James Watt — 09 -- Chapter 7, Part 1

SECOND PATENT

The number and activity of rivals attracted to the steam engine and its possible improvement, some of whom had begun infringements upon the Watt patents, alarmed Messrs. Watt and Boulton so much that they decided Watt should apply for another patent, covering his important improvements since the first.

Accordingly, October 25, 1781, the patent (already referred to on p. 91) was secured, "for certain new methods of producing a continued rotative motion around an axis or centre, and thereby to give motion to the wheels of mills or other machines."

This patent was necessary in consequence of the difficulties experienced in working the steam wheels or rotatory engines described in the first patent of 1769, and by Watt's having been so unfairly anticipated, by Wasborough in the crank motion.

No less than five different methods for rotatory motion are described in the patent, the fifth commonly known as the "sun and planet wheels," of which Watt writes to Boulton, January 3, 1782, I have tried a model of one of my old plans of rotative engines, revived and executed by Mr. Murdoch, which merits being included in the specification as a fifth method; for which purpose I shall send a drawing and description next post.

It has the singular property of going twice round for each stroke of the engine, and may be made to go oftener round, if required, without additional machinery.

Then followed an explanation of the sketch which he sent, and two days later he wrote, "I send you the drawings of the fifth method, and thought to have sent you the description complete, but it was late last night before I finished so far, and to-day have a headache, therefore only send you a rough draft of part."

In all of these Watt recommended that a fly-wheel be used to regulate the motion, but in the specification for the patent of the following year, 1782, his double-acting engine produced a more regular motion and rendered a fly-wheel unnecessary, "so that," he says, "in most of our great manufactories these engines now supply the place of water, wind and horse mills, and instead of carrying the work to the power, the prime agent is placed wherever it is most convenient to the manufacturer."

This marks one of the most important stages in the development of the steam engine.

It was at last the portable machine it remains to-day, and was placed wherever convenient, complete in itself and with the rotative motion adaptable for all manner of work.

The ingenious substitutes Watt had to invent to avoid the obviously perfect crank motion have of course all been discarded, and nothing of these remains except as proofs, where none are needed, that genius has powers in reserve for emergencies; balked in one direction, it hews out another path for itself.

While preparing the specification for this patent of 1781, Watt was busy upon another specification quite as important, which appeared in the following year, 1782. It embraced the following new improvements, the winnowing of numberless ideas and experiments that he had conceived and tested for some years previous: 1. The use of steam on the expansive principle; together with various methods or contrivances (six in number, some of them comprising various modifications), for equalising the expansive power.

2. The double-acting engine; in which steam is admitted to press the piston upward as well as downward; the piston being also aided in its ascent as well as in its descent by a vacuum produced by condensation on the other side.

3. The double-engine; consisting of two engines, primary and secondary, of which the steam-vessels and condensers communicate by pipes and valves, so that they can be worked either independently or in concert; and make their strokes either alternately or both together, as may be required.

4. The employment of a toothed rack and sector, instead of chains, for guiding the piston-rod.

5. A rotative engine, or steam-wheel.

Here we have three of the vital elements required toward the completion of the work: first, steam used expansively; second, the double-acting engine.

It will be remembered that Watt's first engines only took in steam at the bottom of the cylinder, as Newcomen's did, but with this difference: Watt used the steam to perform work which Newcomen could not do, the latter only using steam to force the piston itself upward.

Now came Watt's great step forward.

Having a cylinder closed at the top, while the Newcomen cylinder remained open, it was as easy to admit steam at the top to press the piston down as to admit it at the bottom to press the piston up; also as easy to apply his condenser to the steam above as below, at the moment a vacuum was needed.

All this was ingeniously provided for by numerous devices and covered by the patent.

Third, he went one step farther to the compound engine, consisting of two engines, primary and secondary, working steam expansively independently or in concert, with strokes alternate or simultaneous.

The compound engine was first thought of by Watt about 1767. He laid a large drawing of it on parchment before parliament when soliciting an extension of his first patent.

The reason he did not proceed to construct it was "the difficulty he had encountered in teaching others the construction and use of the single engine, and in overcoming prejudices"; the patent of 1782 was only taken out because he found himself "beset with a host of plagiaries and pirates."

One of the earliest of these double-acting engines was erected at the Albion Mills, London, in 1786. Watt writes: The mention of Albion Mills induces me to say a few words respecting an establishment so unjustly calumniated in its day, and the premature destruction of which, by fire, in 1791, was, not improbably, imputed to design.

