In our second memoir on fired gunpowder we have discussed in detail that part of M. Berthelot’s friendly criticism of our first memoir which relates to the potassium hyposulphite found by us, in variable proportions, in our analyses of the solid products obtained by the explosion of gunpowder in the manner described. While pointing out that we had taken every precaution in our power to guard against the production of hyposulphite, by atmospheric action upon the potassium sulphide, during the removal of the hard masses of solid products from the explosion vessel, and had effectually excluded air from them, when once they were removed until they were submitted to analysis, we admitted the impossibility of guarding against the accidental formation of some hyposulphite during the process of removal, especially in some instances in which the structure of the residue had certainly been favourable to atmospheric action, and in which a more or less considerable development of heat had afforded indications of the occurrence of oxidation. We contended, however, that the method of analysis, and the precautions adopted by us in carrying it out, precluded the possibility of accidental formation of hyposulphite at this stage of our investigations. With respect to the precautions, we could, and still do, speak with perfect confidence; and we certainly have believed ourselves fully justified in being equally confident with respect to the process adopted by us for the determination of the proportions of sulphide and hyposulphite, inasmuch as we accepted and used in its integrity the method published in 1857 by Bunsen and Schischkoff in their classical memoir on the products of explosion of gunpowder, and adopted since that time by several other investigators who have made the explosion of gunpowder the subject of study, and whose results are referred to in our first memoir.