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AIR ENGINE COMPANY. 
 
 INCORPORATED UNDER THE LAWS OF THE STATE OF NEW HAMPSHIRE. 
 
 CAPITAL STOCK, $1,000,000. 
 
 10,000 SHARES. 
 
 2000 SHARES PREEERRED STOCK. 
 8000 SHARES COMMON STOCK. 
 
 DIRECTORS. 
 
 JAMES A. WOODBURY. JOSHUA MERRILL. GEORGE PATTEN. 
 E. FRANK. WOODBURY. GEORGE A. KEELER. 
 
 JAMES A. IVOODBURY, President. HIRAM M. GOODRICH, Clerk. 
 
 JOSHUA MERRILL, Treasurer. E. FRANK. WOOIIBURV, Constmcting Engineer. 
 
 Counsel for tloe Compeiny. 
 CH.\RI.ES C. MORG.AN, 32 Pemberton Square, Boston. 
 
 OEEICES. 
 
 No. 2 Goodrich Block, | No. 8 Exchange Place, 
 
 NASHUA, N. H. BOSTON, MASS. 
 
Digitized by the Internet Archive 
 in 2017 with funding from 
 Columbia University Libraries 
 
 https://archive.org/details/treatiseOOwood 
 
Kxgine 
 
 Cox'ererl by aii( l Eipplicatic )iis f( )r F*£iteot«, 
 
 iiT^ tbe LJiiitecl St/ites, Ca.iiacla, and Ktirope. 
 
 PATENTS GRANTED BY THE UNITED STATES OF AMERICA. 
 
 Xo. 
 
 228712. 
 
 Dated 
 
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X REATISE. 
 
 In submitting this treatise we trust that the presentation of this subject 
 will command the attention of all users of motive power. 
 
 Appended to the treatise will be found a series of illustrations ; the testi- 
 monials of the firm of Messrs. Hancock & Allen, who have used one of our 
 experimental engines in the driving of their works at Winchendon, Mass., for 
 five years ; the Expert Report of George H. Barrus, relative to a 35 Horse 
 Power Engine on exhibition at the works of the Downer Kerosene Oil Co., at 
 South Boston ; the opinions of several Engineers as to the value of the Engine ; 
 and quotations from various authorities, with explanatory notes. 
 
 Any information concerning our engine, we will with pleasure impart. 
 
 James A. Woodbury. 
 
 Joshua Merrill. 
 
 Inventors. 
 
 George Patten. 
 
 Edward F. Woodbury. 
 
 Boston, 1889. 
 
Superiority of the Engine. 
 
 Tlic essential features of our engine are a heater, regenerator, and cooler, which three 
 in combination are termed a reverser. The engine illustrated is com])o.sed of two reversers 
 and two double acting working cylinders. It is not an e.xhausting engine, therefore, it has 
 
 neither admission nor exhaust valves. It is claimed to be the best motor ever produced, 
 for the following reasons: — 
 
 It is absolutely safe. 
 
 It is simple in construction. 
 
 It is noiseless in operation. 
 
 It is durable and well arranged in all its parts. 
 
 It is constant in its speed. 
 
 It is made from improved designs and new patterns. 
 
 It is made of the best materials, in the most workmanlike manner. 
 
 It is economical in its operation, requiring one-half less fuel than any other engine. 
 
 It is interchangeable in all its wearing or working parts, therefore, duplicate parts can 
 
 be immediately supplied. 
 
 It is perfectly lubricated at less expense than any other engine, requires the minimum 
 
 amount of attention, it occupies less room, and it costs no more than a steam, gas, or any 
 other style of engine plant of the same power and workmanship. 
 
 The expense to the inventors in working up the engine to its present perfected state, 
 has been the expenditure of Si 50,000. in cash, and twelve years of their time. It may be 
 
 projierly stated at this time, that our action in delaying the introduction of our engine has 
 
 been the subject of criticism ; but, it has been deemed advisable by us, though at great 
 
 personal present loss and discomfort to perfect the engine at our expense, rather than at the 
 
 expense of the public. The engines made by us to-day are more than twice as practical, 
 
 durable, and economical as the engines made six years ago, nevertheless, the engine sold to 
 Ozro Hancock, ICsq., made about six years ago, has given him and his successors, IMessrs. 
 
 Hancock & Allen, the greatest of .satisfaction during a run of five years. See appended 
 
 testimonial. 
 
 CONSTRUCTION. 
 
