4 2 BOILER TESTS. 



remaining boilers, it appears to be inefficiency of the surface 

 which causes loss, and this may be attributed either to deposit 

 of scale on the interior of the surface, or of soot and kindred 

 substances on the exterior. The last may be of frequent occur- 

 ence if the care of the boiler is neglected, more especially 

 since the exterior surfaces of water-tube boilers are difficult of 

 access, and are usually cleaned only by the use of a jet of 

 steam. On the whole, the water-tube boilers may be consid- 

 ered to be equal in economy to the tubular boilers, under the 

 conditions of comparison determined upon, that is, when the 

 conditions are favorable to economy. 



It should be noted that one test is given on a water-tube 

 boiler which shows an exceptionally high performance. This 

 is referred to in Part Second, being made on Boiler No. 68. 

 The evaporation obtained is 13.01 pounds, from and at 212 

 degrees per pound of combustible. The indication of this 

 single instance shows high possibilities of the boiler, though 

 it loses much of its force in view of the greatly inferior 

 result obtained from the same boiler on Test No. 134, made 

 two years later. 



There remains the single Galloway boiler, which was tested 

 with Cumberland coal. Unfavorable conditions for economy 

 exist here, and the low result produced is no different from 

 what would be expected. According to the principles govern- 

 ing economical work many times exemplified in this discussion, 

 there were disadvantages on every hand, and the test furnishes 

 no guide as to the capabilities of this form of boiler when 

 operated under favorable conditions. 



The general conclusion to be drawn from all these compari- 

 sons is that the economy with which different types of boilers 

 operate depends much more upon their proportions and the 

 conditions under which they work, than upon their type ; and, 

 moreover, that when these proportions are suitably carried 

 out, and when the conditions are favorable, the various types 

 of boilers give substantially the same economic result. 



