40 BOILER TESTS. 



is an equivalent evaporation of 12.75 pounds of water from 

 and at 212 degrees per pound of combustible. We have a 

 result here which surpasses any given in the paper by horizon- 

 tal tubular boilers. Vertical boiler No. 58, though of a 

 different arrangement, gave a result which, without allowance 

 for superheating, is precisely the same. These instances are 

 not of sufficient number to establish the vertical boiler as one 

 of superior economy to the horizontal boiler, but they show 

 that, when properly designed, it is at least the equal of the 

 horizontal boiler. 



The three case.s of cast-iron sectional boilers, viz., Nos. 61, 

 62 and 63, give comparatively poor results. The unfavorable 

 showing is due in some degree to unfavorable conditions. In 

 every one, the ratio of heating surface to grate surface is below 

 that which has been given as essential to economical work. In 

 all three cases the effect of this departure from correct prin- 

 ciples is seen in the high degree of flue temperature. There 

 is nothing in the construction of the boiler to prevent the 

 employment of any proportions between heating surface and 

 grate surface which may be desired, and it is not improbable 

 that the results would have been equal to those of the tubular 

 boiler if suitable proportions had existed. 



There is some variety in the economic results produced by 

 the water-tube boilers. Out of the whole number of boilers 

 given, amounting in all to nine, only one appears io reach the 

 standard laid down for good economy. The principal results 

 are given in Table No. 6. Examining these figures closely, it 

 is seen that the result referred to (Boiler No. 65,) was pro- 

 duced by boilers having a sufficient ratio of heating surface to 

 grate surface, and in which there was a high rate of combus- 

 tion and a low temperature of the flue. In addition to this, 

 the boilers were comparatively new. These are conditions 

 which, as already shown, usually lead to high performance. 

 The inferior results given for the remaining water-tube boilers, 

 with one exception, can be attributed to waste heat at the flue. 

 In Boiler No. 69, the high temperature seems to be due to a 

 deficiency in the quantity of heating surface. In most of the 