 The illustrations, represent our 35 Horse Power Ifngine. P'igure i is an elevation, 
 
 figure 2 is a plan, and figure 3 is a vertical sectional view of one reverser and working 
 
 cylinder. The reversers are in duplicate, so also are the working cylinders. 
 
 Plach reverser is provided with a reverser heater, placed within a furnace ; a regenerator, 
 composed of wire cloth of great superficial area, extending from the cooler to the bottom 
 
 of the reverser heater ; a cooler, composed of a large number of thin copper tubes, which 
 
 are surrounded by water ; and a displacer piston, having metallic jiacking rings, and adapted 
 
 to reciprocate within the cooler. Each working cylinder is provided with a working piston 
 
 having metallic packing rings. Each reverser is connected by means of pipes with the working 
 
cylinders, as follows : — The hot chamber below the displacer piston is connected with the 
 bottom of the working cylinder directly opposite ; and the cold chamber above the displacer 
 piston is connected with the top of the working cylinder diagonally opposite. 
 
 The means employed of converting the reciprocating motion of the pistons into a rotating 
 motion are all of a common type. 
 
 A small single acting air pump, having a leather packed piston, is operated by an eccentric 
 fastened to the main shaft. This pump is used, first ; to compress the air to the initial pressure 
 required, second ; to maintain the initial pressure so attained, which is subjected to loss bv 
 leakage around the piston rods, which are packed in a very cheap, durable, and efficient manner, 
 by means of cup-shaped leather packings. 
 
 The regulation of the speed of the engine is obtained by a balanced equalizing valve of 
 simple construction, placed in an equalizing pipe which connects the top of the working cylinders 
 together. The valve being operated by a common centrifugal governor. 
 
 OPERATION. 
 
 The power produced is due to the energy exerted upon the working pistons, by the alternate 
 raising and lowering of the temperature of the same mass of air within the reversers. 
 
 When sufficient heat has been imparted to the reverser heaters, by the combustion of any 
 kind of fuel within the reverser furnaces, the engine may be started by the use of compressed 
 air (previously compressed into a small reservoir) admitted into the engine in an alternate manner, 
 similar to the starting of a Corliss engine, by means of starting valves, (two common lever or 
 globe valves). This method of starting is employed in engines of large sizes, or when it is 
 desired to start an engine under a load. Engines of small sizes may be started as above, or by 
 the use of a starting lever applied to the rim of the fly wheel, or by giving the fly wheel a 
 one-half turn. 
 
 The cooling medium used is any kind of water, or a blast of air circulated through the 
 coolers. A very small quantity of water is required, and the same body of water may be used 
 over and over again. 
 
 DETAILED DESCRIPTION OF OPERATION. 
 
 In the operation, the alternate raising and lowering of the temperature of the same mass 
 of air is accomplished as follows: — In the upward stroke of the displacer piston, the mass of air 
 in the cold chamber above the piston is forced. Frst, through the cooling tubes, in its downward 
 passage, through which the temperature of the air is not materially changed. Second, the air 
 enters the regenerator, and in its passage through the same it absorbs heat which has been 
 imparted to the regenerator. Third, the air then passing over the heated surface of the reverser 
 heater, thereby becoming further heated, enters the hot chamber Ijelow the displacer piston. 
 
 The temperature of the air in the cold chamber is about 120° F., and the temperature of 
 the air in the hot chamber is about 600° F. 
 
 In the downward stroke of the displacer piston, the mass of air is forced. First, to the 
 regenerator. Second, the air enters the regenerator, and in its passage through the same, it 
 deposits thereon the greater portion of its heat. Third, through the cooling tubes, where its 
 
tcm[)crature is rctluced to aliout 120° I'., and tlion into the cold chainl^cr above tlie disiilacer 
 piston. Therefore, at each upward and downward stroke of the displacer ])islon. the temperature 
 of the same mass of air is alternately raised and lowered. The reversers bein;;' in duplicate, it 
 is obvious that the same alternate raising and lowering of the temperature of the displaced air 
 would take place in one reverser as in the other; but, at o])posite times; that is to sav, both 
 displacer pistons being ojierated b)' the reverser beam, whenever one displacer piston is making 
 its upward stroke, the other displacer jiiston is making its downward stroke. It is therefore 
 evident, that when the disj^laced air in one reverser is being heated, the disjilacetl air in the other 
 reverser is being cooled. 
 
