This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
Procure two cards, the "5" of diamonds and the "3" of spades, for example. Bend each exactly in the center, with the face of the cards in, and then paste any card on the back, with its face against the two ends of the bent cards. The two opposite ends will then have their backs together. and these are also pasted. The illustration clearly shows this arrangement.
To perform the trick pick up this card, which is placed in the pack beforehand, and show to the audience both the front and back of the card, being sure to keep the center part flat against one end or the other, then pass the hand over the card, and in doing so catch the center part and turn it over. The card can be changed back again in the same manner. - Contributed by R. Bennett, Pittsburgh, Pa.
Ill: A Card Having Two Faces, Either of Which can be Shown to the Audience Instantly