Hi Andrea:

> Why do you boil them?

To make sure that there is no bacteria left alive on them - eggshells can be 
carriers of salmonella or other disease-causing bacteria.

Wouldn't the calcium be
> dissolved in the water as when you boil bones?

The shells appear to be intact - perhaps because the time involved is 
relatively short.

What do
> you grind them in? And how do you consume the powder?

I use a coffee grinder, pour the powder into a spoon and take it with some 
water to flush it down or I pour the powder over a spoonful of honey and eat 
that. Eggshell is fairly easy to chew and has a sort of sandy texture.

Marilyn