[ 59 ] 



the fame time fufficiently contradled to prevent the 

 paflage of the fpiral fpring. 



Fig. 5. Is an affemblage of tin pipes of any lengths, 

 fhaped fuitably and conveniently to their fituation in 

 the fliip ; to the form of which, when {hut into one 

 another, they muft be adapted ; obferving only that 

 the neck be ftraight for a length fufficient to admit 

 the lower end of the cylinder fig. 4, as high as the 

 letter F. or higher. 



Fig, 6. To the middle pipe which runs along the 

 bottom* fhould be fixed a perpendicular one, fully 

 perforated, to convey the air more readily into the 

 centre of the heap, and this may have a conical top, 

 as reprefented in the plate, perforated with a fmaller 

 punch to prevent the air from efcaping too haftily. 

 In large cargoes, two or three of thefe perpendiculars 

 may be neceflary, and each fliould be \^ell fecured 

 by an iron bar g. fcrewed down to prevent their be- 

 ing injured by the fliifting of the. cargo in ftormy 

 weather or a rolling fea. The top of the conical cap 

 of thefe pipes may reach two-thirds up the cargo. 



Fig. 7. Is a valve of the fame conflruftion as 

 that reprefented in fig. 4, but inclofed in a tube of 

 brafs, having a female fcrew at//, adapted to the 

 male fcrew cc. on the nofle fig. 2, and may then 

 be inferted into the head of the pipe fig. 5. This 

 will add to the expence, but in a large apparatus is 

 to be preferred as a more certain fecurity from lapfe 



of 



