C 6; ] 



nearly compacted as the bottom of the cargo mud nc- 

 ceiTarily be, by the preiTure of the heap above) will 

 undoubtedly reach to the end of the pipes, and con- 

 fequently affect the cargo even there. 



Be it farther obferved, that the flux of air com- 

 prefled into an half-inch flream in its pafTage through 

 the nofle, to enable it to overcome the refiftance of 

 the fpiral fpring H, no fooner pafles the valve E 

 than it expands itfelf to the compafs of the pipe; 

 by which expanfion, and extenfion (at the fame time) 

 forwards, its power becomes fo weakened that fmall 

 egrefs only will be made till the pipes are filled with 

 a fluid more denfe than atmofpherick air, which will 

 then, as is jufl:ly noticed, iflue where it finds the leafl 

 obftruftion, unlefs attracted to the fpot mofl heated. 

 - Many circumfl:ances may caufe one part of the 

 cargo to be lefs permeable than the reft; fliould it 

 prove fo, the means readily offer for airing and pu- 

 rifying even this. 



Suppofe the hatches to be caulked down, and the 

 hold made impervious to water ; in fuch cafe the 

 Japfe of air under the obftruftions met with in its 

 pafl'age, could by no means keep pace with the influx 

 from the forcing pump ; confequently, if the holes 

 in the deck defigned for its exit, be kept clofe ftopt 

 till the pumper feels refiftance; all the intervals of 

 the cargo, be they ever fo minute or irregular, muft 

 be occupied by frefli air, which, when permitted to 

 cfcapc, will carry off impurities with it. J^nd thus, 



f 2 by 