 The alternate raising and lowering of the temperature of the displaced air, (in both re- 
 versers) generates a jiower in accordance with the well-known laws of the e.xpansion of gases, 
 which iiower is developed by the working cylinders, as follows; — While one displacer piston is 
 making its upward stroke, and is heating and exi)anding the displaced air, thereby producing a 
 pressure which is exerted against the bottom of the working piston of the working cylinder 
 directly oj^posite the reverser, and against the top of the working piston of the working cylimler 
 diagonally opposite ; the other displacer piston is making its downward stroke, and is cooling and 
 contracting the displaced air, thereby reducing the pressure against the bottom of the working 
 piston, of the working cylinder directly opposite the reverser, and the top of working piston of 
 the working cylinder diagonally opposite. Thus each working piston is subjected to differential 
 pressures, which are alternately reversed as the displaced air is alternatelv heated and cooled. 
 Thus a power is exerted to cause the working pistons to have a reciprocating motion, which is 
 changed to a rotary motion by means of the working cylinder beam and its connected parts to 
 the main shaft and the fly wheel, from which the power may be taken off b}' a belt. A por- 
 tion of the power developed is absorbed in the friction of the engine, and a portion is used to 
 operate the displacer pistons, by means of a reverser crank, reverser connecting rod, side lever, 
 trunnion, reverser beam, and connected parts. The engine is designed to run on an initial 
 pressure (per gauge) of air of about forty-five pounds, at a speed of 115 revolutions j^er minute. 
 
 At each revolution of the engine the cpiantity of air (compressed) required to siqoply the 
 initial pressure and leakage is pumped, preferably, into a reservoir, from which the air passes 
 through check valves (one check valve for each working cylinder) into the engine, and a lever 
 safety valve is attached to the reservoir as a means of controlling the initial pressure of the 
 air used. 
 
 SPECIAL ADVANTAGES DUE TO CONSTRUCTION. 
 
 The working pistons being connected by means of a beam, are therefore counterbalanced. 
 The displacer pistons are counterbalanced in a like manner. The temperature of the surfaces 
 against which the metallic i)acking rings of the displacer pistons slide, is about 90'^ I'., and the 
 temperature of the surfaces against which the metallic packing rings of the working jnstons slide, 
 is about 180° F. All the pistons operating in vertical lines wear the cxlinders evenly, and by 
 reason of their vertical positions they require the minimum amount of set to the packing rings, 
 and the consequent friction of the pistons is reduced to the smallest amount possible. There- 
 fore, for the reasons above given, and also that there is no exhaust, the amount of oil required 
 to lubricate the pistons is reduced to a minimum quantity. 
 
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FIGURE 2. 
 

FIGURE 3. 
 
Air Hngine Xest. 
 
 By Geo. H. Barrus, M. E. 
 
 Mr. JOSHUA MERRILL, Treasurer, 
 
 OF THE 
 
 Woodbury, Merrill, Patten, & Woodbury Air Eugiue Co., 
 
 8 Exchange Place, Boston, Mass. 
 
 Dear Sir ; 
 
 Having made at your request a series of tests on the No. 13 Woodbury, Merrill, 
 Patten, & Woodbury Air Engine, at your works in South Boston, the object of which 
 was to determine the economy as to consumption of fuel with which the engine works, I 
 beg to submit the following table, a brief summary of the principal results of the same. 
 A description of the engine, and the method of conducting the tests, together with a full 
 record of the results, is given in a detailed report, which I will submit at an early day. 
 
 On all the tests except the last, the principal load on the engine, consisted of a 
 No. 35 Sturtevant Exhausting P’an, with 72 inch case, which makes 535 revolutions per 
 minute when the engine makes iio revolutions per minute. On the last test, the principal 
 load consisted of the same fan, and in addition, a Sturtevant P'an, with 60 inch case, No- 
 123, which made about 625 revolutions per minute. The friction of the engine was deter- 
 mined by subtracting the average power absorbed by a Prony Brake, applied to the fi}'-wheel, 
 from the indicated Horse Power developed at the same time, on the occasion of supplementary 
 tests, a part of which were made March 7th, and a part, March 22nd, the number of these 
 tests being fourteen. The average Indicated Horse Power was 31.18, and the average Brake 
 Horse Power, 19.92 
 
 It appears from the table, taking the test of March 23rd as a proper indication of 
 the performance of the engine, that the amount of coke used in a ten hours run, including 
 
 the wood and coke required to start the fire, beginning with a cold engine, was 1.91 lbs. 
 
