How does a drop salt spreader work?

In the same way as a generic or agricultural drop spreader and rather like a broadcast spreader, the material starts in a hopper.

As the spreader moves forward,  the material is released by gravity and vibration through a row of holes and, unlike a broadcast spreader, drops straight down to the ground.  

The distribution is measured so an even drop is achieved.

 

A Tow Behind Drop Spreader

N.B. In any type of salt spreader, the spreading material (salt, grit) should always be free flowing and dry.