The heat of sublimation actually has two components, the heat of solidification (actually melting, since this is going in the reverse direction) and the heat of vaporization since you are transforming the solid to a gas. The energy required is the same, even though you do not actually go through a macroscopic melting phase. So the sublimation energy will be much greater than the heat needed for just melting, given the same mass.
Sublimation is defined as the direct transition of a substance from solid state to gaseous state. The latent heat of sublimation is the sum of heat required for conversion from solid to liquid and heat required for conversion from liquid to gas. As in sublimation solid substance directly goes to gaseous state therefore, it is very difficult to find the components of latent heat of sublimation. This is the issue which arises in determining latent heat of sublimation.
On the other hand, when substance is melted it physically goes from solid to liquid. One can easily measure the heat required for this conversion.
The weight of the fluid displaced is equal to the buoyant force on a submerged object. The mass divided by the volume thus determined gives a measure of the average density of the object.
