AMERICAN INSTITUTE. 583 



effective to ebaWe steam of anything like the proper pressure to be used, 

 only 2.933 lbs. of combustible, or 3.317 lbs,, of coal, per hour, were required 

 to develop a horse-power. But to come to the real practical point at 

 issue — the cost in full, per effective horse-power, for it matters not what 

 the developed horse-power may be, if it cannot be developed into useful 

 effect, but is partially used up in its own development — five pounds per 

 square inch of initial steam pressure is sufficient, without any load upon 

 the engine, to draw it at the speed at which it was worked on the 2d of 

 May, which is less than five per cent of that which was used ; and, there- 

 fore, we require but 3.08 lbs. of combustible, or 3.49 lbs. of coal, per 

 hour, per effective horse-power, which is less than half the ordinary con- 

 sumption of marine engines. 



To oblige Mr. F. in regard to the "San Jacinto:" The consumption of 

 fuel, under its best boiler, was 3.565 lbs. of combustible, or 4.827 lbs. of 

 coal, per hour, per developed horse-power j or, 4.505 lbs. of combustible 

 or 6.100 lbs. of coal, per hour, per effective horse-power, allowing 2 of the 

 9.58 lbs, of the mean gross effective pressure on the piston, for working 

 the air pump, and overcoming the friction of the engine, without any load. 

 But I have not yet done ; for when the boiler is two or three 3'ears old, its 

 evaporative effect will be so far reduced as to require, probably, 6 lbs. of 

 combustible, or 8 lbs. of coal, per hour, per effective horse-power; for the 

 ordinary rate of evaporation, under such circumstances, scarcely exceeds 

 on the average, more than 6 lbs. of water, with 1 lb. of coal ; while my 

 boiler, (" only the size of a large stove," as Mr, Isherwood says,) ever 

 remains as good and effective an evaporator as when new. 



Again, ordinary boilers of sea-going steamers usually wear out in five 

 years, while mine will, in all probability, last an age. Remember how- 

 ever, that this boiler is but a mere incident, not at all necessarily connected 

 with my system of applying and condensing steam. It is through the 

 medium of this new system, that the economy and perfect safety of the 

 boiler depends. It gives to the condenser a large surface, with a small 

 capacity, in proportion to the contents of the boiler ; hence, if the feed- 

 pump should cease to act, the condenser becomes choked up with the water 

 which should be in the boiler, and the engine is brought up lono- before 

 the latter is in any danger, from deficiency of water. Thus, safety is 

 insured. Economy in fuel is the sure result of distilled water at a high 

 temperature, alone being supplied to the boiler. 



I hope, ere long, to see another volume (3,) of " Engineering Prece- 

 dents," from Mr. Isherwood, — one on surface condensers, — when, I am 

 sure, we shall have facts elicited such as the engineering world is, at present, 

 lamentably deficient of. 



There are some points in- Mr. Isherwood's remarks on my boiler with 

 which I do not agree, and believe I can convince him of the correctness 

 of my own views, should occasion arise to make it necessary or desirable. 



For the present I will merely observe, that his statement of the absence 

 of any combustion chamber in my boiler is a very singular and unaccount- 



