58 BOILER TESTS. 



where the temperature of the flue is not far from that laid 

 down in another part of the paper for boilers giving most 

 economical results, and it is seen from the many instances 

 recorded that the exigencies of boiler work often bring about a 

 much higher flue temperature. The flue heater thus has a 

 useful place, not only in a few instances but in a large majority 

 of boiler plants where the water is supplied in a comparatively 

 cold state. In the cases given, there is a reduction of 128 

 degrees in the temperature of the gases, and an increase of 79 

 degrees in the temperature of the water. Each one per cent, 

 added to the evaporation corresponds to a reduction of about 

 13 degrees in the temperature of the escaping gases. 



It is important to note the effect which the use of the heater 

 has upon the draught. The amount of draught suction which 

 existed in some of the above examples and in one additional 

 example, together with information regarding quantity of coal 

 burned and other matters bearing on the question, are given in 

 Table No. 10. 



The effect of a reduced temperature of the escaping gases, 

 which always accompanies the employment of the heater, is 

 seen, in every one of these instances, to reduce the draught 

 power of the chimney. In Boiler No. 59 the temperature is 

 reduced from 645 degrees to 365 degrees, and the draught 

 from j 4 ^ of an inch to ffi Q of an inch, or 22 per cent. This 

 is with an 80-foot chimney. In the last case a reduction of 

 temperature from 575 degrees to 373 degrees is accompanied 

 by a reduction of draught from ^ {} of an inch to f^ (} of an 

 inch, or 29 per cent. This is with a 140-foot chimney. 

 Although the general effect of the flue heater in this respect is 

 unfavorable, a larger amount of draught is required to operate 

 the boiler, in every instance where the average draught is given, 

 when the heater is thrown out of use. , This is not due to any 

 peculiar action of the heater but evidently to the increased 

 quantity of coal which must be burned in order to make up for 

 its absence. It may be concluded that a plant of boilers work- 

 ing to the full capacity of the chimney without a heater, will 

 have no difficulty in producing the same amount of steam, 