 per Indicated Horse Power per hour, and 2.98 lbs. per Brake Horse Power per hour. On 
 
 the same test, for a period of hours, after the engine had attained its normal conditions 
 
 of work, the quantity of coke consumed was 1.54 lbs. per indicated Horse Power per hour, 
 and 2.37 lbs. per Brake Horse Power per hour. During the test of 'March 6th, the quantity 
 of water which passed through the Coolers amounted to an average of 3612 lbs. per hour, 
 which is equivalent to 7.2 gallons per minute. This water was supplied at a temperature 
 of 36 degrees, and discharged at a temperature of 102.8 degrees. 
 
I do not regard these results as the best that can be obtained from the engine, for 
 there is a consideral)le loss of heat from the unprotected exterior surfaces of the Furnaces, 
 due to radiation, which can easily be prevented by the use of suitable covering. 
 
 Taking the results as they stand, however, the consumption of fuel per Effective Horse 
 Power transmitted through the belt, is not more than one-half of that required for the best 
 non condensing steam engines of small power, which are commonly used. 
 
 It appears to me that the engine, in its present shape, may be successfully placed on 
 
 the market, with the assurance of satisfactory results in practical operation, and I believe 
 
 that its economy in the consumption of fuel and entire safety will commend it to any 
 person requiring motive power. 
 
 In view of the very large improvement that has already been made in the econom}' of 
 the engine, and in view of the evident losses which have been referred to, which are still going 
 on, it seems quite probable that an engine of this type can be made which will develop an indi- 
 cated Horse Power on a consumption of i lb. of coal per hour ; measuring the coal during a 
 period beginning with the fires in a normal condition, and ending with the fires in the same 
 condition. This is one-third less than the results of the test of March 23d, giving 1.5 lbs. of 
 coal per indicated Horse Power per hour. 
 
 I am, P^aithfully yours, 
 
 GEO. H. BARRUS, 
 
 E.xpert and Consulting Steam Engineer, 
 
 March 29, 1S89. 
 
 No. 95 Milk St., Boston. 
 
I. KIND OF FUEL. 
 
 
 *'G.\.S HOUSE COKE. 
 
 
 ( iLori.i '.s ('leek 
 Cuiiiberliiiui 
 ( 'o:il. 
 
 2 
 
 1 )ate of Test. i S89. 
 
 Mar. 5. 
 
 Mar. 6. 
 
 Mar. 23. 
 
 Mar. 23. 
 
 -Mar. 25. 
 
 n 
 
 0 - 
 
 Duration .... hrs. 
 
 7 - 
 
 8.25 
 
 10. 
 
 6.25 
 
 5 - 
 
 4. 
 
 Condition of fire at 
 beoinnino- and end. 
 
 0 0 
 
 Normal. 
 
 liegin with New 
 Fire. 
 
 Find with Fire 
 burned out. 
 
 Kegin with New 
 Fire. 
 
 End with Fire 
 burned out. 
 
 Normal. 
 
 Normal. 
 
 5 - 
 
 Weight of dry fuel 
 burned, including 4-10 
 of weight of wood 
 used for lighting fire 
 lbs. 
 
 342. 
 
 453-6 
 
 601.6 
 
 314- 
 
 262. 
 
 6. 
 
 Weight of dry fuel 
 burned per hour lbs. 
 
 48.9 
 
 55 - 
 
 60.2 
 
 50. 
 
 52-5 
 
 7 - 
 
 Indicated H. P. devel- 
 oped by engine, I.H.P. 
 
 30.16 
 
 29.68 
 
 31-45 
 
 32-38 
 
 32.43 
 
 8. 
 
 Revolutions per min. 
 
 113-1 
 
 1 1 2.4 
 
 1 1 2.5 
 
 113-6 
 
 108.4 
 
 9 - 
 
 P'uel burned per I.H.P. 
 per hour lbs. I 
 
 1.62 
 
 1.85 
 
 1.91 
 
 1-54 
 
 i 1 
 
 1 
 
 1.62 
 
 10. 
 
 P'uel burned per Brake 
 H.P. per hour, assum- 
 ing friction of 11.26 
 HA\ 
 
 2-59 
 
 2-99 
 
 2.98 
 
 2-37 
 
 1 
 
 i 2.48 
 
 * 0 n the test of INIarch 5th, the coke when fired, contained 20% of moisture, and on 
 that of March 6th, 14.2% of moisture, determined by drying samples. 
 
