[TheForge] Mercury quench

[Shannell Sugrue]

Im reading a book called "The one best way" about the life of Frederick
Taylor, hes the guy who started the time and motion studies and setup the
modern efficient way of manufacturing etc, good book, good part devoted to
his apprenticeships as machinist and pattern maker, in this section he
mentions quenching drill bits in mercury instead of water as a way of making
them harder, Ive never heard of this, can anyone tell me why this would be
so, I know it boils a lot higher than water so there wouldnt be the same
steam jacket around the metal like water has but is that all there is to it?