This section is from the book "Safe Building", by Louis De Coppet Berg. Also available from Amazon: Code Check: An Illustrated Guide to Building a Safe House.
For rolling or mill work the most used are the Nos. 2 and 3, Grey Forge and Mottled of the mill irons. For castings the most used are the Nos. 1, 2 and 3 and Grey Forge of foundry irons; the Mottled and White being usually sold for cheap mill-work.
For steel the iron should be as free as possible from phosphorus and sulphur, and the same, so far as possible, for rolled-iron. The presence of these makes iron fluid and soft and good for fine castings, but unfits it for rolling or forging.
Irons for mill and steel work are usually much stronger than for foundry work.
Scotch irons are used in castings to make the melted iron more fluid, to soften it; but they greatly weaken the casting. For very fine castings, Coltness is the best and softest. For ordinary architectural castings, such as columns, lintels, etc., either Giengarnock or Eglinton (both Scotch irons) can be used ; using one-third Scotch to two-thirds of some good American iron; using Nos. 1 and 2 of the latter in equal proportions.
Sloss (American) iron is now frequently used by good manufacturers as a softener in place of Scotch iron.
For good and yet strong castings, use Thomas, Crane, Copley, Manhattan, Low Moor, Glendon or Coleraine. Add Sloss or Scotch for extra fine castings. Or add Glendon, Secausus or Castle for extra strong castings, using the No. 1 mill irons for the strongest work.
For rolled iron-work use Glendon, Andover, Taylor, Thomas, Stanhope, Adlentown, Cornwall or Bethlehem. The latter two being used for steel.
In every case the better qualities (Nos. 1 and 2) will, of course, give the best results.