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DESIGN FOR AN UNIFORM ARRANGEMENT OF PERKINS'S HIGHPRESSURE AND SAFETY-ENGINE. BY MR. C. DAVY.

[Mr. Perkins's Steam-Engine speculations, which, a few years ago, excited so much public expectation, have been brought anew into notice by advertisements in the

news

papers, announcing that Mr. P. is now prepared to furnish engines of universal application, which may be worked with a saving of fifty per cent. in fuel, and possess, besides, the incalculable advantage of perfect safety.

The announcement is such, as to have led many persons to infer that Mr. P. has, at length, succeeded in realizing the project which he originally submitted to the public, as the same is described in our First Volume, pp. 36, 81; and more fully explained by several subsequent papers, pp. 123, 152, 170, 204, 226, Vol. I.; and pp. 178, 194, 211, 229, Vol. II. We believe, however, that this is not precisely the fact. The chief novelty for which Mr. P. formerly claimed credit, was the generation of steam from water, confined by mechanical pressure within a strong cylinder till it became so hot, that a drop of it, on being forcibly ejected, would instantly flash into steam. But now Mr. P. injects the water, while cold, into a series of small tubes, enclosed within a furnace, and heated as much as possible; from which tubes it is transmitted, in the shape of steam, to the working cylinder. It would appear, therefore, that Mr. P. has now abandoned all hope of realizing a working engine ou his original plan, and has betaken himself to a mode of construction in which he has the misfortune to be preceded by several not unsuccessful competitors. Eve's engine, described in our Sixth Volume, pp. 331-344, and Babcock's, of which we gave an account in our last Number, and which was successfully applied in America to the propulsion of boats about a year ago, are both, like this of Mr. Perkins, on the tubular plan; so also are those of M'Kirdy and Gurney,

which have been the subject of recent patents. On the merits of Mr. P.'s plan, as compared with these, we pronounce no opinion; if it will only work as well, however, as the following design of our intelligent correspondent, Mr. Davy, will make it look well, it can have little to fear from competition.-EDIT.]

Sir,

For the purpose of illustrating the conclusion of the subject upon which I have been treating (the Proportions of Steam Engines), I now send you a design for an uniform arrangement of the celebrated high-pressure and safety-engine of Mr. Jacob Perkins. Owing to peculiar local circumstances, Mr. Perkins found it necessary, in the construction of his original engine (a single acting one), to place his steam generators under the engine, and consequently was obliged to introduce two very awkward-looking pipes for its transmission to the working cylinder. To make the design of this engine appear somewhat classical (a study which it is well worthy of), I have, in the present design for the front elevation of the engine, erected the cylinder upon a stand, supported by four columns and entablature complete of the Roman Doric order. This stand I have kept of the same height as that of his present engine, namely, 5 feet 8 inches from the floor to the top of the entablature.

The valve A is for the admission of steam to the cylinder, at a pressure of 800 lbs. upon the square inch! By the action of a lever and eccentric, the rod C is pressed upwards, and draws the cock D downwards, which admits the steam for one-eighth part of the stroke, when it expands, and drives the piston downwards. The fly-wheel returns the piston to its place. The throttle valve is placed at B, making au uniform arrangement with the steam valve A. The rod E, from the governor, continues in a horizontal position to F; and then passes downwards, and is attached at G. We suppose, in the present instance, that the steam generators are on a level floor with the engine. The

Do. do. piston, 8 inches.

Do. do. connecting rod, 3 inches. Length of do. 3 feet 7 inches. Diam. of piston-rod, 24 inches full. Do. of steam-pipes made of copper, L H I, 1 inches full.

Stroke of the engine, 1 foot 8 in. Difference between induction-pipe L and escape-pipe M is as 1 to 200.

By the application of the engine to boats, if on a lee-shore, Mr. P. can convert two 15-horse engines into 60 of power, by using double the quantity of coals.

Mr. P. is erecting an engine on this plan at St. Catherine's Docks, now building, when the public will shortly be satisfied as to the precise extent of its power and economy. I remain, Sir,

Your's respectfully,

CHRIS. DAVY, Teacher of Architecture, Perspective, &c. L. M. Í. and 11, Furnival's Inn.

