815 
for Preserving Corn on Ship-board, 
air (notwithstanding the manifold perforations, obstructed 
as it is in meandering through a mass so nearly compact- 
ed as the bottom of the cargo must necessarily be by the 
pressure of the heap above,) will undoubtedly reach to 
the end of the pipes, and consequently affect the cargo 
even there. 
Be it further observed, that the flux of air compressed 
into an half-inch stream, in its passage through the nosle, 
to enable it to overcome the resistance of the spiral spring 
H, no sooner passes the valve E, than it expands itself to 
the compass of the pipe ; by which expansion, and ex- 
tension (at the same time) forwards, its power becomes 
so weakened, that small egress only will be made, till 
the pipes are filled with a fluid more dense than atmos- 
pheric air, which will then, as is justly noticed, issue 
where it finds the least obstruction, unless attracted to the 
spot most heated. 
Many circumstances may cause one part of the cargo 
to be less permeable than the rest; should it prove so, 
the means readily offer for airing and purifying even this. 
Suppose the hatches to be caulked down, and the hold 
made impervious to water ; in such case, the lapse of air, 
under the obstructions met with in its passage, could by 
no means keep pace with the influx from the forcing- 
pump ; consequently, if the holes in the deck, designed 
for its exit, be kept close- stopped till the pumper feels 
resistance, all the intervals of the cargo, be they ever so 
Then, a single discharge of the forcing pump being eight gal- 
lons, five such discharges amount to 40 gallons, which is more than 
equal to the contents of 6 feet of four-inch pipe. 
And as on the larger scale of ventilators the pipes need not ex- 
ceed the same diameter, the power of the air injected, when its 
egress is stopt, will increase sufficiently to force its way through 
webs, mats, and other obstructions, though impervious to the atmos- 
pheric fluid, unassisted by such mechanic aid. 
