The Missing Formula - Mildred A. Wirt Benson

Orphan Anne Fairaday faces a life of poverty upon the death of her father. The only thing that can prevent it is finding his latest experiment. She enlisted her new found friend, Madge Sterling, an outdoors girl who has a knack for finding missing things. But they must race against time as there are also several people who will stop at nothing to get it first. (Summary by Mary Escano)