TINNING, PLATING, &C. 309 



should be once well established, that ships sheathed with lead or 

 copper will not last so long as those which are unsheathed, or sheath, 

 ed only with wood, it would be a problem well deserving the con. 

 sideration of chemists, to inquire into the manner how a metallic 

 covering operates in injuring the construction of the ships, and 

 whether that operation is exerted on the iron bolts, or on the tim. 

 bers of the ship. When the iron plates have been cither ham- 

 mered or rolled to a proper thickness, they are steeped in an acid 

 liquor, which is produced from the fermentation of barley meal, 

 though any other weak acid would answer the purpose; this steep* 

 ing, and a subsequent scouring, cleans the surface of the iron from 

 every speck of rust or blackness, the least of which would hinder 

 the tin from sticking to the iron, since no metal will combine itself 

 with any earth, and rust is the earth of iron. After the plates 

 have been made quite bright, they are put into an iron pot filled 

 with melted tin ; the surface of the melted tin is kept covered with 

 suet or pitch, or some fat substance, to prevent it from being cal. 

 cined ; the tin presently unites itself to the iron, covering each side 

 of every plate with a thin white coat : the plates are then taken 

 oot of the melted tin ; and undergoing some further operations, 

 which render them more neat and saleable, but are not essential to 

 the purpose of tinning them, they are packed up in boxes, and are 

 every where to be met wilh in commerce under the name of tin- 

 plates, though the principal part of their substance is iron ; and 

 hence the French have called them for blanc, or white iron : Sir 

 John Pettus says, that they were with us vulgarly called lat ten ; 

 though that word more usually I think denoted brass. 



Tin is not, but iron is, liable to contract rust by exposure to air 

 and moisture, and hence the chief use of tinning iron is to hinder it 

 from becoming rusty j and it is a question of some importance, 

 whether iron of a greater thickness than the plates we have been 

 speaking of, might not be advantageously tinned. I desired a 

 workman to break off the end of a pair of pincers, which had been 

 long used in taking the plates out of the melted tin ; the iron of 

 the pincers seemed to have been penetrated through it's whole sub- 

 stance by the tin ; it was of a white colour, and had preserved it's 

 malleability. It is usual to cover iron stirrups, buckles, and bri- 

 dle bits, with a coat of tin, by dipping them after they are made, 

 ioto melted tin ; and pins, which are made of copper wire, are 



