate the piston, and when the air is expelled, the whole internal cavity of the tube will be filled with condensible vapour. On closing the steam-cock, and opening that connected with the vessel _g_, a portion of the vapour will immediately expand itself, and coming in contact with the cold sides of the vessel, a portion of its heat must be absorbed by the water at _e_. A new portion of steam then descends, and is also condensed, and indeed the same process continues till the whole of the steam is drawn from the tube. A vacuum being thus formed, the pressure of the atmosphere will preponderate, and the piston rod be depressed to the bottom of the tube. On closing the stop-cock _f_, a new supply of steam may be admitted by the other pipe, and after raising the piston, the process of condensation may be readily repeated.

The advantages that arise from this mode of forming a vacuum are very considerable, not the least important of which, is a saving of nearly half the fuel.

In the old engine, the condensing water must reduce the temperature of the internal surface of the cylinder to that of the atmosphere, before a vacuum could be produced, and when the condensing water was applied more sparingly, the elastic vapour remaining in the cylinder was found to materially reduce the pressure of the air operating above. From this it will be seen that the great advantage of Mr. Watt's apparatus consists in performing the condensation in a separate vessel, so that the cylinder is always preserved at the temperature of boiling water.

Having thus produced a vacuum without the intervention of condensing water beneath the piston, Mr. Watt's next improvement consisted in closing the top of the cylinder, so that the piston-rod worked through an air-tight hole in the centre of the cap; and to ensure the necessary pressure within the cylinder, steam with an elastic force greater than that of the atmosphere was admitted above the piston. The atmospheric engine of Newcomen was thus converted into a steam-engine, and its power was easily regulated.

A cylinder and piston constructed on the most improved principles may now be examined.

In the annexed diagram, the cylinder A is furnished with a steam-tight piston, the rod of which is supposed to be connected with the working beam. B represents the pipe which admits the steam from the boiler, the quantity being regulated by the throttle valve _c_, and the elastic vapour is now passing through the box _d_ _d_, so that it enters beneath the piston. At the same instant of time, a communication is formed through the aperture _m_ _n_ to the pipe _p_, which leads to the condenser. When the piston reaches the top of the cylinder, the sliding bridge or valve has its direction changed, so that the pipe _r_, and consequently the bottom of the cylinder, is connected with the condenser, while a passage is opened from the pipe _m_ _n_ to the steam box. Thus a communication is alternately made between the top and bottom of the piston.

The slide-valve represented above is not invariably employed in the double-acting engines, and we frequently find the annexed contrivance resorted to, in some of the best engines.

The pipe 14 represents the passage to the cylinder, and a communication is now opened with the steam chamber _g_. The raised valve is perforated and a similar valve beneath closed by the rod which passes through it. On closing the valve _g_, the lower valve _h_ is opened, and a free passage between the condensing pipe beneath and the upper part of the cylinder is the result. If we now suppose a similar double valve placed at the bottom of the cylinder, it will easily be seen that an effect similar to that described in the sliding valve will be produced.

The speed of the engine is regulated by a very ingenious contrivance introduced by Mr. Watt, called the _governor_, and represented beneath.

The balls _i_ _i_ are supported by the bent levers _h_ _f_, and as they are made to revolve with the fly wheel axis, by means of a band passing round the pulley _c_, any increase in the speed of the engine will cause the balls to diverge. The moment this takes place, the shorter arm of the lever _n_ is depressed, and as the extremity _l_ is connected with the steam-pipe by the throttle valve, the supply of steam must of necessity be diminished, and the speed of the engine reduced.

As the working power of the engine depends very materially on the accurate fitting of the piston, it may be adviseable to examine some of the modes of effecting this important object.

Mr. Smeaton, who greatly improved the atmospheric engine, coated the under side of the piston with elm or beech planks about two inches thick; the wooden bottom being screwed to the iron with a double thickness of flannel and tar, to exclude the air between the iron and the wood. By the adoption of this improvement, its property of conducting heat was reduced, and the wood having been previously jointed, with the grain radiating in all directions from the centre, was not liable to expand by the heated steam. This piston was kept air-tight by a small stream of water continually falling on its upper surface; but in Mr. Watt's engine he was compelled to make the piston fit tight without any other media than the oil that was employed to lubricate it.

