002 A (KNTrKV's PK(>(JKKSS OF THi: s;TKAM KNMilNK. 



Tlu' <-urvo iit the left ol" tliis (li;ii:r:iiii icprcseiits llic idral vasv of 

 Caniot and its iiid'casint;- ctticit'iicy as the jirrssiirt' ciiiployt'd i-iscs 

 from tlu' low Hgurcs of tlu' iiiiddlr <»f the (•ciitiuy and earlier to the 

 maximum for the advanced ])raetiee of leading' eiiuineers of to-day. 

 The costs of the hoi'se])o\ver rano'e from between lif and {'■) pounds of 

 steam per hour at the minimuiu ])ressur(> to ap])roximately !• pounds 

 at loo pounds ])ressure. s and 7. rospecti\ely. at 2<M» and 800 pounds 

 pressure, and al)out i'i'i at i')O0. With l.(K»o pcunuls hoiUn- })ressure the 

 tio"ure should drop to about <» pounds of steam jx'r horsepower per hour. 



It seems entirely praetieal)le. so far as experience to date goes, to 

 secure quite as close an approximation to the ideiil <'ase in the real 

 engine at high as at low pressures. A waste* of from 25 to 50 per cent 

 may l)e taken as a coiumon range of etticiency loss in steam engities 

 ))y reputable t)uilders. nudtiple-cylinder engines being employed for 

 all pressures exi-eeding loo pounds boiler ])ressure, and the steam 

 jacket and moderate superheating being adopti'd for the mo>«t efficient 

 machiiu', especially when, as is usual with j^umping engines, having a 

 low piston s])e«>d. Curves ai'e insci"ibed on the diagram with these 

 amounts of waste, and the area bounded l)y them may be taken as that 

 occupied by modern good practice up to the present limit of good 

 and common practice. The facts that the trend of existing and earlier 

 practice so clos«dy follows th«'se lines and that the only expei-iments 

 scientitically con<lucted and recorded to date for the maxinuun limit 

 sho>v the accuracy of the preceding conclusion, give us good basis for 

 these general deductions. 



The weight of steaui pei" indicated horsepower per hour is here gi\ en 

 as Tr= IS -=- log y> for the ideal case, while ex})eiience gives about 

 ir= 25 -^ log y> for good practice up to the highest limits yet accepted 

 as standard. On the diagram, tig <>. are inscrilx'd. also, the dates at 

 which th(* noted efficiencies were attained by good l)uilders generally 

 and the approxiuiate record for the close of the century. It will be 

 found that these chronological observations fall into a fairly smooth 

 curve, and the deduction is as inevitable that not only will steam })res- 

 sures and expansion ratios continue to increase in the immediate future, 

 but also that improvement may be expected to continue in this direc- 

 tion, slowly with respect to rising efficiencies, rapidly in increasing 

 pressures, as improved forms of steam l)oilers make it safe to emplo}' 

 such pressures, and as users and builders gi'adually yi<dd their long- 

 existing prejudices against high pressures. 



We may expect in a very few' years more to see steam pressures for 

 engines of high efficiency range from 500 to 1,000 pounds per square 

 inch, the quality of the steam being maintained at a high fraction by 

 preliminary superheating on at least a moderate scale, with reheater 

 superheating between cjdinders in series, and with jackets on heads of 

 low-speed pum|)ing engines, as now practiced. At the rate at which 



