DH.. HOPMANN'S COMPOUND TESTING JET. VII.-Campoz&nd Testing Jet. BY A. W. HOFMABNN, Ph.D. F.C.S. The very extensive and daily increasing application of gas as a source of heat in chemical experiments has suggested to me a small contrivance which is intended to facilitate the operations of the analyst. The ordinary Argand gas-burner which is almost universally employed for heating small vessels such as flasks retorts and test-tubes is not adapted to the purposes of the blow-pipe. In opera-tions with the latter instrument a simple jet of gas is required .j.a DR. HOFMANN'S COMPOUND TESTING JET. issuing from a cylindrical orifice of rather considerable dimensions the necessary amount of gas being adjusted by the stop-cock. This simplest of all gas-flames serves equally well for oxidation and reduc- tion and exhibits the phenomena of colour in the most conspicuous manner.The ordinary method of analysis being a combination of testing in the moist way and by the blow-pipe it is necessary either to use two gas-lamps-the one with the Argand burner the other with the single jet-or to have a gas-stand so arranged as to admit of screw-ing on either the one or the other. Rut as it is inconvenient to multiply the number of gas-lamps especially in a laboratory in which several analytical students are working and as unscrewing hot gas- jets is a most unpleasant operation I have endeavoured to unite the two jets in one stand dispensing at the same time with the necessity of taking the apparatus to pieces.The object in view is accomplished simply by substituting for t,he ordinary stop-cock a three-way cock. The whole arrangement be-comes at once intelligible by a; glance at the wood-cut which represents the burner half-size. A is'the loaded' foot into which the elbow-union-piece B is screwed. One end of this union is connected with a flexi- ble pipe? not shown in the draw- ing; to the other screws the three-way stop-cock C. The plug .V has only one orifice and when turned in a vertical di- rection supplies the Argand-burner through the perforation E. Into the side of the stop- cock is soldered a small pipe F having a bore of about Q of an inch. This is prolonged to the distance of Tb of an inch above the top of the Argand burner where it is brazed to a small support for the blow-pipe not represented in the drawing.Wlien the plug D is turned DR. KOLBE ON THE ORGANIC RADICALS. in a horizontal direction the gas is shut off from both jets but when turned in an inclined position may be made to supply both jets at once or either alternately. By this contrivance either of the jets will be lighted before the other is extinguished. In order that the jet may be likewise used for heating larger apparatus there is a support G on which may be fixed a copper chimney either plain or provided with the wire-gauze for producing the air-flame. The above burner has been made under the superintendence of Mr. J. J. Griffin whose assistance I thankfully acknowledge.