The piston is now cast with a projecting rim at bottom, which is fitted as accurately as possible; the part above the rim being about four inches less than the cylinder, thus leaving a circular groove for the hemp which forms the packing. To keep this in its place, a lid or cover is put over the top of the piston, with a projection which enters into the circular groove for the packing, and pressing upon it, the plate is forced down by screws, which work into the body of the piston. By this means the packing is made to fill the internal part of the cylinder with tolerable accuracy, and thus prevents for a time any steam passing between the piston and the cylinder. When, however, by continued working, the packing ceases to fit, it occasions a waste of steam, to remedy which, the cylinder cap must be removed, and as this is attended with a considerable degree of trouble to the engine-man, it is seldom attended to till a considerable loss of power has arisen. There are two improvements on the piston, by which this inconvenience is to a certain extent obviated.

In the first, by Mr. Woolfs, each of the screws is furnished with a wheel or nut, and these are all connected together by means of a central wheel, working loose upon the piston-rod in such a manner, that if any one of the screws be turned, a similar motion is given to the remainder.

In a piston thus constructed, there is little difficulty in drawing down the packing, by applying a key to the square head of the projecting screw, employed to communicate with the rest: the key-hole being afterwards closed by a cap.

The second contrivance is by Mr. Barton, a diagram of which, accompanied by a piston as it is usually constructed, is shewn beneath.

In the first piston, the screws _i_ _i_ are made to compress the packing _h_ _h_, by acting upon the plate _n_ _n_, the piston-rod _r_ being firmly attached by the nut _c_.

In one of the modifications of _Barton's piston_, on the contrary, the packing is dispensed with, as the flexible springs _t_ _t_ _t_ press upon the wedges _c_ _c_ _c_, and expand the intermediate plates. A break-joint is readily formed, by making the series of plates double; the second set of plates falling upon the spaces which occur between the first row.

The action of the _high pressure_ engine depends upon the great elastic force acquired by steam, when exposed to the action of heat at very high temperatures.--It may indeed be considered as a return to the principle of Brancas and the Marquis of Worcester, as in this engine no condensing water is necessary; and it acts merely by the elastic or repellant force of steam. In the high pressure engine, the condenser is taken away; and the steam, instead of being converted into water by artificial cold in a close vessel, is allowed to escape into the atmosphere from one side of the piston, while it is acting forcibly on the other.

The advantages of the high pressure engine over that used with a condenser, are cheapness in construction, and a saving of the whole expense attendant on procuring a sufficient supply of condensing water, which in some cases is an object of considerable importance.

In the annexed section, the piston _B_ passes through an air-tight stuffing box, and the steam is entering beneath it, by the four-way cock _E_. If we now suppose the piston at the top of the cylinder, a new arrangement of the communicating pipe takes place, as the steam which was beneath escapes, while a fresh supply enters above. The four-way cock may be best explained by a section in the opposite direction. Two pipes are seen at the lower extremity of the cock, which communicate with the upper and under sides of the piston. The aperture _D_ opens to the air, while the pipe _C_ serves for the admission of steam from the boiler.

We have now to notice the double cylinder engine constructed by Woolfs, which will be found, by reference to the diagram in the preceding page, to consist of a high pressure cylinder, connected with a condensing apparatus.

A and B represent the two cylinders, in the larger of which the steam is allowed to expand itself, after passing from the high pressure cylinder B. The steam, which in the first instance is of considerable elasticity, is admitted to the cylinder B, by the tube and valve E, and entering the cylinder above its piston, impels it to the bottom. When this is effected, a communication is opened between the upper part of the cylinder B, and the under side of the cylinder A. The communication between the cylinder B and the steam-pipe E, is now reversed, and the steam is made to press on the under side of the piston B, a communication being at the same time formed between the upper part of the cylinder A, and the pipe leading to the condenser which is seen beneath. So that if we suppose the two pistons connected by means of their rods with one end of an ordinary working beam, the upward and downward strokes of each will be performed at the same time. We have hitherto considered the steam as passing direct from the boiler to the cylinder B; this, however, is in reality effected by a more circuitous route, as it is in the first instance admitted to the steam-case of the larger cylinder by the pipe C, and passing round a similar case, encircling the cylinder B, it is then made to enter at E. The pipe at D is merely intended to form a communication for carrying back to the boiler any water that may be produced by condensation in the steam-case, before the engine arrives at a proper temperature for working.

Having thus briefly examined the nature of Mr. Woolf's engine, it may now be advisable to revert to the boiler, by which he proposes to generate steam of sufficient elasticity for the use of the small cylinder, which requires elastic vapour of great expansive force. The boiler, represented by the diagram beneath, consists of a series of tubes, of cast-iron, connected by screw-bolts with the under side of a larger vessel A A, communicating with the engine. The upper boiler is furnished with four, and in some cases, with five apertures; the first of which is intended for the admission of water, to supply the waste which continually arises from evaporation. The safety valves, man-hole, and water-pipe are also shewn.

The mode of setting this boiler is also of considerable importance, as it is advisable to give a long and waving course to the chimney.

