Anna Feigenbaum provides a brief history of tear gas. Her bottom line:

In the 100 years since it was first developed, tear gas, advertised as a harmless substance, has often proven fatal, asphyxiating children and adults, causing miscarriages, and injuring many. The human-rights organization Amnesty International has listed tear gas as part of the international trade in tools of torture, and Turkey’s medical association has condemned it.

Yet while tear gas remains banned from warfare under the Chemical Weapons Convention, its use in civilian policing grows. Tear gas remains as effective today at demoralizing and dispersing crowds as it was a century ago, turning the street from a place of protest into toxic chaos. It clogs the air, the one communication channel that even the most powerless can use to voice their grievances.

In this way, tear gas offers the police a cheap solution for social unrest. But rather than resolve tensions, it deepens them. This week in Ferguson, police fired tear gas into people’s backyards, set it off near children, and launched it directly at journalists.