A further point about particles can be illustrated by looking at what happens when salt is added to water. To begin with, the salt is visible as a heap at the bottom. But then:
Of course, it hasn't disappeared, it has dissolved to create a solution, with salt as the solute and water as the solvent. We can test this by tasting the water. It will taste salty.
The key point here is that the salt particles spreading through the water are invisible to us. In other words: