Expansion of hollow bodiesDo hollow and solid bodies made of the same material have the same expansion when heated even when they have the same external dimension?
No. The hollow area will not expand at the same rate as the other material. For instance, if it were an air pocket, the expansion will be huge when heat is applied. At the same time, if a gas fills the hollow area, it will expand according to it atomic weight and properties.
If the liquids are the same, then the volumes are additive. You just have more of the same liquid. However, if they are two different liquids the volume may not be additive. One liquid might dissolve into the other, and you might have the same or slightly more.