~apers.1 ROBERTSON ON THE STATIONARY STEAM-ENGINE. 353 (Paper No. 3188.) ‘‘ The Evolution of the Stationary Steam-Engine.” By ANDREWROBERT ROBERTSON. INthe time of Newcomen the steam-engine was used only as a means of driving a pump, as the natural outcome of the older idea of elevating water by displacing it with steam. Savery’s engine, or pump,worked on the latter principle, but the limits of the conditions under which it would act were so quickly reached, that Newcomen’s engine soon after its advent almost entirely replaced it ; but although at that time unable to do the work demanded of it, modern methods and knowledge have enabled Savery’s engine to reappear in the many forms of Pulsometer pumps. Early engines were called “ fire-engines,” and are now classed as“atmospheric,” the steam having been used not as a direct means of driving, but only to displace t,he air in the cylinder, which, in condensing, produced avacuum on one side of the piston and allowed the pressure of the atmosphere to act on the other side. Since the daysof Newcomen the name most intimately connected with the steam-engine is that of James Watt, and in his hands it assumed a shape and embodied principles which later engineers have not alteredbut only added toand improved. To show, therefore, that the main features and principle of the engine as laid down by Watt and his contemporaries differ only in detail from those employed by successive experimenters and designers will be the mainobject of this Paper. Watt began his study of the principles of Newcomen’s engine by investigating the quantity of water necessary to condense a givenamount of steam, withthe object of determiningthe temperature corresponding to varioussteam pressures. These experiments soon showed him that the Newcomen engine required more water to effect condensation than the volume of steam in the cylinder warranted. This apparent anomaly gave Watt his clue. Why should the engine inpractice demand more condensing water than was necessary to condense the same volume of steam experi- [THIE INST. C.E. VOL. CXXXVIII.] 2A Downloaded by [ Columbia University] on [15/09/16]. Copyright © ICE Publishing, all rights reserved. 354 ROBERTSON ON THE STATIONARY STEAM-ENUINE. [Selected mentally?The only answer that reasoning gave was, thatin some way more steam than the content of the cylinder was being used at everystroke. Further consideration pointed to the fact that when thesteam was admitted into the cylindera considerable amount was condensed by the walls cooled by the condensation of the previousstroke. The separate condenser was thus suggested as a means of preventing this excessive cooling and reheating of the cylinder, and Watt wasled to announce his leading principle, viz., that at allcosts the temperature of the cylinder mustbe kept as high as that of the entering steam. The success attendingthe first experimentsgave Watt such encouragement that he seriously took up the improvement of the engine, andthis led to the following alterations and improve- ments that made him famous. The separate condenser; the use of air-pumps;the steam-jacket ; the expansive use of steam; governing the speed of the engine ; guiding the piston-rod ; im- provement of cylinder details ; the, mannerof converting recipro- cating into rotarymotion ; the admission of steam to both sides of piston ; the steam-engine indicator ; the engine-counter and the pressure-gauge. The separate condenser led to the use of the air-pump, as other- wise the vacuumformed by thecondensation of the steam gradually began to fail owing to the accumulation within the condenser of the gases: brought in with the steam, and although Watt knew how to make a Torricellian condenser the height necessary was not available, and the air-pump was the natural alternative. The steam-jacket was part of the first principlementioned ; the expansive use of steam, however, was the outcome of a separate set of observations though brought about by noticing the power given up by steam expanding into the separatecondenser. The governing of the speed came as a necessary adjunct of the automatic working of the engine which now did not require that every stroke should be watched. The parallel motion replaced Newcomen’s chain and sector, and must be regarded as a very beautiful means of overcoming the difficulties caused at that time by imperfect workmanship which rendered theslipper guides now usedalmost impossible. The cylinderdetails wereimproved inworkmanship and design, stuffig-glandsand properly madepistons were used, and ultimately correctly bored cylinders became a possibility. Theconverting of the reciprocatorymovement of thepump into a rotary one required for driving a fly-wheel was most simply performed bythe crank and connecting-rod ; butthis ancient Downloaded by [ Columbia University] on [15/09/16]. Copyright © ICE Publishing, all rights reserved. ~apers.1 ROBERTSON ON THE STATIONARY STEAM-ENGCINE. 