A A still represents the principal boiler, while the figures 1, 2, 3, &c. indicate the passage of the flame and heated air; a section of the chimney being shewn at O.

The steel-yard safety-valve which was employed in all the early engines is simple, and the nature of its construction may readily be understood. A represents a portion of the upper part of the boiler; B the safety-valve or plug made to fit air-tight on the valve-seat beneath; C the lever working on its axis at D, and furnished with a moveable weight E, adjusted to balance the pressure of steam within the boiler.

When steam of great elasticity is required, the weight is placed at the extremity of the lever, and as such, acts with greater force on the safety-valve, than when removed to a point nearer to the axis on which it revolves: so that should _low_ pressure steam, or that which has a less expansive force, be required, it will only be necessary to remove it nearer towards the axis on which it turns.

The lever and balance-ball safety valve already described, appear but little calculated for those engines in which high pressure steam is employed, as the engine-man, in an over anxious zeal for the full performance of the machinery confided to his care, has been frequently known to increase the internal pressure of a large boiler many thousand pounds beyond the resistance to which it was originally proved. To prevent a recurrence of those accidents, which first drew the attention of the legislature to this important part of the engine, it appears advisable to inclose the safety-valve in an iron case, of which a section is annexed.

The valve _B_ in this case rests upon a conical seat in the boiler _A_, and is furnished with a series of small moveable plates lettered _c_, which are employed to increase or diminish the entire weight of the safety-valve, the whole being covered by the box _D_; and as this is pierced with a number of small holes, the steam readily escapes when the expansive force exceeds the resistance offered by the loaded valve.

The patent _revolving wheel_ invented by Mr. Masterman, appears to promise the best results of any rotatory engine yet invented, the friction being much less than in any other apparatus in which steam is employed as a prime mover. In this engine, Mr. Masterman proposes to employ water, or the fluid metal mercury as the immediate agent, which he effects by inclosing it in the tubular rim of a large wheel, furnished with valves opening in one direction. This wheel, as is shewn in the opposite diagram, is made to revolve on a hollow axis connected with the steam boiler. The arms or spokes which radiate from the axis are also hollow; and on the admission of steam from the boiler, it is conducted through the arm immediately opposite, and entering the rim of the wheel, comes in contact with, and presses against the column of water beneath and the closed valve above the arm. The water being previously heated to the boiling point, no condensation ensues, but the whole weight of water, which was previously balanced in two columns of equal height, is driven, by the pressure of the steam, to the side opposite to that at which the elastic vapour entered, and that side of the wheel will necessarily preponderate. If this process be repeated, the steam being allowed to blow through each radiating arm in succession, a continuous rotatory motion will be produced. Should it be advisable to employ steam of less elasticity, a condenser may be added, and that too without materially increasing the expense.

The application of steam-engines to the _propelling_ of _carriages_ on the public road, has hitherto been considered as a refinement in mechanics, rather to be wished for than a matter of reasonable expectation. The _locomotive_ engine was first employed for this purpose by Messrs. Trevithick and Vivian, in 1802; and it found a ready introduction to the mining districts where rail-roads are general. In some cases, five, six, and even ten waggons laden with coal are dragged up an inclined plane by means of these vehicles; and of course impelled by a high pressure engine, from the utter impossibility of carrying condensing water in a moveable vehicle.

An engine of four horses' power, employed by Mr. Blenkinsop, impelled a carriage lightly loaded on a rail-road at the rate of ten miles an hour, and when connected with thirty coal waggons, each weighing more than three tons, its average rate was about one-third of that pace.

When the locomotive engine was first tried, it was found difficult to produce a sufficient degree of re-action between the wheels and the tract road; so that the wheels turned round without propelling the vehicle. This inconvenience was, however, obviated by Mr. Blenkinsop, who, when he adopted the locomotive engine, took up the common rails, on one side of the whole length of the road, and replaced them by a series of racks, or rails, furnished with large teeth. The impelling wheel of the engine was made to act in these teeth, so that it continued to work in a rack which insured a sufficient degree of re-action.

From the great weight of an ordinary _locomotive engine_ as well as the construction of its impelling wheel, it must be evident that the employment of this species of prime mover on the public roads would be in the highest degree destructive; and as such that its use will for some years to come be partially confined to the mining districts, in which the greatest facilities are offered for its general adoption. Indeed, we find in one neighbourhood alone, and within a space of less than thirty square miles, more than twenty miles of road admirably adapted for this species of conveyance; and it is a well known fact, that there are many situations in which iron rail-roads might be advantageously employed, in which it would be quite impossible to open a navigable canal. In illustration of the above fact, it may be proper to state, that a company, with a large capital, is now forming for the express purpose of facilitating the conveyance of goods by locomotive engines.

