It's perlite. Comes in the soil.
If it's not perlite, the reason I'm wrong is that you have given no useful information about the 'things' other than that they are 'ittle' and 'white'. Perhaps they are grains of rice. Or hummingbird eggs. Or very small rocks (which apparently float, by the way, ask Terry Jones aka Sir Bedevere).
You really need to do some basic reading.