Deferiptm if a new Atr-pump', $o^ 



muft be lubricated, and made air-tight by ointment * ; and as all oil or greafy ointment ha». 

 an acid in jt (of which, perhaps, it can never be divefted without deftroying its lubricity) 

 which corrodes the brafs, and ftifFens the oil or ointment itfelf, by impregnating it with 

 green ruft or verdegris, I found it neceff"ary>. after the cock was finifhed> to have the key. 

 and the infide of the (hell eoated with tin. 



The key of the cock terminates in a littk knob k, fig. 2. againft which the end of the 

 tliin fpring lever y prefles to keep the key conftantly firm in its fhcU : this fpring is made 

 to urge onward the key, with any degree of force requlfite, by the fcrew at y, fcrewcd 

 through the outer part of the little arch, or frame, which frame is itfelf faftened by fcrews 

 on the prominent ring of the barrel, as appears at z, fig. 2. The lever has a little ridge, 

 or elevated part, which refts in a notch in the frame ; by which the lever is fixed in its 

 proper place, the notch being the fulcrum : by withdrawing the fcrew the ridge may be 

 raifed out of the notch, and the lever pulled back from the knob, to let the key be taken out 

 when it requires more ointment ; which will be known when it has worked into the fliell 

 nearly to its limit ; and this fliould be carefully learned, by marking how far it can be in— 

 ferted into the (liell without any ointment intcrpofed. The form of the key, and its lever, 

 is exhibited in fig. 6. in an horizontal fedlion through the middle of them; 



Through the fliell of this cock are two round perforations for two dufts, through the; 

 cock, each one inch diftant from the other, and the fame from the end of the cock on either- 

 fide : they are in a plane^ or fe£tion, paffing through the axis of the key, and alfo through 

 the axis- of the barrel ; and bothpafs through the ridge of metal T at the back of the fliell. 

 The du£t irext the fmaller end of the key (being a part of the du£l communicating with the 

 receiver) is in diameter :^th, and the other dufl: is only ^th of an inch : through the key, alfo^ 

 are du£ts aniwcring to the perforations in the (hell ; but the du£ts in the key are not both' 

 in the fame fedion of it, but oneef them is at right angles to the other ; fb that whsn one- 

 of the dufts through the cock is open, the other will be always fiiut, and vice verjd. 



There is a continuation of each of thofe da£Vs formed in the piece of metal V, which i* 

 joined (by cement interpofed) to the ridge of the fliell. of the cock by the four fcrews g, gt 

 fig. I. by two openings (into the two dufts in the piece of metal) oppofite to thofe in the. 

 ridge ; and thefe dufls in the piece V have two other orifices at a, and r, where the two- 

 pipes- a i, fig I. and c d^ fig. 2- communicate with the two canals in the piece of metal, 

 being conneded with them only by the help of cement, that the barrel with its cock may be 

 occafionaliy disjoined from them : thus- a feparate ccmimunication is formed between each' 

 of the pipes, and the barrel. 



The pipe a b isonly rVth of an^inch in diameter, except at its orifices, which are widened; 



'■* This I have- made of one part of common rofin, one part oil, and one part and a half frefh fuct : the oil. 

 and rofin is firft melted, and when a little cooled the fuet is added, that the heat requifue to melt the rofia 

 may not burn the fibrous part of the fuet, and dearoy its firmnefs : more oil is to be added in cold, than in 

 warm weather. The quality of the ointment for thecock is of the utmoft confequence ; for if ever the parts 

 of the metal of the cock came into immediate contaa, it will not be air-faft- oil will not render it fo (not 

 wnfequently would a valve) ; but the ointment muft be ftiff and adhefive ; yet not too ftiff, as then k would ■ 

 bf hard to turn the key, and it could not be diftinguiflied whether its ftiffneft was owing to the ointment,. or. 

 to theiriaion o£ the parts of the metal getting into iromediau contad, wliich would be pernicious.— L. 



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