Section 4. The treasurer of each county shall annually pay for the support of law libraries therein such sums as may be appropriated therefor by the general court, and the county commissioners shall include in the estimates required to be filed under the provisions of section twenty-eight of chapter thirty-five such sums as they may recommend for such law libraries. Sums so appropriated shall be applied to the purchase of books and maintenance of libraries for the use of courts and of citizens. In counties having any law library association the county commissioners shall secure from such association recommendations as to the amount deemed necessary for such maintenance.