Anyone who has ever been to a halfway-decent pool or used bleach for cleaning knows the characteristic smell of element number 17. Less conspicuously, chlorine is also found in NaCl; a.k.a. ordinary table salt. Rather than pursue a compound, though, I went straight for the good (if not slightly scary) stuff.
Embedded in this acrylic cylinder is a small quartz ampule containing pure chlorine. While chlorine is normally a toxic, corrosive, evil gas at room temperature, the high pressure inside this ampule (approximately 7 bar) is sufficient to condense it into a toxic, corrosive, evil liquid. Luckily, the small amount of chlorine, the strength of the ampule, and the thickness of the acrylic make this sample very safe to possess.