While it bothered me that extra puzzles were kind glued on to the old game, Broken Sword Dir. Cut actually had ok puzzles with letters and decription and it was made for touch devices, check out the beginging of this clip:
(SPOILER WARNING) http://www.youtube.com/watch?v=cyBZmFoJc-8
And you can actually make it with various level of difficulty by revealing an element or two within the code or somewhere.
Although those solutions are for higher resolutions than you probably are prepearing, it still might be adaptable by a map-like (so you look at it and can move in certain direction to see the rest) overview of the periodic table. Then you can add some notes (like they began to correspond in codes so somebody wrote bits while trying to figure it out) on the sides of the Table so on the easier difficulty players have a hint.
(SPOILER WARNING) http://www.youtube.com/watch?v=cyBZmFoJc-8
And you can actually make it with various level of difficulty by revealing an element or two within the code or somewhere.
Although those solutions are for higher resolutions than you probably are prepearing, it still might be adaptable by a map-like (so you look at it and can move in certain direction to see the rest) overview of the periodic table. Then you can add some notes (like they began to correspond in codes so somebody wrote bits while trying to figure it out) on the sides of the Table so on the easier difficulty players have a hint.