 On the test of March 23rd, the coke when fired, was dry. 
 
Testimonials. 
 
 Established 1S45. 
 
 HANCOCK cN ALLEN, 
 
 Successors to Ozro Hancock, 
 
 Mr. Josht-A Merrill, Treasurer, Winxhexdox, Mass., March 5th, 1889. 
 
 Woodbury, Merrill, Patten & Woodbury Air Engine Co., 
 
 8 E.xchange Place, Boston, Mass. 
 
 Dear Sir, — Having for the past five years used one of your Air Engines, I gladly certify that 
 it has proved most e.xcellent, in every respect, as a motor. The consumption of fuel has never exceeded 
 350 lbs. per day, including the starting fires. The engine requiring very little attention, the engineer 
 being able to do at least three-quarters of a day's work at tools, besides caring for the engine. The 
 power being steady and uniform, no apprehension of danger to trouble us, and, in short, I consider it 
 a most valuable and reliable motor. Since putting in our new engine of an improved make, we are 
 using 2^0 lbs. only of bituminous coal, with a small amount of spent tan bark in combination. This 
 includes the starting coal, or the entire consumption for the day, the engine indicating about 14 Horse 
 Power, and, to drive our entire machinery, requiring at least 10 delivered Horse Power. The engine 
 runs beautifully; steady motion; regulates as closely as the best steam engine, and is most satisfactory 
 in every particular. I feel you will have great success in the sale of this engine to all people requiring 
 power, and I wish you the success so hne an invention is worthy of. 
 
 I am, respectfully yours, 
 
 JoHX Haxcock, 
 
 Of the firm of Hancock & Allen. 
 
 Mr. Joshua Merrill, Treasurer, 31 Milk Street. Boston’, April 6, 1889. 
 
 Woodbury, Merrill, Patten &: Woodbury Air Engine Co., 
 
 8 Exchange Place, Boston, Mass. 
 
 Dear Sir, — In reply to your inquiry, I have seen the various air engines invented by yourself 
 and associates, and have taken note of the continued improvements added from time to time for several 
 years, and therefore am able to express my confidence in their practical operation, safety from explo- 
 sions, and economy in fuel. 
 
 Yours very truly, C. J. H. Woodbury 
 
 M. C. Bullock, Pres. Geo. Woodland, Treas. O. H. Blanke, Sec'y. J. S. Lane, Gen'l Supt, 
 
 M. C. BULLOCK MANF’G CO., 
 
 Phenix Huilding, No. 138 Jackson Strcef. 
 
 Works : Lake St. and Talman Avenue. 
 
 Mr. Joshua Merrill, Treasurer, Chicago, U. S. A., April 15, 1889. 
 
 Woodbury, Merrill, Patten N: Woodbury Air Engine Co., 
 
 8 BLxchange Place, Boston, Mass. 
 
 Dear Sir, — Replying to your favor of the iith, I beg to acknowledge, not only your very kind 
 letter, but also the report of the tests made by Geo. H. Barrus, on the Woodbury, Merrill, Patten &: 
 Woodbury Air Engine. 1 have examined the tests very carefully, and am more than pleased with the 
 results, and I wish to congratulate you most heartily upon the advance which you have made in 
 perfecting this remarkable engineering problem. 
 
 With kind regards, and wishing you the success which you so richly deserve, I am. 
 
 Yours very sincerely, M. C. Bullock, Frcs't. 
 
I). M WrsTuN, Pr^s. W’m. ( ). LiNcoi.N. Treats. Hhnj. 1- . Rai>foki>, Gfn. 
 
 ■J’HE AMERICAN 'I'OOI. N: MAC'HINE CO.. 
 
 Kingston Street, 
 
 Mr. Joshu.v Merrill, ' Irtasurcr . Uu.sidn. M.\s.s., April 25, 18S9. 
 
 Woodbury, Merrill, Ratten N Woodbury Air Engine Co., 
 
 8 Exchange Rlace, Roston, .Mass. 
 
 1 )e.\r Sir, — Ha\'ing carefully read the report, by Mr. Rarrus, of se\'eral trials of }'our engine, 
 made for the purpose of ascertaining its economy in the consumption of fuel, and ha\’ing seen this 
 engine in operation, I am quite of the opinion that it is to be the motor of the future, where not 
 exceeding 75 to 100 Horse Rower is required. 
 
