An add-on batch delivery system for measuring heats of reaction of milligram amounts of solids, liquids and gases with less than 1 mL of liquid in a Calorimetry Sciences Corporation model 4200 calorimeter is described. The system was tested with reactions of dry N-2 gas with H2O, HCl(aq) with aqueous tris(hydroxytnethyl)atninotnethane (tris), KCI(s) with H2O, tris(s) with HCl(aq), Zn(s) with HCl(aq), 2-propanol with H2O, and CO2(g) with NaOH(aq). The precision and accuracy of a single heat measurement is 2-3 mJ or 1-2%, whichever is larger. (c) 2006 Elsevier B.V. All rights reserved.