Any cooperative association or corporation organized under the laws of this Commonwealth, or under the laws of the United States, or qualifying as a cooperative association under the laws of the United States, may give as security for any loan or loans obtained from any bank for cooperatives organized under any act of Congress a chattel mortgage or deed of trust covering stocks of goods or other things in bulk, but changing in specifics, in which case the lien of such mortgage or deed of trust shall be lost as to all articles disposed of by the mortgagor up to the time of foreclosure but shall attach to the articles purchased to supply their places; provided, however, no stock of goods shall be pledged by a cooperative association unless such stock has been fully paid for and is owned by the association without incumbrance at the time it is so pledged.