Chemical Preparations and Drugs. 53 



which it is possible to burn the benzaldehyde with a non-sooting flame by supplying 

 air, we have replaced the flask by a vertical glass cylinder through which we draw 

 a current of air which is free from hydrochloric acid. 



We have found a suitable medium for the absorption of the hydrochloric acid, 

 resulting from the combustion of the chlorine compounds, in a very diluted potash 

 lye, of which a sufficient quantity is placed into the first absorption vessel, of the 

 apparatus, a U-tube charged with glass beads. The second absorption vessel which 

 contains the same amount of caustic lye, but is charged with glass beads only in the 

 one limb, enables us to control whether the total amount of hydrochloric acid has 

 been retained in the first absorption vessel. There is further a test tube, partly filled 

 with water and provided with a suction nozzle, for the purpose of making a qualitative 

 test of the abscence of hydrochloric acid in the drawn-off gases of combustion. 



The annexed diagram will explain the construction of the apparatus 1 ). We should 

 state that only the U-tubes E and F are clamped, both to the same stand, by the two 

 limbs which are next to one another, whilst the combustion cylinder D and the sphere G 

 find sufficient support by their stoppers. 



The most important part of the apparatus is the lamp A, in which the material 

 is burnt and which is mounted on a flask of a capacity of about 20 cc. The neck 

 of the flask is provided with two ground-glass joints, the one on the outside for the 

 cap B which is put on when a weighing is to be made, and the other on the inside. 

 There a glass tube, slightly thicker at its lower end, is ground into the neck. Into 

 this tube fits a small tube of porcelain which is likewise thickened just below its 

 upper end. This porcelain tube which has an internal diameter of 2 mm. carries the 

 asbestos thread A which serves as a wick. On the upper portion of the glass tube 

 fits a short sleeve of metal threaded on the outside; the sleeve is pushed over the 

 thickened portion of the glass on which it sits firmly. The three-arm spider for the 

 semispherical globe which is fitted with an aperture of 6 mm. turns easily on the 

 threaded sleeve. 



Before we proceed to a quantitative determination the respective benzaldehyde is 

 first tested qualitatively for its chlorine contents 2 ) in order to obtain some indication 

 of the quantity of material to be burnt in the test. The apparatus is then fixed up 

 for the quantitative estimation in the following way: — 



The two limbs of the tube E are charged with glass beads to about three quarters 

 of their length, and 25 cc. of N/50 caustic potash are introduced through the upper 

 opening, into which the cylinder D is afterwards fixed, so that the beads of the limb 

 are wetted with the potash. The one limb of the U-tube F is then similarly charged 

 with glass beads and with the same amount of caustic potash. Both the U-tubes are 

 now clamped in their upper portions and are closed by their rubber stoppers. The 

 test tube H is charged with about 10 cc. of water and joined to the sphere G which 

 is fixed in position on the top of the tube F; H is then connected with the water 

 jet pump. Finally the combustion cylinder D is joined to the U-tube E, and the 

 lamp holder is preliminarily fixed by means of its holder C and. the stopper pushed 

 over C. As the air of the laboratory might contain some vapours of hydrochloric 

 acid, the holder C is connected with a washbottle containing diluted silver nitrate; 

 the water jet pump is started at a rate that about 1 litre of air is drawn through 

 the apparatus a minute. 



*) The apparatus can be obtained from F. Hugershoff in Leipzig. — 2 ) Gildemeister and Hoffmann, 

 The Volatile Oils, vol. I, p. 609, and Report October 1904, 8. 



