The permeability of cobalt, both annealed and unannealed, was always diminished at the low temperature.
A, B, C, D, E Annealed Cobalt..
Nickel and Annealed Cobalt.
In the construction of this soft-iron instrument it is essential that the fragment of iron should be as small and as well annealed as possible and not touched with tools after annealing; also it should be preferably not too elongated in shape so that it may not acquire permanent magnetization but that its magnetic condition may follow the changes of the current in the coil.
In some mints the fillets are annealed frequently, the fillets for one-mark pieces at the Berlin mint, for example, being annealed four times in the course of rolling.
A thoroughly well annealed ring of soft iron indeed showed no extension at all, beginning to contract, like nickel, under the smallest magnetizing forces.
In the walls and floor of the kiln special cooling channels or air passages are provided and by gradually opening these to atmospheric circulation the cooling is considerably accelerated while a very even distribution of temperature is obtained; by these means even the largest slabs can now be cooled in three or four days and are nevertheless sufficiently well annealed to be free from any serious internal stress.
Most of the permeability-temperature curves were more or less convex towards the axis of temperature, and in all the experiments except those with annealed iron and steel wire, the permeability was greatest at the lowest temperature.
This only requires to be annealed and is then ready for cutting up, but the lump of glass by which the original globe was attached to the pipe remains as the bullion in the centre of the disk of glass.
In the form of plate it can be tempered and annealed till its elasticity and toughness are much increased, and it can then be formed into almost any shape under the hammer and punch.