 Yours very truly, 
 
 Renj. P'. R.\dford, 
 
 General ^^anagel■ The .\merican Tool & Machine Co. 
 
 'I'lIE 'I'AHNTON LOCOMOTIVE MEG. CO. 
 
 \Vm. R. Hii.i.ings, Agent and Treasurer. 
 
 Mr. Joshu.a. Merrill, Trcasu 7 -er. T.xun'ton, Mass., April 27, 1889. 
 
 Woodbury, Merrill, Ratten &: Woodbury Air Engine Co., 
 
 8 Exchange Rlace, Roston, Mass. 
 
 Dear Sir, — In reply to your request for an expression of our views upon certain points con- 
 nected with your Air Engine, we take pleasure in saying that we have examined on several occasions, 
 and with considerable care, the engine now in operation at South Roston; that we believe that this 
 engine marks an important advance in the progress of the Air Engine towards practical perfection ; that 
 the economy of fuel, indicated by the tests made by Mr. Rarrus and others, is remarkable, and that we 
 are ready to make arrangements with you for the construction of your Air Engine, of such sizes as you 
 may name and from such patterns and drawings as you may furnish. 
 
 Yours very truly, 
 
 'Ral'nton Locomotive Meg. Co. 
 
 Hy Wm. R. Billings, Agt. and Treas. 
 
 Col. Franklin Fairbanks, Prest. E. K. Whitney. I'ice Pres. P. F. Hazen, Sec''y^ St. Johnsbury, \'crmont. 
 
 W. P. Fairbanks, Treas. W'arren S. Mili-, CJt. Ex. Cant. E. A. Mildank, Afgr.^ i6i Franklin Si., Poston. 
 
 STAX 1 ).\R 1 ) ELECTRIC COMRAXY, of Vermo.xt. 
 
 (Whitney System.) 
 
 Manufactured by llie E. & T. f'AIRHAXKS & CO., St. Jolinsbury, Vt. 
 
 Mr. Joshua Merrill, Treasurer, Bo.ston, Mass., April 30. 1888. 
 
 Woodbury, Merrill, Ratten & Woodbury Air Engine Co.. 
 
 8 Exchange Rlace, Roston, Mass. 
 
 Dear Sir, — iMy continued absence from Roston has alone prevented my calling on you during 
 the past two weeks. There are several parties who are interested in the reports of the tests made on 
 your engine, and it is my intention to accompany them when they make their inspection. If they see 
 the engine as I have seen it, there is no doubt about their verdict. It is hard to convince anyone that 
 there is an air engine of any practical use. that is. an engine capable of delivering any considerable 
 amount of power, — 20 or 30 Horse Power, for instance. Seeing is believing, however, and the most 
 skeptical must give way after investigaiing your motor. Rroving as you do that a Horse Rower may be 
 delivered with an expenditure of 2.37 lbs. of coal per hour, and that result accomplished without boiler 
 or steam, you must attract the attention of the power using public. For use in hotels and apartment 
 houses, where electric lighting machinery or ventilating apparatus may be required, your engine is 
 particularly well adapted. Again, in locations where the use of steam is imjjossible on account of lack 
 of boiler room, you stand ready to supply the situation. I am convinced that the Air Engine, in the 
 present form, constructed by your company, is a motor of decided value, not alone on account of its 
 economy but also on the score of safety. 
 
 ^'ery truly yours. 
 
 ^\^^I. C. ^^'ooPWARD. Eleetrieal Engineer. 
 
GRANT LOCOMOTIVE WORKS. 
 
 New York Office, ^3 Wall Si. 
 
 Mk. Jo.sHiA Merrill, Treasurer, Paterson, N. J., April i6, 1889. 
 
 Woodburv, Merrill. Patten &; M’oobury Air Engine Co., 
 
 8 Exchange Place, Poston, Mass. 
 
 Dear Sir. — Yours of nth inst.. with report of the tests of your Air Engine, by Mr. Barrus, M.E., 
 to hand. 1 have read it with interest, and can see no reason why your engine should not have a large 
 sale as soon as you are ready to put it on the market. Respectfully, W. W. Evans, Sup't. 
 
 THOMSON-HOUSTON ELECTRIC CO. 
 
 ELECTRIC LIGHTING AND POWER. 
 
 Works, Lynn, Mass. Principal Office, 620 Atlantic Ave., Boston. Western Office, 148 Michigan Ave, Chicago. 
 
 Mr. Joshua Merrill, Treasurer, Boston, May 3, 1889. 
 
