"Mercuric fulminate, HgC2N2O2 ... (is) almost insoluble in cold water and requiring 130 times it weight of boiling water for solution. It may be heated to 180° C. before exploding, and the explosion so brought about is much milder than that produced by percussion."
NOTE: Water boils at 100° C.
http://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Explosives