A smoke precipitator used in iodin analysis of food stuffs.

Abstract

Owing to high potentials needed for the Cottrell Precipitator, and the danger of short circuiting when manipulating the rest of the apparatus, it was decided to try another method of smoke precipitation in the combustion of large samples of food stuffs in the combustion tube, the smoke being passed through an alkaline solution to catch all the iodin. It is very difficult to catch the smoke in wash bottles, in fact it is stated that phosphorus pentoxid dust may be blown through a washbottle without complete precipitation. The method tried was as follows: The smoke was bubbled through distilled water, this somewhat cooling it and saturating it with moisture at 100°. Its further passage supersaturated it with moisture which caused each smoke particle to be surrounded by a layer of moisture. The precipitation apparatus was a glass tube 7 cm. in diameter and 45 cm. long, closed at one end by fusing the glass, closed at the other end with a rubber stopper, and provided with a side neck 1 1/2 cm. in diameter. By means of holes in the rubber stopper two block tin tubes 1 1/2 cm. in diameter were inserted. One of these tubes was open at the inner end and admitted the hot smoke which passed through the full length of the tin tube (keeping it hot), and then was admitted to the interior of the glass tube, and finally passed out the side neck. The other tin tube was closed at the inner end, and in it was inserted a 1/2 cm. tube admitting water and keeping it cool. The smoke in the glass tube was thus between a hot and cool tube. The smoke particles, on cooling sufficiently, were enclosed in droplets of water-vapor which were heated unequally by unequal radiation from the hot and cold tubes.