I had ran across this lately and thought some might be interested. This is not the exact formula that I had seen before but maybe it is worth a try. Most of the owner/builders do not have the resources for a mechanical means to extract stumps so this may be a good alternative.

Get rid of tree stumps by drilling holes in the stump and filling them with 100% Epsom salt. Follow with water, and wait. Live stumps may take as long as a month to decay, and start to decompose all by themselves.