For those interested, the MSDS says Kasenit is 46% Sodium Ferrocyanide, Na4 Fe(CN)6.
It also contains carbon black.
http://hazard.com/msds/f2/bdb/bdbls.html
Sodium Ferrocyanide is also known as yellow prussiate of soda.
Despite the presence of cyanide, Sodium Ferrocyanide is not terribly toxic in small amounts and it is used in common table and road salt to prevent caking.
The MSDS recommends using Kasenit in a well ventilated area which is probably recommended to be on the safe side.
Interestingly, the MSDS does not give the warning that is mentioned in Wikipedia, that information source saying that the cyanide is tightly bonded to the sodium but cautions that if it is mixed with an acid, cyanide gas will be released.
(In other words, do NOT mix any acids into Kasenit unless you want to create your own gas chamber).
http://en.wikipedia.org/wiki/Sodium_ferrocyanide
I've used Kasenit for a number of years and it does work very well and it is easy to use.
I often use it to harden the slotted screw heads on my rifles.
The case depth it creates is VERY THIN so don't expect it to last a long time if it is used on a frizzen for hardening.