355 device was patentable at the time, and Watt wasforestalled, hence his invention of the sun-and-planet gear. The admission of steam to both sides of the piston completed the making of the steam-engine type, and the recording instru- ments, theindicator, the pressure-gauge, andthe revolution- counter, enabled Watt to determine if his designs developed the results anticipated. Watt’s work was essentially practical in the true sense of the word, in that he combined a thorough study of what theory he could master with his experimenting-in fact, his philosophy was absolutelyexperimental. In all work, however, theresults obtainedare apt tomake theoriginator pay more attentionto engineering details rather than to pure philosophy, and as a result the precise study of abstract principle is generally leftto theorists who make a life-work of such subjects. In Watt’s case there was a commercial end in view; and while, therefore, the engine owes most of its details to Watt, it owes much of its modern efficacy to those who, making thermo-dynamics their special study, put Watt’s discoveries into scientific form, laying down certainrules and principles which all heat-engines should follow. Watt himself enjoyed the friendship and help of Dr. Black, of Glasgow ; but it is to Sadi Carnot that the honour must be given of originating the study now called Thermo-dynamics, which has been inseparable ever since from the proper understanding of the steam-engine, all problems of the modern heat-engine of whatever form being discussed withdue consideration of bothThermo- dynamic theory and practice ; the abstract theory being limited bythe possibilities obtainablein practice, andif the word is properly used including these limitations as part of the theory. Since Carnot’s time the theory has been more clearly elucidated, and the limitations of practice not only more clearly defined, but diminished, and the two brought into better relation, and there- fore the theory is now placed in due and proper relation to the expediency of manufacture and the use to which the engine is to be put. Havingstated the principle of theseparate condenser and worked in accordance with it, Watt obtained a result considered satisfactory ; but his suocessors, aided by the theorist, havebecome more familiar with the principles and apply them further. The effect of the cold cylinder is now calleci initial condensation, and after Watt’s time it came to be recognized that lin removing the condenser from the cylinder all thecauses of initial condensa- tion did notdisappear, and means of decreasing them were sought. 2A2 Downloaded by [ Columbia University] on [15/09/16]. Copyright © ICE Publishing, all rights reserved. 356 ROBERTSON ON THE STATIONARY STEAM-ENGINE. [Selected The steam’enters the cylinder ata pressure above that at whichit leaves it, and therefore the incoming steam meets a cylinder cooled bythe exhaust. Consequently modern engineers, intrying to make the difference of temperatures of entrance and exit as small as possible, compound the engine. Thisaction may fairly be described as a furthercarrying out of theprinciple of Watt’s separate condenser, and it may be accurately said that en,‘Vlneers have simply moved the condenser further from the engine. Com- pounding is aiso intimately connected with theuse of high-pressure steam, as the long ranges of expansion which would otherwise be necessary render it especiallyadvantageous. That the efficiency of the engine is raised by the use of high-pressure steam is clear when Carnot’s statement for the efficiency of a heat-engine is con- sidered. This shows that the efficiency of a perfect heat-engine dependswholly on the difference between thetemperature of entrance and exit of the working fluid, and though the steam- engine is not a perfect “ heat-engine,’’ it belongs to that class and is governed by the same thermo-dynamic laws. The value of Carnot’s statement of efficiency, Temperature of entrance - temperature of exit __ ~~~~ ~ ~ Temperature of entrance increases with the temperature of entrance, so that the higher the pressure the greater the efficiency, and modern practice therefore tendstowaras the highest pressuresconsistent with safetyand durability. High-pressure engines (so called) are mentioned by Watt in his patents, but he did not employ them. It was for Trevithick, his competitor, to be the pioneer of high-pressure steam, and next to Watt he must be considered as having exercised, the strongest influence on the later history of the engine. From a study of his life it would appear that he lived before his time with greatideals which,hampered by circumstances,he had perforce to leaveto others to perfect. Watt, content to make his engine as perfect as circumstances would allow him,outlined possibilities he considered beyond the power of his generation. Trevithick, on the contrary, went boldly at apparently insurmountableobstacles, and produced enginesthat would now be considered criminally unsafe. He drove his engines with high-pressuresteam generated in thecrude, leaky boilers of that day, at what must then have been considered a high speed.