IMPROVED CARD TO POCKET
In the 1920s Eddie McGuire wrote to T. Nelson Downs asking if he could buy some of his card secrets. Downs agreed to sell, and for an initial fee of $50, a considerable sum at that time, began a correspondence which extended over a decade and included many effects. The following was among them.
Thirty two cards handed to you and you openly deal them into two face down heaps, one card at a time to a heap, and step away. No palming. No extra cards. Two parties advance and pocket the heaps, and at your command two cards pass from one party's pocket and join those in the pocket of the other man. Simple and beautiful in effect.
There is a subtle variation in the dealing, which, when properly executed is indetectable if you patter and do not count as you deal. The first eight cards are dealt singly, one to each heap. Left thumb keeps the packet you are dealing from very slightly fanned. As you appear to deal the ninth card, you will find it very easy to deal two cards as one. The hand is in motion, and the fact is never suspected. Deposit the two on first heap, and without hesitating, right hand returns to pack and this time deals a single card onto second heap. then two together on first heap, and single card onto second. Then deal six singly, three to each heap. Then two to first heap, one to second. Two again to first heap and a single card to second. Continue to deal remainder of cards singly.
If you do not count as you deal, it is never observed that you do not make 32 separate dealing motions, and your patter keeps company from counting. First heap contains 18 cards, and second, 14. They will say each contains 16, when you inquire of them. The trick is done before they realize you've begun, hence it is difficult to detect.
The original description actually omitted one of the double deals. I've added that to clarify matters. It's one of the earliest uses of the double deal I have come across in a magic effect.