Important: Safety Warning
This page contains a formula or preparation using substances now known to be dangerously toxic, such as arsenic, mercury, lead, or cyanide compounds. Exposure to these substances can cause severe poisoning, permanent injury, or death.
In addition, this page describes trade processes that use dangerously toxic materials such as cyanide solutions, mercury amalgams, or strong acids. These processes require training, equipment, and precautions far beyond what the text describes.
This information has been left in for historical purposes but should not be acted upon.
Hardening Metals
The processes for hardening or tempering the several metals are various. Steel is wonderfully affected by heating and then plunging into water, being so susceptible to this process that almost any degree of hardness may be obtained, and it may again be made soft and malleable, as before, by reheating and allowing it to slowly cool.
To harden cast iron, use a liquid made as follows: Soft water 10 gallons, salt 1 peck, oil of vitriol 1/2 pint, saltpetre 1/2 pound, prussiate of potash 1/4 pound, cyanide of potash 1/2 pound. Heat the cast iron cherry-red, and dip as usual, repeating the process if wanted harder.
Wrought iron is surface-hardened by heating to a bright red, sprinkling with prussiate of potash, and plunging into cold water when it has cooled to a very dull red. See METALS; TEMPERING.