This is a 4572 Mabie Todd Swan Eyedropper in black hard rubber from around 1910. This comes with some interesting design elements such as the original hard rubber plug underfeed with a gold overfeed and medium italic 14k gold nib.
Cap imprints are very crisp whereas section & barrel imprints are quite worn and hard to read. This comes in an original red Swan Repair box - c1910
This is an eyedropper filling pen which is of interest for its design features. We would not expect it to be used other than perhaps while kept on a desk