June 1, 1865.] THE TECHNOLOGIST. 



MINERAL SUBSTANCES FOR WRITING ON. 509 



sheets to make 1 in. in thickness : another sheet, 8 in. by 6 in., or 48 

 surface inches, weighed 25 grs. ; but, brought to the standard of 44 in., 

 gives but 23 grs., and requires 2,950 sheets to make 1 in. in thickness. 

 The Pontardawe Tinworks next come into the field with a sheet of 

 15| in. by 7 5-16ths, or a surface of 115-17 in., weighing 60 grs. ; 

 but, being reduced to 44 in., is 24^ grs. — a trifle heavier than the 

 Marshfield ; but Pontardawe claims 3,799 sheets to make 1 in. in 

 thickness. We now come to the climax. The mill manager of Messrs. 

 W. Hallam and Co., of the Upper Forest Tinworks, near Swansea, has 

 succeeded in making a sheet of the finest appearance and thinnest that 

 has ever yet been seen by mortal eye. The iron from which the sheet 

 was rolled was made on the premises. It was worked in a finery with 

 charcoal, and the usual blast ; afterwards taken to the hammer to be 

 formed into a regular flat bloom ; from thence conveyed to the balling- 

 furnace, and when sufficiently heated, taken to the rolls, lengthened, and 

 cut by shears into proper lengths, piled up, and transferred to the balling- 

 furnace again : when heated, it was passed through the rolls, back again 

 into the balling-furnace, and when duly brought to the proper pitch was 

 taken to the rolls, and made into a thorough good bar. Such is its 

 history in connection with the forge department. It was then taken to 

 the tin mills, and rolled and rolled till it was supposed to be thinner 

 than 23 grs., afterwards passed through the cold rolls to give it the 

 necessary polish, and now it stands on record as the thinnest sheet of 

 iron ever rolled. The sheet in question is 10 in. by 5^ in., or 55 in. in 

 surface, and weighs but 20 grs., which, being brought to the standard 

 of 8 in. by 5^ in., or 44 surface inches, is but 16 grs., or 30 per cent, 

 less than any previous effort, and requires at least 4,800 sheets to make 

 1 in. in thickness. That calculation is made in a rough way, without 

 any inch guage, but, if anything, is considerably under the mark. For 

 the curious, I will give them a calculation, which, if it does not give 

 them any instruction, may tend to amuse. A sheet of IC tin-plate 

 measures 10 in. by 14 in., or a surface of 140 in., and weighs ^ lb. A 

 box is made up of 225 sheets, but as many as 245 can be pressed in ; ~ 

 the depth of the box is 3| in. The latter number of sheets being taken 

 as our guide, we have 70 sheets to the inch. In order to make the 

 matter more clear, we will raise the 55 in. of 20 grs. to the ordinary 

 10 in. by 14 in., or 140 in., the weight being 50 10-1 lth grs. We now 

 find that | lb. avoirdupois contains 3,500 grs. troy weight ; we now 

 multiply 3,500 grs. by 70, the number. of sheets of IC thicknes to 1 in., 

 and -f- by 50 10-llths grs., being the weight of 140 in. of the thin sheet 

 in question, which gives us as answer 4,812^, that number, therefore, 

 being required to make 1 in. in thickness. I would just add that the 

 gravity of the iron in question, from which the thin sheet was rolled, 

 was from 7*8 to 7'9, and was not made in what is generally considered 

 the most superior — that is, hollow fires. The plan answers admirably 

 for tin-plates, and, in the present instance, fully corroborates that view 



