Methadone Question

If I dump 6 100ml bottles of Methadone (each with 140mg of methadone) into a bottle and let them sit for awhile, am I safe to shake it really good and then dump them back into a 100ml bottle to get 140mg? or is there a chance it may not mix properly and end up with a much larger dosage?

I don't want to have to carry around 6 bottles with me every week, 1 large bottle and a way to measure 100ml would be much easier for me.