The apparatus shown in the figure for the determination of N-methyl group is a modified construction to overcome such difficulties as are produced by the apparatus of Pregl-Lieb, Friedrich and others in the course of repeated pyrolysis of samples for complete reaction.In consequence of the modification, the unreacted hydrogen iodide can be easily distilled off and condensed into the side-arm of the apparatus by means of a glass-sealed condenser; and thus, when necessary, the condensed acid can be made to return very conveniently to the reaction flask with the carbon dioxide stream ux, interrupted, simply by tilting the whole set by about 45° in the direction opposite to that of the distillation of the acid.This modification makes it easier to operate and to get better results.