[' 342 J 



ing repeated, ibme air will come every time from the rec into 

 the barrel, 'till that in the rec' is as rare as the air in the barrel 

 would be, when the piflon is raifed to the top ; fuppofing no 

 communication to exift between the barrel and the rec", nor any 

 more air to be under the piTion when elevated to the top, than 

 there was when it was at the bottom. 



This pump adls likewife as a condenfing engine, without 

 any other additional apparatus than that common to all ; of a 

 frame for keeping down the rec', which in this fliould confift 

 of an iron bar to be laid under the frame fupporting the rec 

 plate ; in which bar are faftened two upright rods, with nuts 

 and fcrews at their ends, to f. revv down a crofs-piece prefling 

 down the rec' in the ufual manner. When the bar is thus 

 laid under the rec' plate, this latter will ftill be level ; for the 

 part of the iron frame of the machine which is under the 

 rec' plate, is higher than that part under the barrel by which 

 it is faftened with clamps to the table, as before defcribed ; 

 and when the frame of the condenfer is not ufed, a piecCj of 

 board fhould be laid under the reC plate to raife it to an ho- 

 rizontal pofition. 



The adlion of this pump in condenfing is as follows: The 

 cock of the gage-veflel is ftopt that it may not be burft ; the 

 valve is taken off; the communication of the bottom of the 



barrel 