So far from being, as misrepresented, a monopoly injurious to the public, it was the means of considerably reducing the price of flour while it continued at work.

The "double-acting" engine was followed by the "compound" engine, of which Watt says: A new compound engine, or method of connecting together the cylinders and condensers of two or more distinct engines, so as to make the steam which has been employed to press on the piston of the first, act expansively upon the piston of the second, etc. , and thus derive an additional power to act either alternately or co-jointly with that of the first cylinder.

We have here, in all substantial respects, the modern engine of to-day.

Two fine improvements have been made since Watt's time: first, the piston-rings of Cartwright, which effectively removed one of Watt's most serious difficulties, the escape of steam, even though the best packing he could devise were used--the chief reason he could not use high-pressure steam.

In our day, the use of this is rapidly extending, as is that of superheated steam.

Packing the piston was an elaborate operation even after Watt's day.

It was not because Watt did not know as well as any of our present experts the advantages of high pressures, that he did not use them, but simply because of the mechanical difficulties then attending their adoption.

He was always in advance of mechanical practicalities rather than behind, and as we have seen, had to retrace his steps, in the case of expansion.

The other improvement is the cross-head of Haswell, an American, a decided advance, giving the piston rod a smooth and straight bed to rest upon and freeing it from all disturbance.

The drop valve is now displacing the slide valve as a better form of excluding or admitting steam.

Watt of course knew nothing of the thermo-dynamic value of high temperature without high pressure, altho fully conversant with the value of pressures.

This had not been even imagined by either philosopher or engineer until discovered by Carnot as late as 1824. Even if he had known about it the mechanical arts in his day were in no condition to permit its use.

Even high pressures were impracticable to any great extent.

It is only during the past few years that turbines and superheating, having long been practically discarded, show encouraging signs of revival.

They give great promise of advancement, the hitherto insuperable difficulties of lubrication and packing having been overcome within the last five years.

Superheating especially promises to yield substantial results as compared with the practice with ordinary engines, but the margin of saving in steam over the best quadruple expansion engine cannot be great.

Lord Kelvin however expects it to be the final contribution of science to the highest possible economy in the steam engine.

In the January (1905) number of "Stevens Institute Indicator," Professor Denton has an instructive resume of recent steam engine economics.

He tells us that Steam Turbines are now being applied to Piston Engines to operate with the latter's exhaust, to effect the same saving as the sulphur dioxide cylinder; and adds that the Turbine is a formidable competitor to the Piston Engine is mainly due to the fact that it more completely realizes the expansive principle enunciated in the infancy of steam history as the fundamental factor of economy by its sagacious founder, the immortal Watt.

Watt's favorite employment in Soho works late in 1783 and early in 1784 was to teach his engine, now become as docile as it was powerful, to work a tilt hammer.

In 1777 he had written Boulton that Wilkinson wants an engine to raise a stamp of 15 cwt.

thirty or forty times in a minute.

I have set Webb to work to try it with the little engine and a stamp-hammer of 60 lbs.

weight.

Many of these _battering rams_ will be wanted if they answer.

The trial was successful.

A new machine to work a 700 lbs.

hammer for Wilkinson was made, and April 27, 1783, Watt writes that it makes from 15 to 50, and even 60, strokes per minute, and works a hammer, raised two feet high, which has struck 300 blows per minute.

The engine was to work two hammers, but was capable of working four of 7 cwt.

each.

He says, with excusable pride, I believe it is a thing never done before, to make a hammer of that weight make 300 blows per minute; and, in fact, it is more a matter to brag of than for any other use, as the rate wanted is from 90 to 100 blows, being as quick as the workmen can manage the iron under it.

This most ingenious application of steam power was included in Watt's next patent of April 28, 1784. It embraced many improvements, mostly, however, now of little consequence, the most celebrated being "parallel motion," of which Watt was prouder than any other of his triumphs.

He writes to his son, November, 1808, twenty-four years after it was invented (1784): Though I am not over anxious after fame, yet I am more proud of the parallel motion than of any other mechanical invention I have ever made.

He wrote Boulton, in June, 1784: I have started a new hare.

I have got a glimpse of a method of causing a piston-rod to move up and down perpendicularly, by only fixing it to a piece of iron upon the beam ...

