Flooring Tile - Adhesive Removal

I am wanting to install ceramic tile in an older house, the floor is concrete and had been previously tiled (possibly in 1950's) I have removed all of the tile and have begun TRYING to remove the adhesive. This adhesive looks like tar on the concrete, it is not a measurable depth. Do I have to completely remove the old adhesive before I can begin the new tile project?
It seems like the adhesive has actually soaked into the concrete, I am hoping that since the concrete itself is in good shape and the adhesive is so minimal, that I will be able to work over it.
Any help will be appreciated.

do you mean vinyl tile?If so and this was done in the 50's then you have old cut back that was ridden with asbestos my friend.What you need to do at this point is to encapsulate the remainder of this by getting some of a product called ardex feather finish and skim this floor.You do not want to disturb this stuff any further.

This is the only product i know of that mortar co.'s will back their products over could be more ,but this is the one i use all the time.Get back to us and let us know.:cool:

Thank you for your advise. I don't think the tile is vinyl, it reminds me of what they always put in the old schools. I guess it would be considered a ceramic. I love "fixer uppers" but this house is really testing my patience, thanks again