H
Harry Hoosier
Something about roasting egg shells and apple cider vinegar.....
Is this what you are thinking of?
Mix 1 part crushed oyster shells (or egg shells) with 3 parts apple cider vinegar and let it steep for 2 - 3 weeks.
The vinegar will extract the calcium from the shells in a concentrated form. Mix 1/4 cup of the vinegar with 1 gallon of water and apply to your soil.
And you can heat the shells in the oven until black and brown and then crush. Distill them in the same manner as above for calcium phosphate.