What am I?
1. I am about 15 centimeters long, made of brass and I am the shape of a sphinx.
2. I sat on desks from the 1890s and well into the 1900s.
3. I was filled with a dark liquid.
4. My sphinx-like head is hinged to give access to the inside.  
5. I probably won't be used for the same purpose now, especially if a ballpoint lies nearby.

Last week's answer? I am an exercise club.  People would swing me to keep fit.