TEANSACTIONS OF SECTION G. 807 



Tinced from general observation that it is far more efficient and economical than the 

 ordinary form. One great reason lies in the fact that the heat is all imparted to 

 the boiler surfaces by direct contact of solid fuel, or radiated from the solid fuel 

 which is almost touching the plates. It is the author's intention to carry out 

 careful experiments with this form of boiler. 



6. The Compound Steavi Engine.^ By J. Richaedson. 



After a brief introduction defining what is meant by a compound engine, and 

 stating how the economy of one kind over another should be measured, the paper 

 dealt with the various steps in the development of the steam engine so far as 

 steam economy is concerned, and traced its progress up to the present date, giving 

 illustrations of engines using low pressures non-expansively and expansively, high 

 pressures non-expansively and expansively, and showing the use and value of the 

 steam jacket and separate condenser. It was stated that though there is no 

 theoretical limit to the economy to be obtained by extremely high degrees of 

 expansion, yet there are practical limits which are soon reached for non-condensing 

 engines. In these the steam must not be expanded below the atmospheric pressure, 

 or back pressure and waste of power is the result. To prevent this a very high 

 initial pressure must be used, and as with 140 lbs. boiler pressure, or 155 lbs. 

 absolute, steam expanded ten times leaves only half a pound pressure in the 

 exhaust, this is fixed upon as practically the most useful degree in non-condensing 

 engines. 



Reference was made to the use of steam at much higher pressures — 500 lbs. and 

 upwards — and used in three or more cylinders ; yet the difficulties attending the 

 production of steam at these high pressures and temperatures and the maintenance 

 of the working parts of the steam cylinders are stated to be such as more than 

 counterbalance the advantages to be obtained from their use. 



It could be shown that expansion could be carried to such an extent that 

 while the efficiency of the steam, considered merely as steam, would continue to 

 be increased, a point would be reached at which it would be barely able to move 

 the piston it was intended to propel, and when, therefore, the engine in which it 

 worked would be practically useless. 



A comparison was instituted between the single cylinder expansive engine 

 and the various classes of compound, namely, those which have the. low-pressure 

 cylinder parallel with the high as in the Woolf engine, on the same centre line as 

 in the tandem, and those with cranks at right angles, tlie advantages and dis- 

 advantages of each type being pointed out. The proportions to be maintained 

 between the two cylinders were next considered, and the advantage of the inter- 

 mediate receiver and heater were referred to ; the advantage of expansion gear 

 to the low-pressure cylinder, not merely for the purpose of securing greater 

 economy, but also for the sake of securing uniform distribution of the load be- 

 tween the two cylinders, was pointed out. Illustrations and diagrams of the earlier 

 types of engines were given, and indicator diagrams .showing different methods of 

 distributing steam, together with large diagrams showing modern tandem com- 

 pound horizontal engine, coupled compound horizontal, and coupled compound 

 with locomotive boiler combined, as well as details of the valve gear of each, and 

 the method of automatically regulating the supply of steam. 



The compound engine as now constructed is claimed to be the most perfect 

 form of steam motor, comparatively small engines under 100 H.P., and without 

 condensation, giving a horse power for somewhat under 20 lbs. of steam per hour, 

 while large engines when fitted with condensers have been shown to use no more 

 than 12 lbs. of steam per horse-power per hour ; at the same time the construction 

 of compound engines has been so simplified that they have no more parts, and are 

 no more difficult to manage, than ordinary double-cylinder high-pressure engines. 



' Published in extenso in Industries, Sept. 10, 1886. 



