Nitroglycerine is commonly described as the tri-nitric ether of glyceryl, and the formula C3H5(O.NO2)3 is accorded to it. This theory of its composition is based (1) upon its mode of formation; (2) upon the statement, made by Railton, Williamson, and others, that it is decomposed by potash into potassium nitrate and glycerine; (3) upon several estimations of the nitrogen which it contains, and one comparative estimation of its carbon. The second argument cannot be accepted, as it has been shown by one of us that the decomposition does not take place in the way stated; and the analytical results which have been obtained by the various investigators are so incomplete and mostly so imperfect, and differ so greatly among themselves, that they cannot be taken as affording any proof of the composition of the substance. It seemed to us, therefore, desirable that some accurate estimations should be obtained, not only of the nitrogen but of the carbon and hydrogen. A brief résume of previous analytical results will show that this is the case.