text: Platinum is extremely dense (heavy for its size).  Not only will it not float in water, it will sink faster than lead!  Its extremely difficult to measure the size of a small ring using the water test-I know, Ive tried it and I have access to a laboratory.  Platimun, like gold, is resistant to normal acids.  If your ring resists corrosion from hydrochloric or sulphuric acid, its platinum.