146 Accoitut of the 



called (jraiii tin is smelted from an ore which ia found in grains 

 called stream tin ore, under beds of alluvial soil, in low situations, 

 whither in the course of ages, it has been washed from the hills 

 by a succession of torrents of rain. The former, which is pro- 

 duced in the greatest abundance, is always contaminated with a 

 portion of iron, sulphur, and other injurious substances, and is 

 therefore only employed for common purposes — while the grain 

 tin, which is nearly free from every impurity, and usually from 

 twenty to thirty shillings per hundred weight dearer, is used in 

 the processes of dyeing, and in all other cases where pure tin is 

 required. I am also desirous of remarking, that, in my opinion, 

 it would be more profitable to the proprietor of a tin-plate work, 

 if he were to use grain tin alone, or grain tin mixed with that 

 kind which is known by the name of " Refined Tin," because 

 these kinds not only contain less dross, but they melt, as I know 

 by my own experience, into a more fluid metal ; and conse- 

 quently, more would run oft the plates in the operation of tinning, 

 and less tin would be consumed. At present these manufacturers 

 use the block and grain tin, in equal proportions. 



When the tin-pot has been charged in the way above men- 

 tioned, the metal is heated from a fire-place underneath it, and 

 by flues which go round the pot, until it is as hot as it can be 

 made without actually inflaming the grease which swims upon its 

 surface. The use of the grease is to preserve the tin from the 

 action of the atmosphere, and consequently to prevent it from 

 oxidating. By melting a little tin or lead in an iron ladle, .and, 

 when the dross is skimmed off, putting a morsel of tallow upon 

 the metallic fluid, the effect of the tallow in cleansing the face of 

 the metal will be evident. The workmen also say, that it in- 

 creases the affinity of the iron for the tin, or, as they express it, 

 that it makes the iron plates take the tin better. 



It is curious that burnt grease, or any kind of empyreumatic 

 fat, effects this purpose better than pure fresh tallow. 



Another pot, which is fixed by the side of the tin-pot, is filled 

 with grease only ; and in this the prepared plates are immersed, 

 one by one, before they are treated with the tin ; and when the 

 pot 18 filled with them, they are suffered to remain in it so long 



