328 STATE BOARD OF AGRICULTURE 



only the steam eiij:;ine, tlie air en«jiiie, and tlie gas enjjine, but in fact 

 our liorses and onr own bodies are heat engines and tlie most efticient 

 heat engines W(^ liave, so far as the relali(»n of the (luantity of work 

 done by a given amount of fuel is concerned. If hay and oats cost no 

 more per ton than coal we might perhaps be running our factories by 

 horse power. 



A century ago the steam engine had just begun its work and the 

 industrial progress of the century has been largely due to the devel- 

 o])ment of the type of heat steam engine. It has been adapted to almost 

 every kind of work, and its elliciencv increasinl until now some of our 

 best power plants use less tluin a pound and a (jiuirler of coal per hour 

 for each horse power. 



But even now we are using only about fourteen per cent of the energy 

 contained in the coal. This fact leads many to think that there is a 

 wonderful chance yet for impi'oving the efficiency of the steam engine, 

 but our study of thermodynamics shows us that the efficiency of a 

 heat engine is limited by the change of temperature of the working fluid, 

 that an engine that would have an efficiency of one hundred per cent 

 would have to convert all the heat of the working substance into work, 

 which would mean that the steam or other working substance, would 

 have to leave the engine at the temperature of 460 degrees below^ zero. 

 If we could heat the steam to the temperature of red hot iron we could 

 not expect to obtain more than forty per cent of the energy of the 

 coal even with the steam exhausting into a condenser at a pressure of 

 only one-fifth of one atmosphere. It is easy enough to convert other 

 forms of energy into heat, but not so easy to convert heat into me- 

 chanical energy. 



Many attempts have been made to produce a more efficient engine 

 by using some other fluid instead of water but the laws of the conver- 

 sion of heat energy into mechanical energy are inde|iendent of the spe- 

 cial properties of any substance. Hot air engines have been used to 

 some extent, but their efficiency is low largely on account of the diffi- 

 culty in transmitting heat to and from the working substance. This 

 difficulty is overcome in gas and oil engines by mixing the fuel with the 

 air and thus generating the heat in the working substance itself. The 

 gas engine can work through a greater range of temperatures and hence 

 has a greater thermal efficiency than the steam engine, but it uses a 

 fuel that is more expensive in most localities. It has its advantages 

 and its disadvantages as compared with the steam engine. Largely on 

 account of the small amount of attention required, it is used quite 

 extensiA'ely for small powers, especially where the load is nearly con- 

 stant and the service intermittent. It is also finding a new^ field of 

 operations in utilizing the waste gases of blast furnaces, which are 

 peculiarly adapted to this tyjje of engine. 



When the gas engine first made its api^earance, again when the elec- 

 tric motor came into use, and still later when Tripler began to make 

 liquid air by the barrelful, we were informed that the steam engine 

 would soon be a thing of the past to be seen only in our museums, but 

 it is still doing business and promises to stay with us for some time 

 to come. Its only real rivals are the gas engine and the turbine. 

 The gas engine is finding its own sphere of usefulness in those places 

 for which it is best adapted but it will have to be greatly improved 



