Out Of This Century

The magician shows a deck of cards face and back. He takes a small group of cards and spread them on the table, face up, to show they are alternated red-black-red-black etc., one by one in color.

The rest of the deck is shuffled by the spectator and the cut into two portions which are placed by the magician each one to each side on the table. 

The magician collects the cards he had spread before and, by a magical gesture, he spread them back to show that the red a clack cards have inexplicably separated. 

He now takes the two packs (that had been shuffled) and when he spreads them, we find in one of them all the red ones and in the other all the black ones.

Completly automatic!