Here is a follow up to my statement about the coal torpedo. I found it at the Today in Hisotry website. It has been offically discounted as Terry says, but I remember reading about it several years ago and I will paste a portion of the report I read earlier.
"Investigations into the cause of the explosion concluded that low water levels in the ship’s four boilers were to blame. Since the ship was severely overweight on this trip, she tended to list more when making turns. Water from one boiler would spill into another and then back; when the water returned to the near-empty boiler, it would flash to steam and cause a spike in pressure. Eventually, one of the boilers could no longer contain the force of the steam and exploded.

Another, much more controversial theory was put forth in 1888 for the cause of the explosion. It was claimed that Robert Louden, on his deathbed, had admitted to placing a coal torpedo in the bunker onboard the steamboat. A coal torpedo was essentially an explosive device camouflaged to look like an ordinary piece of coal. When exposed to fire, it would heat up and explode, sometimes causing boilers to rupture. Louden was a former Confederate agent embittered by the south’s recent defeat in the Civil War. Also, the man who invented the coal torpedo, Thomas Courtenay, had lived in St. Louis during the time Louden was there. However, despite the confession and the potential for collusion between Louden and Courtenay, no physical evidence was ever found to support this theory."
FC