Limestone is quarried at Buxton, Millersdale and Matlock for lime, fluxing and chemical purposes.
Sodium and potassium carbonates are valuable for fluxing off silica; mixed with potassium nitrate sodium carbonate forms a valuable oxidizing fusion mixture; "black flux" is a reducing flux composed of finely divided carbon and potassium carbonate, and formed by deflagrating a mixture of argol with 4 to 2 its weight of nitre.
A large fire-grate (ab), having a cave (c) to facilitate stoking and stepped back at (d), is bounded on one side by a fire-bridge (e); on the other side of this, separated by an air-channel (g), there is first the proper fluxing bed (h), and behind this the "back-bed "(i) for pre-heating the charge.
It sometimes contains as much as 7 0% of carbonate of lime; but generally the amount is much less and the fluxing value proportionally diminished.
The crystals of octahedral borax fuse more easily than those of the prismatic form and are less liable to split when heated, so that they are preferable for soldering or fluxing.
