The proteins separate on the
paper because some proteins are bigger and heavier than others. They are
not dragged as far by the water. Then, if you let the paper
dry, the separated proteins are just sitting there, and you can spray
a stain on them. The stain makes them appear like spots, each at a different
location along the paper.
this is a little crude, and better results can be had if you use an
electric current to help pull proteins apart. While the proteins
are migrating, an electric current can separate the proteins based
on their electrical charge. A more protein that has a negative
be pulled toward the positive source of current. An electropositive
protein would be pulled toward the negative source of current.
If a semi-solid substrate,
instead of water, is used, the substrate can be dried and stained
after the proteins are separated to reveal where each one is concentrated.
This is exactly the technique commonly used today. It is called
Gel Electrophoresis, because the substrate
is a Jell-O-like gel (semi-solid) that has microscopic pores that let
proteins migrate through.