Kraft pulping experiments were performed in a 12-L electrically heated laboratory digester to determine pulp yields and residual lignin content (kappa number) as a function of time. Samples of the pulp and the black liquor were analyzed for total organic carbon (TOC) content by oxidizing the samples in a combustion furnace and measuring the released CO₂ gravimetrically. The experimental data on TOC were correlated with kappa number and yield. Results can be explained satisfactorily using a mathematical model based upon the principle of conservation of mass. The TOC content of black liquor appears to be a useful parameter for batch digester control. -- AATA