Among the numerous apparatus that have been devised for determining the power of powder, those designed for military purposes are the ones most extensively used. Up to the present, very few experimental apparatus have been constructed for civil uses, although such are no less necessary than the others. Mr. D'O. Guttman has examined the principal types of dynamometers with respect to their use for testing explosive materials, and, after ascertaining wherein they are defective, has devised an apparatus in which the principle is the same as that employed by Messrs. Montluisant and Reffye at Meudon, that is to say, one in which the force of the powder is made to act upon a lead cylinder fixed in a conical channel. Mr. Desortiaux objects that in this system, when it is employed with charges for cannons, the action has already begun when only a portion of the powder is burned. To this, Mr. Guttman responds that his apparatus operates only with small charges (300 grains), which practically inflame simultaneously in every part when the igniting is done in a closed space. In order that the force may not be made to act in one direction only, the inventor uses two leaden cylinders. His apparatus is shown in the accompanying Figs. 1, 2, and 3. It consists of a median piece, a, and of two heads, b, of an external diameter of four inches. These pieces are of tempered Bessemer steel. The two heads are four inches in length, one inch of which is provided with a screw thread. Each of them contains an aperture, c, 1.34 inches wide below, 1.3 inches wide above, and 1.18 inches deep. This aperture is followed by another and conical one, d, 1.38 inches deep, and 0.4 inch wide at its narrowest end, and finally by another one, e, 0.4 inch wide, which runs to the exterior. The median piece, a, is 4 inches long. It is provided at the two sides with nuts, between which there is a cylindrical space, f, 1.8 inches long, designed to receive the charge. The inflaming plug, g, is screwed into the exact center of the median piece, a, which it enters to a depth of one inch. Into the space that still remains free is screwed a plug, h. The lower surface of the plug, g, contains a hollow space, 0.6 inch wide and deep. This hollow is prolonged by another one, 0.24 inch wide, and contains a valve, i, which has a play of about 0.08 inch. The three parts are connected by a key which passes into the holes, x, and are rendered tight by copper rings, y.