Abstract: A viscous fluid reaction apparatus is described. The viscous fluid reaction apparatus comprises a glass reaction vessel. The viscous fluid reaction apparatus further comprises a gas-tight inlet assembly and a gas-tight stirrer assembly. The gas-tight stirrer assembly comprises a stirrer opening adapter, a stirrer coupling comprising a stirrer shaft seal connected to the stirrer opening adapter, a stirrer shaft comprising one or more stirrer blades located at a blade end of the stirrer shaft, and a motor coupling connected to the stirrer shaft. The viscous fluid reaction apparatus further comprises a motor connected to the motor coupling. The stirrer shaft passes through the stirrer coupling and the stirrer opening adapter such that the stirrer blade(s) are disposed in the glass reaction vessel at a blade height and the stirrer shaft is configured to rotate without compromising a gas-tight seal formed by the stirrer shaft seal.