The mode of applying the steam-engine to the purposes of navigation is equally simple with its employment in our manufactures.

It is generally supposed that the _steam-boat_ is of very recent invention; on the contrary, however, the possibility of employing steam as a prime mover in the propelling of vessels was suggested as far back as the reign of Charles I.

In one of the old tracts preserved in the library of the London Institution there is a very curious representation of a steam-boat, constructed by an engineer of the name of Hulls. And this individual, now so little known, was undoubtedly the first who applied a steam-engine to the purpose of navigation.

To impel a vessel by this means, two paddle wheels, like those used in an under-shot water-wheel, are connected by means of a long axis and crank, with the working beam of the steam-engine; and if this motion is not found sufficiently rapid, a wheel and pinion are added, which, although it _decreases_ the effective power of the engine, yet _increases_ the velocity of the paddle wheels.

To illustrate the great advantages possessed by the steam-engine, even in its rudest state, over every other species of prime mover yet enumerated, it may now be advisable to examine its effective force when employed in the working of pumps. It has been found that one hundred weight of coals burned in an engine on the old construction, would raise at least _twenty thousand cubic feet_ of water twenty-four feet high; an engine with a twenty-four inch cylinder doing the work of _seventy four horses_. An engine on Capt. Savery's plan, constructed by Mr. Keir, has been found to raise nearly _three millions_ of pounds of water, and Mr. Watt's engine, upwards of _thirty millions_ of pounds the same height.

To the mining interests this valuable present of science to the arts has been peculiarly acceptable; as a large portion of our now most productive mineral districts must long ere this have been abandoned, had not the steam-engine been employed as an active auxiliary in those stupendous works. In the draining of fens and marsh lands, this machine is in the highest degree valuable; and in England, particularly, it might be rendered still more generally useful. In practice it has been ascertained that an engine of six-horse power will drain more than eight thousand acres, raising the water six feet in height; whilst the cost of an engine for this species of work, including the pumps, will not exceed seven hundred pounds. This is more than ten windmills could perform, at an annual expenditure of several hundred pounds; while, in the former case, the outgoings will not exceed one hundred and fifty pounds per annum. To the mariner also, the steam-engine offers advantages of a no less important and novel nature than those which have already been described. By its use he is enabled to traverse the waters both against wind and tide, with nearly as much certainty, and, as the machinery is now constructed, with much less danger, than by the most eligible road conveyance. It too frequently, however, happens that the faults of any new invention are unjustly magnified, while its real advantages are seldom duly appreciated; and this axiom has been fully verified, in the clamour so unjustly raised against the application of the steam-engine to nautical purposes. Accidents are now, however, but of rare occurrence; and it is more than probable, that the great improvements which have been made in the boiler and safety-valve will effectually secure these parts of the engine from a recurrence of such tremendous explosions as characterised the first introduction of steam navigation. And, lastly, the political economist must hail with the most heartfelt gratification, the introduction of so able and efficient a substitute for animal labour as the steam-engine. For it has been calculated that there are at least ten thousand of these machines at the present time at work in Great Britain, performing a labour more than equal to that of two hundred thousand horses, which, if fed in the ordinary way, would require above one million acres of land for subsistence; and this is capable of supplying the necessaries of life to more than fifteen hundred thousand human beings.[11]

[11] _Vide_ Historical Account of the Steam-engine, by C. F.
Partington.

An ingenious foreigner, who lately visited England, has published an estimate of the mechanical force set in action by the steam-engines of this country.

He supposes that the _great pyramid_ of Egypt required for its erection the labour of more than 10,000 men for 20 years:--but if it were required again to raise the stones from the quarries, and place them at their present height, the action of the steam-engines of England, which are managed at most by 36,000 men, would be sufficient to produce the same effect in 18 hours.

THE END.

LONDON:
PRINTED BY C. ROWORTH, BELL YARD,
TEMPLE BAR.

* * * * *

Transcriber's note:

Minor typographical and punctuation errors have been corrected without note. Irregularities and inconsistencies in the text have been retained as printed.

The cover for the eBook version of this book was created by the transcriber and is placed in the public domain.

On pages 84 and 85 there are two items both of which are numbered LXXXVIII. The table of contents reflects the same.

In the table of contents the following page numbers have been changed to match the book:

Page lxxxii:
33. A Needle Alphabet--39 changed to 38
38. A Sieve Alphabet--ibid. changed to 41

Page lxxxiv:
79. A total locking of Cabinet Boxes--78 changed to 77
80. Light Pistol Barrels--ibid. changed to 78