I think it one of the most ingenious simple pieces of mechanism I have contrived.

October, 1784, he writes: The new central perpendicular motion answers beyond expectation, and does not make the shadow of a noise.

He says: When I saw it in movement, it afforded me all the pleasure of a novelty, as if I had been examining the invention of another.

When beam-engines were universally used for pumping, this parallel motion was of great advantage.

It has been superseded in our day, by improved piston guides and cross-heads, the construction of which in Watt's day was impossible, but no invention has commanded in greater degree the admiration of all who comprehend the principles upon which it acts, or who have witnessed the smoothness, orderly power and "sweet simplicity" of its movements.

Watt's pride in it as his favorite invention in these respects is fully justified.

A detailed specification for a road steam-carriage concludes the claims of this patent, but the idea of railroads, instead of common roads, coming later left the construction of the locomotive to Stephenson.

[1] Watt's last patent bears date June 14, 1785, and was for certain newly improved methods of constructing furnaces or fire-places for heating, boiling, or evaporating of water and other liquids which are applicable to steam engines and other purposes, and also for heating, melting, and smelting of metals and their ores, whereby greater effects are produced from the fuel, and the smoke is in a great measure prevented or consumed.

The principle, "an old one of my own," as Watt says, is in great part acted upon to-day.

So numerous were the improvements made by Watt at various periods, which greatly increased the utility of his engine, it would be in vain to attempt a detailed recital of his endless contrivances, but we may mention as highly important, the throttle-valve, the governor, the steam-gauge and the indicator.

Muirhead says: The throttle-valve is worked directly by the engineer to start or stop the engine, and also to regulate the supply of steam.

Watt describes it as a circular plate of metal, having a spindle fixed across its diameter, the plate being accurately fitted to an aperture in a metal ring of some thickness, through the edgeway of which the spindle is fitted steam-tight, and the ring fixed between the two flanches of the joint of the steam-pipe which is next to the cylinder.

One end of the spindle, which has a square upon it, comes through the ring, and has a spanner fixed upon it, by which it can be turned in either direction.

When the valve is parallel to the outsides of the ring, it shuts the opening nearly perfectly; but when its plane lies at an angle to the ring, it admits more or less steam according to the degree it has opened; consequently the piston is acted upon with more or less force.

Papin preferred gunpowder as a safer source of power than steam, but that was before it had been automatically regulated by the "Governor."

The governor has always been the writer's favorite invention, probably because it was the first he fully understood.

It is an application of the centrifugal principle adapted and mechanically improved.

Two heavy revolving balls swing round an upright rod.

The faster the rod revolves the farther from it the balls swing out.

The slower it turns the closer the balls fall toward it.

By proper attachments the valve openings admitting steam are widened or narrowed accordingly.

Thus the higher speed of the engine, the less steam admitted, the slower the speed the more steam admitted.

Hence any uniform speed desired can be maintained: should the engine be called upon to perform greater service at one moment than another, as in the case of steel rolling mills, speed being checked when the piece of steel enters the rolls, immediately the valves widen, more steam rushes into the engine, and _vice versa_.

Until the governor came regular motion was impossible--steam was an unruly steed.

Arago describes the steam-gauge thus: It is a short glass tube with its lower end immersed in a cistern of mercury, which is placed within an iron box screwed to the boiler steam-pipe, or to some other part communicating freely with the steam, which, pressing on the surface of the mercury in the cistern, raises the mercury in the tube (which is open to the air at the upper end), and its altitude serves to show the elastic power of the steam over that of the atmosphere.

The indicator he thus describes: The barometer being adapted only to ascertain the degree of exhaustion in the condenser where its variations were small, the vibrations of the mercury rendered it very difficult, if not impracticable, to ascertain the state of the exhaustion of the cylinder at the different periods of the stroke of the engine;

it became therefore necessary to contrive an instrument for that purpose that should be less subject to vibration, and should show nearly the degree of exhaustion in the cylinder at all periods.

The following instrument, called the Indicator, is found to answer the end sufficiently.

A cylinder about an inch diameter, and six inches long, exceedingly truly bored, has a solid piston accurately fitted to it, so as to slide easy by the help of some oil; the stem of the piston is guided in the direction of the axis of the cylinder, so that it may not be subject to jam, or cause friction in any part of its motion.

