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1844.] THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 91 The materials of which such boilers should be constructed, are as follows— Furnaces, of best Low Moor iron 8 in. thick ; the grate and uptake should be of the same kind and substance. The tube plates are some times made of mixed metal; but we prefer Low Moor iron of § inch gauge. The tubes (if of brass) should they be those made by Alston, which are bare } in. thick, or 12 wire gauge. If made of iron, they should be those of Russell & Co. A difference of opinion exists as to the advantages arising from the use of brass or iron tubes, although practice has hitherto been almost confined to the former ; but it appears likely that a great change will shortly take place in this particular, arising from the injurious effects produced by galvanic action on the iron shell of the boiler, which in many boilers has occurred to an alarming extent. Of course this would be actively obviated by the use of iron tubes, and the advan tage of the one over the other, is solely a commercial question, deter minable by practice only. We think the iron tubes Will be found the best in all respects, especially if means are taken (and they are sim ple) to prevent the accumulation of salt and calcareous deposits. The shell and chimney uptake may be of best Staffordshire iron, 8 in. thick, and 4 in. below, say for 2 ft. up from the bottom, where the decay is generally very rapid. Care should be taken in properly staying every part. FARKYN’S DIRECT ACTION ENGINE. ( With an Engraving, Plate 3.J Sir—I herewith send you a drawing of a Double Cylinder Engine, which I patented in England last year. I have erected an engine, similar to that shown on board, the Iron Boat, Prince Albert, built for the Montreal and Laprairie Ferry. The engraving is a longitudinal section through the engine, showing the method of connecting the cylinders with the air-pump, and trans mitting the power to the main shaft. The novelty of the plan is the way in which the air-pump is worked, securing greater economy of space and fewer moving parts, and consequently less friction—these being the primary objects to be attained by all plans of direct acting engines. The cylinders are 42 inches in diameter, and 5 feet stroke. The air-pump is 28 inches, and the same stroke. The plunger of the air-pump is worked down to within 3 in. of the flooring of the vessel, thus securing the longest possible stroke for a given height, with an adequate length of connecting rod, which in the engine shown is ten feet. F, F, are the two foot valves—the discharge is at the side. The two valves G, G, in the air-pump plunger are to allow for the exit of any air that may collect in the pump. The valves of the engine are four in number, two for the steam on the left, and two for the exhaust on the right they are of the kind generally denominated the Equilibrium Valve, and worked by two eccentrics, one for each pair; this is adopted to secure the means of cutting off the steam valve at any part of the stroke. The engine can be started, stopped and handled by a force not exceeding 401b. ap plied to a lever 3 feet long. The condenser is immediately below the nozzles, thus securing instant condensation. The engine at ordinary working makes 21 revolutions with a pres sure of steam of 18 lb. per square inch in the boiler, and cutting off at half stroke, driving a wheel 2G ft. 6 in. diameter, 7 feet wide with 20 inches of dip. The vacuum in condenser averages 284 inches as indicated by the barometer. The boat is 178 feet long between the perpendiculars, 175 feet on keel, 25 feet beam, depth of hold 8 feet, and 2 ft. 9 in. draught of water when light. The boilers are upon the tubular principle, and con structed to burn wood fuel. The boat before the navigation closed was 23 days upon her station, and seemed to answer all the purposes for which she was built. I thus submit to the criticism of English engineers the first Double Cylinder Engine that has been manufactured in Canada, and erected on board the first iron boat built in the colony. I am, Sir, your obedient servant, William Parkyn, St. Mary's Foundry, Montreal, Dec. 12, 1843. P.S. In such class of vessel as the Helen Macgregor, described in the Journal for November, an engine on the plan here submitted could be got in the same space, having a 0 feet stroke and 12 feet connecting rod. [It is very evident that Mr. Parkyn’s engine is a copy of the double cylinder engines of Messrs. Maudslay & Co.; this engine being in every respect, but one, exactly similar to that patented by Joseph Maudslay and Joshua Field on the 7th of May, 1839, and de scribed in the Journal, p. 73, Vol. Ill, 1840. The only novelty, is in placing the air-pump between the cylinders, and making it the guide for the bottom end of the connecting rod; the air-pump is therefore necessarily open topped, and working under the