Section 51. All goods, supplies, equipment and services, except for legislative or military purposes, needed by the various executive and administrative departments and for other activities of the commonwealth shall be purchased by or under the direction of the operational services division in the manner set forth in section fifty-two, and in sections twenty-two to twenty-six, inclusive, of chapter seven. Said division shall be furnished with such general supply appropriations, in addition to its departmental supply accounts, as may be necessary in order to place blanket contracts or advance orders and thereby take advantage of favorable market conditions.