On the Expenditure of heat in the Hot-air Engine. 225 
every pound of air receives an amount of heat which it does not 
afterward restore, sufficient to raise the temperature of a pound 
of water 20°97 F. Buta cylinder 22100 sq. inches base and 
72 inches altitude, will contain about 70 Ibs. of air of ordinary 
ensity. Hence, the unavoidable expenditure of heat at every m 
stroke of a hot air engine, having such a supply as well as work- 
ing cylinder, and working without bee will be =20°-97 x70 
applied to one pound of water = 14709, nearly. 
To convert water into steam at 212° Se at the usual es- 
timate, 11429. And sai ‘287 Ibs. According to Bourne’s 
tables, the mechanical effect of one cubic inch of water converted 
into steam at 212°, is equal to 2083 pounds raised one foot. And 
1-287 lbs. =35-58 cubic inches, similarly converted into steameat 
212°, are equivalent to 74100 pounds raised one foot, or 12075 
pounds raised through a six foot stroke. But we have seen in the 
article already mentioned, that the effect of a hot air engine, — 
supply and working cylinders equal, and pistons of 22100 
inches, is equal to 56400 Ibs. during the stroke. ae divans 
is in favor of the heated air, to the extent of 1:46 
If we take the properties of Ericsson’s i eae is, make 
the supply cylinder two-thirds of the working cylinder in capaci- 
ty, we shall have, provided we put the cut-off at two-thirds the 
stroke, for every ‘unit of weight of the air employed, the same 
number of units of heat, as before, at the moment of cut-off; but, 
in ros lt of the subsequent ies setian there will be an ad- 
Now, if the vlc eater is —_ of tak cog back the heat still uncons envedak 
end of the stroke, it is a benefit, though Captain rsa og cannot see it, to “turn the 
air adrift” at the er — ppt or, in other pecghacegy carry the maximum 
pressure to the and the comparison which presently follows 
the working cylinder, consists in the fact, that the effective power is absolutely 
expansively, But in Capt. Ericsson’s engines, the eed dity of a supply ie en to 
throughout nearly two-thirds of the stroke, oe working without cut-off; that 
a cut-off creates a negative ure at the close of the stroke, when me) mate engine 
is itself powerless or worse. The cu tie jee are removed by the plan recom- 
mended in another article of the present writer in this Journal. 
Lactiperrsiece Apasotetnit ecd aptain Eniesson is one of his own invention. He 
boa of heated air SS as if it were so much steam. And because steam can- 
be turned adrift wi it all its heat, 3 et 
ae and the purpore “for which they are intended oy mrp 
however, the moment we recognize his more radical theoretic error, : that the 
elastic force in air which is due to density, is something so ojalpendent of heat, 
Pe Soe epee SE any expenditure 
g at all, 
Soon Sasams, Vol XVI, No. 4%—Sept, 1858 29 