pressure of the at mosphere. This arrangement most undoubtedly reduces this kind of engine to a minimum of space per horse power, and admits of a longer connecting rod than Messrs. Maudslay and Field’s engine, for the reasons given by Mr. Parkyn—his working the air-pump piston to within an inch or two of the vessel’s bottom. There is considerable ingenuity in the scheme, although, if our memory serves us rightly, we have seen it before printed and described in some work, but which we cannot refer to just now. It possesses all the faults of Maudslay’s engines, and which we think have been urged against them with much reason—namely, greatly unbalanced weight, and consequent irregu larity of motion, and perhaps of more consequence still—the surety of a difference in the friction of the two pistons, throwing a heavy strain, and wear and tear onjthe piston rods and working parts con nected therewith. Mr. Parkyn’s engine possesses all these disadvantages, to which must be added his open topped air-pump, which adds to, instead of reducing the unbalanced weight—for he has to bring up the bucket or plunger against the atmosphere, which in a pump of 28 in. diame ter, is equal to four tons or close upon half the power of one cylinder (vacuum pressure.) As the condensation water is, under ordinary working, about equal to one fourth of the air-pump’s content per stroke, it follows that the power requisite for its expulsion into the hot well is exerted only during the last quarter of its descent, and until it reaches that point it is totally inefficient as a balance to the working parts, and then it has become useless from their accelerated motion. Messrs. Maudslay avoid this, although they increase their weight and space, by placing the air-pump as shown in the drawing before referred to (Vol. III., 1840.) There is still another objection to Mr. Parkyn’s plan. The velocity of the air-pump plunger is double that generally given, it is necessa rily the same as the piston, instead of a moiety, and this would be a serious objection in the minds of many English engineers. In the case of a bucket with valves, we should agree as to its impracticability, but we do not think the objection applies with so much force when a solid plunger is used, (as by Mr. Parkyn,) and the delivery valves are made of sufficient capacity. We know of several good engines, that have the strokes of their cylinders and air-pumps equal, the Prince Albert, of London, for instance, just occurs to us. The friction is, of course, greater, in the ratio of 2 to 3, and probably the wear of the air-pump would be considerable, from the oblique action of the con necting rod: but these are matters for practice to determine, and we shall be glad to hear again from Mr. Parkyn, after his engines have been at work for some time, and perhaps he can then favour us with some indicator diagrams taken from the cylinder and from the under side of the air-pump plunger—these would assist our judgment mate rially, and be very interesting. The steam and eduction valves, used by Mr. Parkyn, are those of the Cornish engines—generally known by the name of double beat valves; two sets of eccentrics are applied, and the expansion of the steam is effected by a slot in the eccentric notch, which can be al tered at pleasure, and is both novel, simple and effective: but it is riot applicable to slide valves. On the whole it is a creditable production, although, as we have said before, it is a decided infringement of Maudslay’s patent, in so far as the employment of two cylinders, piston-rods, T piece, &c., is con cerned. However, we cannot help again expressing our pleasure at these liberal exchanges of practical knowledge, between the new and old world, and feel gratified at our Journal being the means of com municating them to the public.]—Editor C. E. & A. Journal. Railways.—First Report from the Select Committee.—The Select Committee appointed to consider whether any what new provisions ought to be introduced into such railway bills as may come before this House during the present or future sessions, for the advantage of the public and the improvement ef the railway system, and likewise to con sider Whether any and what changes ought to be made in the standing orders relating to railways, and who were empowered, to report their opinion thereupon from time to time to the House, have considered the matter referred to them, and have agreed to the fol lowing clause be inserted in all the railway bills now coming before or passing through Parliament, viz., “And be it further enacted, that nothing herein contained shall be deemed or construed to exempt the railway by this or the suid recited acts authorized to be made from the provisions of any general act relating to such bills which may pass during the present session of Parliament* or of any general act relating to railways which may pass during the present or any future session gf Parliament.”