 Woodbury, Merrill, Patten & Woodbury Air Engine Co., 
 
 8 Exchange Place, Boston, Mass. 
 
 Dear Sir, — In accordance with your request, I desire to submit my opinion regarding your new 
 Air Engine, 1 have been very much interested in reading the report of Mr. Barrus in regard to the 
 test made on same by him, and was largely influenced by reading these reports to go and make a 
 personal examination of the 30 Horse Power Engine now completed. 
 
 It is my opinion, based upon some little experience in steam engineering, that in this engine you 
 have made a decided step in advance on the subject of air engines. I am confident that in this you 
 
 have a perfect,- practical, and exceedingly economical engine ; and should you decide to construct a 
 
 100 Horse Power for your first size, you may consider that you have an order for one from this company. 
 
 Very truly yours. 
 
 Engineering Department Thomson-Houston Electric Co. 
 
 H. C. Patterson, Elec. 
 
 .Mr. Joshua Merrill, Treasurer, Boston, May 3, 1889. 
 
 Woodbury, Merrill, Patten &: Woodbury Air Engine Co., 
 
 8 Exchange Place, Boston, Mass. 
 
 Dear Sir, — In the year 1877, as manager of the Nashua Iron &: Steel Co., I made an arrange- 
 ment witli you to manufacture the first experimental engine, to be propelled by means of the heating 
 
 and the cooling, in rapid succession, of the air confined within the cylinders and “heater” of the 
 macliine. So much success was secured at that time as to give me an earnest of very promising results 
 to come, and consequently, I have, from time to time, become somewhat familiar with the successive 
 improvements you have added to the engine. On my last visit to the machine, a few days ago, I was 
 more tlian ever impressed with the perfection of the motor, its simplicity, its reliable efficiency as to 
 power, its smoothness and regularity of motion, and the ease with which it is managed. I am convinced 
 that you have made very great strides towards a safe, efficient, and reliable means of motion, and have 
 no doubt tlie engine will, in large degree, supersede the use of steam as a means of mechanical power. 
 1 hope your perseverance and large outlay will be fully rewarded. 
 
 Truly, &c., Moses A. Herrick. 
 WRIGirr ELECTRICAL ENGINEERING CO., 
 
 7 .( FEDERAL STREET, 
 
 Alex. P. Wright, Managing Director. 
 
 Mr. JdsHUA Merrii.l. Treasurer, Bo-STON, IMass., U. S. A., May 4th, 1889. 
 
 Woodburv, Merrill, Patten & Woodbury Air Engine Co., 
 
 8 Exchange Place, Boston, Mass. 
 
 Dear Sir, — I was much interested during my visit to see your Air Engine, and have given it 
 considerable thought since. If it will come up to the claims made for it, and I believe it will do so 
 and more, wiien suitable sizes are ready for the market, the field for its application in Electric Lighting 
 will be \ery wide, and it will undoubtedly come into use to a large extent for this purpose. 
 
 Vours truly, Alex. P. Wright, 
 
 Expert Coitsultiiig and Electrical Engineer. 
 
Quotations from various Authorities with Explanatory Notes. 
 
 The theoretical ad\'antat;'e.s of air as a safe and economical ag'ent for converting heat 
 into power have long been recognized by scientists and mechanicians ; but efforts, to use 
 it practically, have been attended, hitherto, with such great difficulties, as to i)revent its 
 general adoption as a motor. 
 
 But, notwithstanding the obstacles have aijpeared excessive, the most eminent authorities 
 on mechanics have been confident that air is destined, to supersede steam. 
 
 Appleton’s Cyclopa'dia of Applied Mechanics, vol. I., page 620, published in 1880, states: 
 
 “The engines that have just been described are necessarily limited to comparatively low pres- 
 sures, and hence must be very bulky when designed to develope considerable power. This limitation 
 
 is an essential condition of their design, because the original pressure of the air which is compressed 
 and heated is that of the atmosphere. If, however, the working air be confined in the machine, 
 and originally compressed to a high pressure, this difficulty disappears. Thus, suppose it is found 
 practicable to maintain a temperature in a given air-engine sufficient to double the original pressure 
 of the air. Then, if the air were admitted at the pressure of the atmosphere, the available pres- 
 sure, after heating, would be about 15 lbs. per square inch. But if the supply of air were drawn 
 from a reservoir, in which the pressure was 60 lbs. per square inch, the effect of increasing the 
 
 temperature to the same point as in the former case would be to double the original pressure, 
 making 1 20 lbs. per square inch. It seems strange that the majority of inventors should have 
 ignored this significant principle.” 
 
