ECONOMY OF FUEL EOR STEAM MACHINEET. 341 



placed over the heat, and Mr. Clarke clearly saya that the prin- 

 cipal efficiency of tubes is in the upper semi-circle, from which 

 it evidently results that the vertical tube would not be any more 

 efficient, if so much so, as the horizontal one, unless the advantage 

 resulted for the application of the heat to its exterior surface. 



There are some good suggestions, however, in the following remarks, 

 and especially in reference to contracting the ends of the tubes by the 

 insertion of ferrules, which we have ever viewed as a serious, though 

 unavoidable evil: 



"We now submit the following application of Montgomery's boiler 

 to the locomotive engine for increasing the efficiency of the steam- 

 generating parts. Retaining the common firebox shell, produce it 

 forwards, so that it shall just clear the driving axle, then let the 

 sides drop to within two feet of the rail, and close up the bottom. 

 Next, inside of this, place a rectangular box, which shall be a continu- 

 ation of the inner fire-box, the top being about 9 inches above the diam- 

 etric chord of the barrel, leaving a water space of 4 to 5 inches between 

 the sides and bottom of the boxes. Fill the inner box with vertical 

 tubes, the top and bottom being flue plates. The tubes being screwed 

 in at one end, and fitted with a screw thimble at the other, may be 

 removed for cleaning at any time, and wall effectually stay the inner 

 box against the immense pressure to which it is subjected. The pres- 

 sure, being inside of the tubes, will tend to keep the end joints tight, 

 where in the common boiler the reverse is the case. 



" That the gases may retain sufficient heat to burn until they are 

 discharged, there should be less tube surface to absorb the heat at the 

 back, than at the front end ; a requirement which is easily satisfied 

 by decreasing the number and increasing the size from the front to 

 the back end. In the common boiler the ferrule area being less than 

 the flue area, a stronger blast is required than is economical, because by 

 drawing hard enough to get the gases through the ferrules, we draw too 

 hard to carry them through the flues at a rate slow enough to admit of 

 a complete extraction of their heat. By means of the vertical flues we 

 may arrange the gas area in any way we please, making it larger at 

 the fire end, if necessary. 



" Again, any amount of oxygen may be applied to the gases at any 

 point of their passage from the furnace to the smoke box, by the ad- 

 mission of fresh air to any part of the barrel ; thus the advantage of 

 a combustion chamber (if there is any) is obtained without the sacri- 

 fice of a single inch of tube surface, as we are required only to admit 

 the air between the tubes, and not inside of them. This may be done 



