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of the piece of metal to the cock, as alfo of the duds to that 

 piece of metal, are made air-tight by melted cement interpofcd 

 between them *. 



The 



• The parts to be joined were firft made very clean and bright, and then heated fo 

 much as to melt the cement quite fluid ; fome of it being thus fmeared on the whole 

 of the furfaces which were to be applied together, before they were joined ; as 

 otherwife it would not penetrate into an extenfive joint, efpecially if the metal were 

 too cold, for the cement would grow folid in its paflage ; nor would it intimately 

 cohere with either glafs or metal lefs hot. The cement I ufed for this purpofc was 

 made of about two parts of common refin and one part bees-wax, melted together, 

 which anfwered well enough : this I alfo melted, with an iron moderately hot, round 

 the edges of the rec' on the plate, both being previoully warmed; when I wanted the 

 rec'' to be permanently air-faft, or when from its fides being too weak or of an im- 

 proper (hape, there was danger that being exhaufled, its fides might change their 

 form by the great preflure of the external air, in which cafe fofter cement would, by 

 yielding, admit air. 



Whenever it is necelTary to open the barrel to clean it, the pifton is to be firfl 

 raifed to the top, the nut to be then unfcrewed from the end of the pifton rod, the 

 arm of the rack to be taken off, and the fcrews faftening the box of leathers to the 

 end of the pump, to be taken out ; then with a hot iron, or rather a candle and blow 

 pipe, melt the cement joining the circulating-pipe to the piece of metal attached to 

 the box, (or unfcrew them if joined by a fcrew.) The box of leathers may then be 

 taken off, and the pifton extracted, which, with the barrel, &c. being cleaned, 

 the parts may be replaced without disjoining any other part of the pump. N. B. 

 The leathers of the pifton having been at firft treated as before direfted, freth hog's- 

 lard would be beft to lubricate its edges with, afterwards ; foi if oil were ufed for this 

 purpofe (at leaft copioufly) fome of it would get into the holes of the cock, and 

 making the ointment of it too foft, it would admit air. Alfo after ointment has 

 been put on the cock, and the key has been often turned to fpread it evenly, the 

 key, before the pump is worked, miift be taken out ; and the mouths of the dufls in 

 it, cleared of the oiiitment by a pin, and alio of thofe in the fliell, by a crooked wire. 

 This is neceiTary to any pump conftrucfled with a cock in place of a vaK-e. 



