340 TUBULAR BOILER, SUPERHEATING STEAM, 



condensing the steam in its passage without any of its oxygen 

 being burnt, it will not carry off so much heat from the fire 

 as cold air would, and still have the same oxygen as cold air 

 to consume the coal. 



" The cold air will b3 passing down the steam-case in the 

 air-tubes, and up through the fire and fire-tubes in the boiler. 

 I find by experiments I have made here, by placing a tin 

 tube 2J inches in diameter, 4 feet long, inside a 4-inch tube 

 of the same length, having boiling water and steam between 

 the tubes, kept hot by a fire round the outer tube, with a 

 smith's bellows blowing in at the bottom of the inside tube, 

 having 2|rds surface feet of condensing sides, measuring the 

 inside, where the air is passing up from the bellows, heats from 

 60 to 134 degrees 15 square feet of cold air per minute. 

 When you compare the effective heat of 74 degrees given to 

 15 cubic feet of air every minute from 2f rds surface feet of 

 tin plate, and the heat contained in 15 cubic feet of air 

 charged with 74 degrees of effective heat, compared with steam 

 of atmosphere strong, you will find that the condensing power 

 of surface sides is very great, and for locomotive purposes 

 might be carried still further, by forcing the air more quickly 

 through the tubes. If the statements on air given in some 

 books that I have read are correct, that there is about three 

 times as much heat in 1 gallon of steam of atmosphere strong 

 as there is in 1 gallon of air of 212 degrees of heat, in that case 

 1 surface foot of tin-plate sides of this pipe, by sending off the 

 hot air before described, would take out the heat of 1J cubic 

 foot of steam per minute of atmosphere strong, which in the 

 common condensing engine would be equal to a duty of 

 2700 Ibs. lifted 1 foot high per minute ; but in the high- 

 pressure expansive engine, the heat of 1J cubic foot of steam 

 would give a duty of 10,800 Ibs., or four times the duty of the 

 Boulton and Watt engine. 



" If you calculate on the air being heated to nearly 212 degrees 

 before it enters the fire, together with the heat given to the 

 sides of the boiler, the fuel saved will bs above one-half on 

 what has been done by the high-pressure engines in Cornwall, 

 because at present the coal must pay for heating the cold air, 