 IIV employ this principle of using air compressed to a pressnre of 60 lbs. per square inch. 
 
 And on page 623 the following occurs : 
 
 “ It has been predicted by more than one prominent engineer that the steam engine will vet 
 be superseded by the air engine.” 
 
 In a work by a well known writer, John Bourne, entitled “Recent Improvements in the Steam 
 Engine,” published in London, in 1874, on page 330, he states : 
 
 “ The wasteful character of the steam engine as a source of motive power, has now become 
 
 so widely known that public attention has been directed with more ardor than heretofore, to the 
 
 discovery of expedients for its supersession. Of these alternative expedients, the most promising 
 seems to be some form of air or gas engine. But all the air and gas engines, heretofore devised, 
 
 labor under this radical defect, that only low pressures can be employed in them, and hence only 
 
 a portion of the energy of the heat can be transformed into power. So soon as this fault shall 
 
 have been corrected, without the introduction of other sources of loss, the steam engine will be 
 superseded ; and there are good grounds for concluding that this result is not far distant, but will 
 soon be achieved.” 
 
 We have remedied this defect, unthont the introduction of other sources of loss. 
 
 Knight’s American Mechanical Dictionary, published in 1874, vol. I, page 35. states: 
 
 “ In this engine the air received heat at the temperature of 650° Fah., and discharged the 
 lost heat at that of 150*^ Fah. The efficiency of a theoretically perfect engine, with those limits of 
 temperature, would be 0.45, and its consumption of coal 0.73 of a lb. per horse-power per hour. 
 
The actual consumption of coal per horse-power per hour was about 2.2 lbs., being three times the 
 consumption of a theoretically perfect engine, and corresponding to an actual efficiency of 0.15 or 
 one-third of the maximum theoretical efficiency. 
 
 The following is a comparison of the consumption of bituminous coal of specified quality, per 
 horse-power per hour : 
 
 1. For a theoretically perfect engine, working between such limits of temperature as is usual 
 in a steam engine, 1.86 lbs. 
 
 2. For a double acting steam engine, impelled to the utmost probable extent, 2.50 lbs. 
 
 3. For a well constructed and properly worked ordinary steam engine, on an average, 4.00 lbs. 
 
 Referring to above, especially to paragraph 3, ivc direct yotir attention to the fact, that as 
 per test of George H. Barms, herezuith submitted, the consumption of coal per horsc-pozver per hour 
 of our engine is but 1.54 lbs. 
 
 Science has thoroughly demonstrated the theoretical economy of heat which results from the 
 use of the regenerator. Rankine in his ‘‘ Manual of the Steam Engine and other prime movers,” 
 
 published in London, in 1876, states on page 353 : 
 
 " By thus storing and re-storing a certain quantity of heat, the alternate lowering and raising 
 of the temperature of the air is effected without the expediture for that purpose of any heat from 
 the furnace, except such as is requried to supply the waste of heat that occurs in the regenerator ; 
 that waste, according to experiment, being from one-tenth to one one-tzoentieth of the whole quantity 
 of heat required to raise the temperature of the air at each stroke.” 
 
 Our engine is provided zvith the most perfect regenerator ever made, by the use of zuhieh, zve 
 obtain the highest eeononiical results. 
 
Engines of the following sizes will be constructed and put upon the 
 market with as little delay as possible: — 
 
 Xo. 
 
 r ) . 
 
 K i V e Horse T^o we r . 
 
 Xo. 
 
 10. 
 
 Kifteen Horse I^cower. 
 
 Xo. 
 
 lo . 
 
 Tloirt\" Hive Horse Hower. 
 
 Xo. 
 
 20. 
 
 Si^t 3 " Horse Hower. 
 
 Xo. 
 
 2o. 
 
 Oivie Hiuodrecl Horse F*o\\^er 
 
 The rapid advance lately made in the economy of this engine has con- 
 vinced the inventors from the data they have developed, that there is no doubt 
 but that engine number 25, and probably number 20, will run on i lb. of coal 
 per Indicated Horse Power per hour, and 1.6 lbs. per Delivered Horse Power 
 per hour. 
 
 A large number of orders for engines of various sizes, to be delivered as 
 soon as they can be constructed, are already offered to the Company. 
 
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