150 Account of ihe 



grease while the tin is in a melting, or at least in a soft, stale 

 upon it, a part must run off, and the remainder become less and 

 less while the plate continues in it ; therefore, if these plates 

 should ever be left in the melted tallow longer than is abso- 

 lutely necessary, they will doubtless require to be dipped a third 

 time in the tin. On the other hand, if the plates were to be 

 finished without passing through the grease, they would retain 

 too much of the tin, which would be a loss to the manufacturer, 

 and besides, the whole of the tin would appear to be in waves 

 upon the iron. 



It is also equally necessary to attend to the temperature of the 

 melted tallow, which must be colder or hotter in proportion as 

 the plates are thicker or thinner ; for if, when the tallow is of 

 a proper temperature for a thin plate, a thick one was to be put 

 into it, it would come out, not of the colour of tin as it ought to 

 be, but as yellow as gold. The reason of this is evident. The 

 thick plate contains more heat than a thin one, and consequently 

 requires the tallow to be at a lower temperature. On the 

 contrary, if a parcel of thin plates were to be worked in a 

 pot of tallow which had been prepared for thick plates, such 

 a pot would not be hot enough to effect the intended purpose. 



It is a common observation that, in most of our manufactures, 

 and in all chemical speculations, theory and practice are gene- 

 rally at variance; but there are few manufactures, perhaps, 

 where there are so many minutiae which would escape the notice 

 of a casual observer, and yet that require to be carefully attended 

 to, in order to produce a good result, as in that which we have 

 now been describing — and should the perusal of this paper oc- 

 casion but one individual to pause, who was about to enter into 

 a new concern with which he was only partially acquainted, I 

 shall have written to a good purpose. 



But to return to the process. When the plates are sufficiently 

 brtished, they are again immersed, one by one, in the pot of 

 melted tin, as has already been remarked, and immediately from 

 this they are put into the pot of tallow above-mentioned. This 

 pot has pins fixed within it, in such a manner as to prevent the 

 plates from touchingcach other ; arnl this part of the process is 

 conducted in the following manner : 



