This is an antique bronze "Payson's Patent" sash lock with a patent date of August 25, 1885. 

Patented January 4, 1876. From the patent papers:

To all whom it may concern: Be it known that I, JoSEPH. R. PAYSON, of Chicago, in the county of Cook and State of Illinois, have invented a new and useful Improvement in Window-Sash Lock, of which the following is a specification: Figure 1 is a top view of my improved sash lock, shown as attached to the sash and un fastened. Fig. 2 is the same view as Fig. 1, but showing the lock fastened. Fig. 3 is a side view of the same, the meeting-rails being shown in section through the line aca, Fig. 2. Similar letters of reference indicate corresponding parts. . The object of this invention is to furnish all improved sash-lock to be attached to the meeting-rails of the sash, which shall be simple and inexpensive in construction, conveniently operated, safe in use, and without springs or other parts liable to break or get out of order. The invention consists in the peculiarly shaped locking-arm, in combination with the plate and its flange; in the locking arm and hook, in combination with the plate and its flange, and with the plate and its pin; and in a sash-lock in which the locking-arm is pivotel at or nearly at an angle of forty-five degrees with the length of the meeting-rails of the sash, as hereinafter fully described.