Briggs] 230 t^*y- 



work of a 36 h. p. engine. These calculations show that the force 

 of the fly-wheel is only available for the exigency of part of a minute, 

 and not as a store of force in working out a heat. 



Admitting that we cannot rely upon the making of steam on the 

 instant of rolling, as sufficient for working out the heat (even when 

 we consider the waste-heat of your four furnaces to be employed in the 

 formation at the time of rolling), what is the next source of force? 



The following figures will demonstrate that the quantity of heated 

 water in the boilers must supply the deficiency. 



Suppose the blow-off point of the boilers to be 85 lbs., suppose 

 the minimum working pressure of steam (to insure the proper acce- 

 leration of the fly-wheel between the passes) to be 60 lbs., then I 

 estimate (somewhat approximately) as follows : 



Pressure. Temperature. Volume of steam per Weight of cub. ft. of 



lb. of water. water at 318°. 



85 328° 4.2 cub. ft. 



60 307° 5.8 '' " 



56.7 lbs. 



56.7 lbs. at 21° = 1191°, div. by lat. heat of water at 60 lbs. 



~900° 



Giving lySg-jjths lbs. of water transformed to steam (or 7 J cub. ft. of 

 60 lbs. steam made) out of each cub. ft. of water in the boiler. 



Suppose the governor to regulate so that 60 lbs. is the highest 

 pressure which enters the cylinder, then each cub. ft. of steam the 

 boilers may hold at 85 lbs. will have supplied || = 1.38- cub. ft. of 

 steam to the engine. Showing that as a store of power, water con- 

 tents are about five times as valuable as steam contents in the 

 boilers. 



The above indicates the ground on which is based the EngHsh 

 practice of elephant boilers; and aside from the consideration of 

 safety from abundance of water, and of ease of getting at the inte- 

 rior, to remove scale or sediment, it still further demonstrates the 

 propriety of the objection I urged, to the abstraction of water-space 

 by flues or tubes, in rolling-mill practice. .... 



Secondly. To get the largest result (for combustion of coal under 

 boilers), there is used, in tubular boilers of the best type, 3 feet of 

 surface for each pound of coal burnt per hour. 



For mill practice, with cylinder boilers, about 18 feet of surface 

 per square foot of grate is used. 



If I had but few furnaces, I should prefer to increase this to about 

 24 feet of surface (or even 30) per square foot of grate. This is 



