For some types of mixing, the reversal mixing vessel (see application sheet TN252) is not adapted : incompatibility of mercury with the samples, mixing of viscous substances. It is replaced by the mixing vessel with membrane. A membrane separates the two chambers eliminating the use of mercury. Mixing is performed by piercing the membrane by a rod which also acts as a stirrer (manual stirring). In the case of viscous substances or formation of a solid during the reaction, a continuous stirring is obtained by adapting a driven motor on the rod. When possible the reversal mixing vessel is preferred to the mixing vessel with membrane. It gives a better precision (no connection with outside).