Section 2. The volumes purchased, as aforesaid, shall be distributed as follows: One copy to the office of the Secretary of the Commonwealth, one to the office of the Adjutant General, one to the library of each college in the State, one to each historical society in the State, one to each public library in the State that has a free distribution of its books, one to the Library of Congress, and one to the library of each State and Territory of the Union; the balance to be placed in the State Library of Pennsylvania, for the purpose of exchange.