NOVEMBEE 27, 1896.] 



SCIENCE. 



779 



producing a non-conducting working cylin- 

 der and thus of approximating the real to 

 the ideal thermodynamic machine, a method 

 discussed by the writer at some length in a 

 recent issue of the Transactions of the U. S. 

 Naval Institute. 



The following is a summary of the con- 

 clusions presented before the American 

 Society of Mechanical Engineers : 

 ^ '^ ^ '^ 



Opinion seems substantially unanimous, 

 a,nd all testimony confirms the conclusion 

 that superheat may effect large net econo- 

 mies. Collating the results of about fifty 

 a,uthentic and well-conducted experiments, 

 it is found that the gain in fuel, by the in- 

 troduction of superheating, ranges from ten 

 to fifty per cent, of the fuel used with wet 

 steam ; that about 100 degrees superheat, 

 on the Fahrenheit scale, gives usually com- 

 plete extinction of initial condensation ; that 

 «ven fifteen or twenty degrees will make an 

 important gain in reduction of internal 

 wastes ; that every application of this sys- 

 tem, discreetly effected, returns several 

 times — actually from two to ten times — its 

 cost in heat expended ; that the largest re- 

 turns are secured by the smallest quantities 

 of superheating; and that the indications 

 are, so far as we can to-day judge from 

 earlier and contemporary practice, good 

 engineering in this direction pays, and pays 

 well ; the limit being found at that point, 

 continually becoming more remote and at a 

 higher and higher temperature, at which 

 excess of temperature begins to cause 

 rapid destruction of the superheating appa- 

 ratus, and consequent expense and danger 

 in such degree as to become a large and 

 more than counterbalancing element. The 

 average of fifty-two cases observed hy the 

 writer gives a gain of twenty-six per cent, 

 with a superheat of 105 degrees Fahr. The 

 average gain with compound engines exam- 

 ined is twenty per cent. With a lower but 

 uncertain amount of superheating, in a 



majority of the cases reported the superheat 

 not having been measured. In cases aver- 

 aging about fifty degrees superheat, the 

 gain was twenty per cent., and this is prob- 

 ably not far from the average for all. 



^ ^ ^ ^ 



Thus, one thermal unit, one pound of 

 steam or of fuel, or one dollar, expended in 

 reduction of this internal waste, returns 

 three ; and a profit of three hundred per 

 cent, pays, in turn, the excess of cost of 

 maintenance of superheating apparatus and 

 incidental costs and repairs at engine and 

 at boiler. 



"Where the gain by use of superheating is 

 less, the proportion of profit to expenditure 

 is, as a rule, greater, since the effect of the 

 first few degrees of elevation of temperature 

 and of superheat is by far the most effective 

 in reduction of initial condensation. 



The conclusions of the writer are the fol- 

 lowing : 



(1) Superheated steam, as hitherto em- 

 ployed in the steam-engine, has absolutely 

 no purely thermodynamic value. It neither 

 raises the upper limit of temperature nor 

 depresses the lower ; it gives no increased 

 range of temperature of the cycle ; the value 

 of the maximum measure of ideal efficiency, 

 (Tj^—T^)/T^, is in no manner altered by its 

 introduction into the system. 



On the other hand, it is evident, from a 

 study of the physics and thermodynamics 

 of the case, that, could any way be found 

 of practically working superheated steam, 

 safely and with economy in its production, 

 it would permit a thermodynamic gain only 

 limited by the extent to which the range 

 T^—T^ could be thus expanded. 



(2) Superheating has for its sole pur- 

 pose and result, in the steam-engine to-day, 

 the extinction or reduction of the internal 

 thermal wastes of the engine, consequent 

 upon the phenomenon known as initial or 

 ' cylinder condensation.' Here it is extra- 

 ordinarily effective, and a small quantity of 