The bottom of this cylinder has a cock and small pipe joined to it which, having a conical end, may be inserted in a hole drilled in the cylinder of the engine near one of the ends, so that, by opening the small cock, a communication may be effected between the inside of the cylinder and the indicator.

The cylinder of the indicator is fastened upon a wooden or metal frame, more than twice its own length; one end of a spiral steel spring, like that of a spring steel-yard, is attached to the upper part of the frame, and the other end of the spring is attached to the upper end of the piston-rod of the indicator.

The spring is made of such a strength, that when the cylinder of the indicator is perfectly exhausted, the pressure of the atmosphere may force its piston down within an inch of its bottom.

An index being fixed to the top of its piston-rod, the point where it stands, when quite exhausted, is marked from an observation of a barometer communicating with the same exhausted vessel, and the scale divided accordingly.

Improvements come in many ways, sometimes after much thought and after many experimental failures.

Sometimes they flash upon clever inventors, but let us remember this is only after they have spent long years studying the problem.

In the case of the steam engine, however, a quite important improvement came very curiously.

Humphrey Potter was a lad employed to turn off and on the stop cocks of a Newcomen engine, a monotonous task, for, at every stroke one had to be turned to let steam into the boiler and another for injecting the cold water to condense it, and this had to be done at the right instant or the engine could not move.

How to relieve himself from the drudgery became the question.

He wished time to play with the other boys whose merriment was often heard at no great distance, and this set him thinking.

Humphrey saw that the beam in its movements might serve to open and shut these stop cocks and he promptly began to attach cords to the cocks and then tied them at the proper points to the beam, so that ascending it pulled one cord and descending the other.

Thus came to us perhaps not the first automatic device, but no doubt the first of its kind that was ever seen there.

The steam engine henceforth was self-attending, providing itself for its own supply of steam and for its condensation with perfect regularity.

It had become in this feature automatic.

The cords of Potter gave place to vertical rods with small pegs which pressed upward or downward as desired.

These have long since been replaced by other devices, but all are only simple modifications of a contrivance devised by the mere lad whose duty it was to turn the stop cocks.

It would be interesting to know the kind of man this precocious boy inventor became, or whether he received suitable reward for his important improvement.

We search in vain; no mention of him is to be found.

Let us, however, do our best to repair the neglect and record that, in the history of the steam engine, Humphrey Potter must ever be honorably associated with famous men as the only famous boy inventor.

In the development of the steam engine, we have one purely accidental discovery.

In the early Newcomen engines, the head of the piston was covered by a sheet of water to fill the spaces between the circular contour of the movable piston and the internal surface of the cylinder, for there were no cylinder-boring tools in those days, and surfaces of cylinders were most irregular.

To the surprise of the engineer, the engine began one day working at greatly increased speed, when it was found that the piston-head had been pierced by accident and that the cold water had passed in small drops into the cylinder and had condensed the steam, thus rapidly making a more perfect vacuum.

From this accidental discovery came the improved plan of injecting a shower of cold water through the cylinder, the strokes of the engine being thus greatly increased.

The year 1783 was one of Watt's most fruitful years of the dozen which may be said to have teemed with his inventions.

His celebrated discovery of the composition of water was published in this year.

The attempts made to deprive him of the honor of making this discovery ended in complete failure.

Sir Humphrey Davy, Henry, Arago, Liebig, and many others of the highest authority acknowledged and established Watt's claims.

The true greatness of the modest Watt was never more finely revealed than in his correspondence and papers published during the controversy.

Watt wrote Dr. Black, April 21st, that he had handed his paper to Dr. Priestley to be read at the Royal Society.

It contained the new idea of water, hitherto considered an element and now discovered to be a compound.

Thus was announced one of the most wonderful discoveries found in the history of science.

It was justly termed the beginning of a new era, the dawn of a new day in physical chemistry, indeed the real foundation for the new system of chemistry, and, according to Dr. Young, "a discovery perhaps of greater importance than any single fact which human ingenuity has ascertained either before or since."

What Newton had done for light Watt was held to have done for water.

Muirfield well says: It is interesting in a high degree to remark that for him who had so fully subdued to the use of man the gigantic power of steam it was also reserved to unfold its compound natural and elemental principles, as if on this subject there were to be nothing which his researches did not touch, nothing which they touched that they did not adorn.

Arago says: In his memoir of the month of April, Priestley added an important circumstance to those resulting from the experiments of his predecessors: he proved that the weight of the water which is deposited upon the sides of the vessel, at the instant of the detonation of the oxygen and hydrogen, is precisely the same as the weights of the two gases.

