[ 33^ ] 



The key of the cock terminates in a little knob v, £g. t. 

 againft which the end of the thin fpring levei^ v, prefTes to 

 keep the key conftantly firm in its fhell : this fpring is made 

 to urge onward the key with any degree of force requifite, by 

 the fcrew at y, fcrewed through the outer part of the Uttle 

 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 re- 

 quires more ointment ; which will be known when it has 

 worked into the fhell nearly to its limit; and. this fhould be 



T t 2. carefully 



fo, I rubbed the parts to be tinned very well for half an hour, or more, with a. 

 linen rag wetted with diftilled vinegar, in which had been boiled fome falam- 

 raoniac, together witk an amalgam of quickfilver and tin ; 'till the metal was 

 every where well coated with the amalgam ; then wiping off the loofe particles, 

 I heated the metal in the fire, 'till in the dark, it was juft beginning to appear 

 red hot ; with this heat the mercury evaporated, leaving a very hard coat of tin 

 on the metal, without in the leaft injuring its (liape or polilh ; this alfo pre- 

 vented the key and fhcU of the cock from tearing one another by friftion, which 

 would certainly fpoil th.> cock, as frequently happens with foft brafs. 



The iiifide of the b\rr-l (for reafons hereafter given) fhould be tinned in the fame 

 manner ; but it fliould, before- it is at firft pohfhed, be heated equally red in the 

 fire, and fuffered to cool equally and gradually, that it may not alter its fhape 

 when heated again in tinning. Any other method of tinning it, but thisj would 

 be both dilRcult and hazardoui.- 



