Can you put ceramic tiles on old?

you have to remove the bathroom tiles .

No, the tiles must be removed and most times the Sheetrock also has to be removed. That's the easiest way.

You need to remove the old tiles.

Thank you both of you friends, but I was thinking if new ceramic tiles are glued on to old floor ceramic floor tiles then can also be put on walls ? Is it because it is difficult to fight gravity ..and that the tiles would just slide off before they are set ?

Not only the gravity but also the weight of the old and new can tear the wall and fall off.

You can paint the tiles with ceramics paint, if you are having sliding problem start at floor only do 2 rows at a time let dry then do 2 more rows

I think you're coming from a wrong assumption, or maybe you are mis-stating it in your question. But glue is not the proper adhesive to begin with. Anything can and will stay put on your wall when the correct adhesive is used on a properly prepped wall surface. I just asked this question at Home Depot regarding the use of reclaimed-wood look tiles for a guest bedroom feature wall. I hope this helps. But once you have the correct adhesive in hand you will probably find out that removing the present ceramic tile is the only way to get the correct surface on which to spread your adhesive and that there are no shortcuts! Like most things in home improvement what seems like a great idea always turns into a much bigger deal than what one expects at the start. Good luck.