EFFECT OF DIFFERENT FOE MS OF SETTING. 51 



order that the cost of fuel and labor for a 1,000 horse-power 

 plant shall be equal to that which obtains when Cumberland 

 coal is used at $4.56 per ton. 



If the economic result with petroleum goes up to 18 pounds, 

 the price of oil per barrel to equal Cumberland coal on this 

 basis is $1.18 cents. It is to be noted that these figures are 

 based upon a barrel of 50 gallons. If the barrel is taken to 

 be 42 gallons, the prices become 82.7 cents for an evaporation 

 of 15 pounds, and 99.1 cents for an evaporation of 18 pounds. 



5. MISCELLANEOUS DISCUSSION. 



The general subject of boiler economy has now been exam- 

 ined, so far as it is affected, first, by the character of the steam, 

 that is, as to its being saturated or superheated ; second, by 

 the general arrangement of the heating surface and the condi- 

 tions under which the boiler is worked; third, by the type of 

 the boiler ; and fourth, by the character of the fuel burned. 

 These may be regarded as the more noteworthy divisions of 

 the subject. Incidental matters remain to be taken up, and 

 these are quite as interesting, and sometimes almost as import- 

 ant, as the main questions thus far considered. 



An important question connected with the economy of 

 boilers is that of the effect which the form of setting has, 

 where the boiler is externally fired. Questions arise in the 

 setting of horizontal tubular boilers as to the distance between 

 the grate and the shell, and between the top of the bridge wall 

 and the shell ; the shape of bridge wall, whether curved 

 upward to conform to the curve of the shell, or simply left 

 flat; the arrangement of the front of the bridge wall, whether 

 inclined or vertical ; and the arrangement of the space behind 

 the bridge wall. Although the tests furnish no direct compar- 

 ative data on these subjects, useful information may be drawn 

 from individual results. It is significant that the highest 

 results given are in some cases obtained with one form of 

 setting and in some with another form. Boiler No. 9, which 

 gave a high result with anthracite coal, has a flat bridge wall 

 with perpendicular front, and the space behind the bridge is 



