In the book Giant Book of Card Tricks by Bob Longe there is a trick called Oily Water. The object is to separate the black cards from the red cards. No matter how many times I try I always get one card in the wrong pile. Please someone tell me what I am doing wrong.
Here are the exact words from the book without all the patter

• four red cards four black cards. arrange them so they alternate black and red.
• Turn packet face down. Move top card to bottom of the packet.
• Turn packet face up fan out the cards.
• Move two cards to the bottom of the packet one at a time. Turn packet face up and fan out the cards they still alternate colors.
• Lift off two cards from the top hold them to one side so all can see that there are two and place them together on bottom of the packet.
• Take off five cards dealing them one at a time and one on top of the other. Place this bunch on bottom of the packet. Show the packet face up.
• Turn packet face down. Take off four cards one at a time one on top of the other. Fan out the cards so can see they are alternate colors. Place this bunch face down on bottom of the packet. Turn packet face down. Take off the top two cards together and place them face down onto the table at your left. Move two cards one at a time from the top to the bottom.Take off the top two cards and place them on table to the right. Move one card from the top to bottom. Take off top two cards together place them face down on table to the right. Drop last pair on the left.

I follow this but I get one different color card in a pile instead of all the same color cards in the pile. Please help.
Thanks.