As a scholar of library science, Walter Lange conducted several bibliographical studies, while actively working as a rare text collector. For his Master of Arts degree, Lange wrote a dissertation on the French Revolution and the "lost Dauphin," the son of Louis XVI and Marie Antoinette, who was rumored to survive the French Revolution. Lange was also interested in the Wise Forgeries, concerning Thomas James Wise, a widely known book collector later turned out to be a forger. To investigate Wise's case, Lange exchanged correspondence with various scholars and collectors. One noteworthy part of the Lange collection is his own collection of the autographs related to the French Revolution. For several years, Lange conducted research on the rumor and the false claimants of the lost Dauphin, during which he created a collection of letters, hand-written documents, and notes of highly important figures, such as Karl Wilhelm Naudorff and Eleazar Williams, both widely known false claimants in the nineteenth century. His collection also encompasses first-hand records of the contemporaneity by French nobility and royal members, along with autographs and original letters of others who are less directly connected to the French royal family and the revolution. Besides the French Revolution, Lange's study on the Wise forgeries is also taking up a huge portion of the collection, although this part mainly consists of Lange's correspondence and book catalogues rather than firsthand texts. Lange also left a vast amount of book and autograph catalogues along with letters with other book collectors, which reflect his deep bibliographic interest in various types of rare texts.