Mr. Dary's attention having been chiefly directed to Mr. Perkins's engine, with a view to its relative proportions, he has not, we fear, described, with the minuteness necessary to complete information on the subject, the mode in which the steam is generated; and in which, we presume, the principal merit of the engine must consist: we therefore add a few particulars. P.'s steam generators consist of three tiers of cast-iron tubes, five inches square, and 14 inches internal diameter, and laid horizontally in the furnace. The tubes of the first and second tiers communicate with each other in front and rear, forming, as it were, one continned tube.

Mr.

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The water is injected through this double series of tubes by a forcingpump connected to, and worked by, the engine; and discharged from them, at every stroke of the engine, into the third, or lowest, and hottest tier of tubes (which also communicate with each other), where, we are told, it "instantly flashes into steam;" and from which, at all events, it is transmitted, in the form of steam, to a receiver or steamchamber, by which the working cylinder is supplied. The steam, after having performed its office, is partly condensed (by a jet of cold water), and returned to the forcing-pump, and partly conveyed away by the flue of the furnace.-EDIT.

388

99

70=1.4143.

m 99, n = 70; since In order to find these exact values, I have seen no other direction than that of setting the rule as exactly as possible according to the original numbers, and noting those actual divisions which appear to coincide. This method is, however, very unsatisfactory; as the result is affected both by an inaccuracy in the setting, and by the unavoidable errors of graduation. Indeed, many writers on the subject seem entirely ignorant of the principle itself.

Mr. Goodwyn's "First Centenary, and Tabular Series of Decimal Quotients," will enable us to find. out the most accurate integral numbers; and, in most cases, will give them by mere inspection.

such exist. Thus, by the Table of Areas, at the end of Dr. Gregory's Mathematics, the diameter being 7.4, the area is 43.0084. Take m 43, and we have 7.42: 43:1 ;0-785245, an approximation twice as near as the former one.

Now, the superficies of a sphere is four times the area of its great circle; therefore, for the diameters and surfaces of spheres, we have n = 74, m = 4 x 43 172. Mr. Bevan's numbers for the area are 490 and

24, which vary considerably from the truth; and, for the superficies, he has not attempted any exact value.

When the method by Goodwyn's Table gives too high a value for m on the line C, and there is no special Table to be consulted, we must proceed by trial and error.

Now, when the slide is inverted, the square of any number on D, multiplied by its corresponding number on the slide, will always be the same, In the present instance, the constant product should be 353-036, being the cylindrical inches in a gallon. Applying this rule to the pairs of numbers just noted, the results are as stated above; whence it is easy to see that m 21, n=4·1. The numbers of the second pair are those adopted in my 17th formula, in the volume already referred to; but either of them is sufficiently exact in practice.

6. My illustrations of the sliding rule have far exceeded the bounds originally proposed. I trust, however, that they will be considered, by those who peruse them with attention, as confirming the truth of the motto prefixed to my second paper.

Before concluding, I may be allowed to add a few observations. It appears, upon inquiry, that the double slide carpenter's rule is not usually made for sale; but there is a two-feet single slide rule, called the engineer's rule, having the D line commencing with 1, and having on the lower part of the same surface a table of divisors for weights and measures, with some others. These rules may be had of Coulsell, Castle Street, Borough, at 5s. 6d. I cannot say that the numbers put upon this rule are by any means the most useful for mechanics, or even for engineers: however, the maker will insert any other table (containing no greater number of figures) at the same price, if a pattern be furnished him; and should it appear from any communications to this Magazine, that the mechanics wish to have a rule of a more suitable description, I shall be happy to furnish the maker with such a set of fixed numbers, as, in my judgment, is most appropriate and convenient for them.

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Strength of Timber. In all 155 formulæ. Having a few copies to spare, I have deposited them with Mr. Elliott, Mathematical Instrument Maker, Great Newport Street, St. Martin's Lane, to whom persons wishing for copies may apply.

7. At the end of Mr. Bevan's Treatise, is an extensive Table of Divisors and Gauge Points, for the weight of 45 substances; but he has not given the specific gravities assumed in the construction of the Table, nor the formula for computing the numbers for other substances. The latter omission I shall here supply.

Sliding Rule," for the use of the

Mechanics' Institutions in, this part

• Twelve shillings, and six shillings for the Treatise.

12 s

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3 sp 4 a

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288 s p

6 a

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3 sp 4 a

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