40 ANNUAL OF SCIENTIFIC DISCOVKnT. 



by which it has been satisfactorily established that not more than 

 one-tenth of the entire heat of coal is on the average utilized by 

 steam engines. 



The author, Mr. "Richard Eaton, of Nottingham, England, then 

 discusses the i)ractical dilliculties encountered in the elVort to sub- 

 stitute heated air for steam, the principal of which is, as our 

 readers are already aware, the eftect of highly heated air upon 

 such metals as may be economically employed in the construc- 

 tion of machines. 



lie then })roceeds to give a brief history of the new aero- 

 steam motor, which avails itself of air expansion, using at the 

 same time steam, which removes the dilliculty above mentioned. 



In the first attempts at practically carrying out the s^'stem, the 

 arrangement adoi)ted was an ordinary high-pressure engine with 

 vertical boiler as used where fuel is cheap. An air-pump is 

 added, which is put in oi^eration by the action of the steam 

 engine. 



Thus, cold air is taken in by the air-pump, and is forced on in 

 its compressed state through an air-pipe, which, in the case 

 before us, is conducted tirst within the exhaust, then in a coiled 

 form down the funnel of the boiler, then past the fire, and finally 

 past a self-acting clack-valve at the bottom of the boiler into the 

 boiling water itself; rising naturally through the water, the air is 

 intercepted and subdivided by diaphragms of metal gauge. Thus 

 a twofold service is rendered by the contact of the elements, 

 the water becoming aerified and deprived of its cohesion and 

 prompted to a free ebullition, while the air on rising above the 

 water is saturated by the steam, and the two together pass on to 

 their duty in the cylinder where saturation assists lubrication. 

 The agitation of the water prevents scaling. 



In this form of the ai)paratus the power obtained by the in- 

 creased volume of the air forced in by the pumj) did not com- 

 pensate for that consumed in forcing it into the boiler. At the 

 same time there were encouraging indications which led to 

 further experiment. One of the air-pumjis being discarded, ex- 

 jieriments were made with waste-holes in the l)arrel of the otiier 

 pump, to ascertain what proportion of air admitted to the boiler" 

 compensated for compression. It was found that about 10 per 

 cent, of the effective consumption of fluid in the working cylinder 

 gave much better results. At tlie same time the cam motions 

 were discarded and the pumps left to their own unaided action. 

 In this form it is claimed that a gain in work done by the com- 

 bined air and steam engine was made of 42.5 per cent. 



Here, although a very remarkable relative economy was ap- 

 parent, it became obvious on consideration that danger of mistake 

 would arise in assuming this economy as absolute, inasmuch as 

 the duty i)erfoi'med, when contrasted with tiiat obtained from 

 engines of standard types, actuated by steam, was manifestly 

 low, and it seemed prol)ab!c tliat, as, by judicious imj)rovement 

 in details, the duty was made to ai)proximate more closely to fair 

 steam-engine duty, this relative economy might fall off consider- 

 ably, inasmuch as there would be less margin to economize upon. 



