38 BOILER TESTS. 



common boilers produced. Here the heating surface bears a 

 ratio to grate surface of 57.9 to 1, and the ratio of grate to 

 tube opening is 6.7 to 1. Under these circumstances, which 

 are most favorable, a high result would be expected from any 

 form of boiler, and the detached furnace cannot reasonably lay 

 claim to any special advantage. 



The boiler with two furnaces for alternate firing, No. 18, a 

 system which is evidently of use only in cases where bitumi- 

 nous coal is burned, gave a result much below that of a com- 

 mon boiler. The temperature of the escaping gases was 472 

 degrees, which is too high for the best economy. But this 

 unfavorable condition does not wholly account for the deficiency, 

 the evaporation being 10.93 pounds. The evidence of this 

 single instance is that the double furnace type of boiler is infe- 

 rior to the common type. 



The boilers which have a water leg for the front of the furnace, 

 differ so little from the common boiler that neither loss nor 

 gain, if either occurred, could with reason be attributed to this 

 method of construction. Boiler No. 9, which is fitted in this 

 manner, gave an evaporation with anthracite coal amounting to 

 11 .24 pounds. This excellent result is largely due, no doubt, to 

 the new condition of the boiler and to the favorable proportions 

 which existed. 



, The boilers in which a double passage of the products of 

 combustion occurred are Nos. 4, 12, and 38. Only one needs 

 to be considered, viz., No. 12, the others being foreign to the 

 discussion. Here, a favorable result is produced with anthracite 

 coal, the evaporation being 11.20 pounds of water from and 

 at 212 degrees per pound of combustible, and here, again, 

 favorable conditions lent their aid. The result obtained with 

 bituminous coal is rather low. According to the conclusions 

 which we have reached as to the best proportions of boilers, 

 the tube opening is insufficient, being only a little more than 

 one-half of that laid down for bituminous coal. This form of 

 boiler is not well adapted for securing a large tube opening, 

 because with a given number of tubes only half of them can 

 be employed for carrying the products in one direction. The 