Watt, to whom Priestley communicated this important result, immediately perceived that proof was here afforded that water was not a simple body.

Writing to his illustrious friend, he asks: What are the products of your experiment?

They are _water_, _light_ and _heat_.

Are we not, thence, authorised to conclude that water is a compound of the two gases, oxygen and hydrogen, deprived of a portion of their latent or elementary heat; that oxygen is water deprived of its hydrogen, but still united to its latent heat and light?

If light be only a modification of heat, or a simple circumstance of its manifestation, or a component part of hydrogen, oxygen gas will be water deprived of its hydrogen, but combined with latent heat.

This passage, so clear, so precise, and logical, is taken from a letter of Watt's, dated April 26, 1783. The letter was communicated by Priestley to several of the scientific men in London, and was transmitted immediately afterward to Sir Joseph Banks, the President of the Royal Society, to be read at one of the meetings of that learned body.

Watt had for many years entertained the opinion that air was a modification of water.

He writes Boulton, December 10, 1782: You may remember that I have often said, that if water could be heated red-hot or something more, it would probably be converted into some kind of air, because steam would in that case have lost all its latent heat, and that it would have been turned solely into sensible heat, and probably a total change of the nature of the fluid would ensue.

A month after he hears of Priestley's experiments, he writes Dr. Black (April 21, 1783) that he "believes he has found out the cause of the conversion of water into air."

A few days later, he writes to Dr. Priestley: In the deflagration of the inflammable and dephlogisticated airs, the airs unite with violence--become red-hot--and, on cooling, totally disappear.

The only fixed matter which remains is _water_; and _water_, _light_, and _heat_, are all the products.

Are we not then authorised to conclude that water is composed of dephlogisticated and inflammable air, or phlogiston, deprived of part of their latent heat; and that dephlogisticated, or pure air, is composed of water deprived of its phlogiston, and united to heat and light; and if light be only a modification of heat, or a component part of phlogiston, then pure air consists of water deprived of its phlogiston and of latent heat?

It appears from the letter to Dr. Black of April 21st, that Mr. Watt had, on that day, written his letter to Dr. Priestley, to be read by him to the Royal Society, but on the 26th he informs Mr. DeLuc, that having observed some inaccuracies of style in that letter, he had removed them, and would send the Doctor a corrected copy in a day or two, which he accordingly did on the 28th; the corrected letter (the same that was afterward embodied verbatim in the letter to Mr. DeLuc, printed in the Philosophical Transactions), being dated April 26th.

In enclosing it, Mr. Watt adds, "As to myself, the more I consider what I have said, I am the more satisfied with it, as I find none of the facts repugnant."

Thus was announced for the first time one of the most wonderful discoveries recorded in the history of science, startling in its novelty and yet so simple.

Watt had divined the import of Priestley's experiment, for he had mastered all knowledge bearing upon the question, but even when this was communicated to Priestley, he could not accept it, and, after making new experiments, he writes Watt, April 29, 1783, "Behold with surprise and indignation the figure of an apparatus that has utterly ruined your beautiful hypothesis," giving a rough sketch with his pen of the apparatus employed.

Mark the promptitude of the master who had deciphered the message which the experimenter himself could not translate.

He immediately writes in reply May 2, 1783: I deny that your experiment ruins my hypothesis.

It is not founded on so brittle a basis as an earthen retort, nor on _its_ converting water into air.

I founded it on the other facts, and was obliged to stretch it a good deal before it would fit this experiment....

I maintain my hypothesis until it shall be shown that the water formed after the explosion of the pure and inflammable airs, has some other origin.

He also writes to Mr. DeLuc on May 18th: I do not see Dr. Priestley's experiment in the same light that he does.

It does not disprove my theory....

My assertion was simply, that air (_i.

e. _, dephlogisticated air, or oxygen, which was also commonly called vital air, pure air, or simple _air_) was water deprived of its phlogiston, and united to heat, which I grounded on the decomposition of air by inflammation with inflammable air, the residuum, or product of which, is only water and heat.

Having, by experiments of his own, fully satisfied himself of the correctness of his theory, in November he prepared a full statement for the Royal Society, having asked the society to withhold his first paper until he could prove it for himself by experiment.

He never doubted its correctness, but some members of the society advised that it had better be supported by facts.