852 Traxsactions of the American Institute. 



of the vessel, apply the heat, and a column of steam will flash up 

 to the ceiling, and you will evaporate more water thus in a few 

 seconds than in as many minutes in the former case. You will say 

 that the steam formed at the bottom promotes circulation in the 

 boiler; that is true, but it is equally true that if the water were not 

 there, circulation Avould not be necessary. 



You may plug up the lower half of the tubes in a boiler, and 

 then make as much steam as before. An engineer recently stated 

 on this floor that he had tried this experiment on a locomotive, and 

 after closing one hundred of its one hundred and sixty tubes, made 

 more steam than before. This is perfectly philosophical, for the 

 heat which had before passed through the lower tubes, and was 

 converted into mechanical motion in the boiler, is now driven to 

 the top, and utilized as steam. Hence we will wipe out the lower 

 half of this boiler as being a little worse than useless. 



It is well known that flame cannot enter a tube of less size than 

 the body of the flame itself, because, when the air is excluded from 

 its surface, combustion ceases. It is also well known that hot air 

 or gas imparts caloric principally by contact, and in its rapid pass- 

 age only the outside stratum of air touches the tube, hence little of 

 the heat is absorbed, and as a consequence, we find that the first 

 few inches of a boiler tube make more steam than all the remainder, 

 whatever may be its length. So we will dispense with the greater 

 part of these upper tubes as being nearly worthless, leaving only 

 a few inches of them, together with the crown sheet; and here we 

 have the part of the boiler which makes nearly all the useful steam. 

 Bat unfortunately this part is too far from the fire, as you can see, 

 to be of much service, so we will wipe it all out, as not a single 

 inch was under circumstances where a maximum evaporation could 

 follow; and probably more than fifty per cent of the little actual 

 evaporation exerted its full equivalent of work in the boiler with- 

 out ever reaching the engine. What wonder, then, that we only 

 utilize ten or twelve per cent of duty from the fuel. 



It beinjr evident that flame or hot air cannot be used to advantajye 

 in conveying caloric from the furnace to the distant parts of the 

 boiler, we must look for some better medium; and it is in steam 

 itself we find the very elements of success. This may, at first, 

 appear paradoxical, but I am convinced that if we are ever suc- 

 cessful, it will be in this direction. There is no other medium so 

 well adapted for transmitting heat. The cylinders of a large 

 marine engine, measuring a thousand cubic feet, will discharge their 



