Anyone hear of soaking an egg shell in lemon juice overnight to make a high calcium tonic? I remember reading something about this but can't remember where. I seem to recall that the acid in the lemon juice will leach out the calcium carbonate from the shell. Any thoughts as to if this is plausible and if so, how much calcium would one shell yield??? Yes, I have heard this too. In fact, I was just thinking about this the other day although I do not know how much calcium it would yield. It seems it would depend upon how much calcium was in the shell in the first place, as that will probably vary depending on how and what the chicken was fed. If you are going to try it remember to wash your eggs first, as it is the outside of the shell where salmonella bacteria is.