Microdetermination of Halogen by Combustion An Absorption Apparatus L. T. HALLETT, Eastman Kodah Co., Hochester. S . 1.
first be opened. The stopper, B , is loosened from its seat without actually removing it from the funnel, and 30 ml. of distilled water are poured in 5-ml. portions into the funnel. What fraction of the wash liquid will flow into by-pass D and down the section of the tube containing the helix is determined by the rate of addition of the water. The entrance to chamber E may be partly closed with stopper B and more of the wash water will thus be deflected into the by-pass. As a general rule both sections of the absorption tube~-i. e., chamber E and the helix-should be completely and simultaneously rinsed.
T
HE regular Pregl method for the determination of
halogen and sulfur consists in burning the sample in a combustion tube with oxygen and passing the combustion gases over a spiral which is placed in the end of the tube and is moistened with a suitable absorbing solution. When the sample has been burned, the tube is allowed to cool, the absorbed products are rinsed out with distilled water, and the tube is washed with acetone and then dried by the passage of a stream of air. Cooling, rinsing, and drying require 5 to 7 minutes each, and where routine determinations are carried on day after day, this expenditure of time is appreciable. While the amount of actual working time during the combustion was reduced by the introduction of the elect r i c f u r n a c e f o r automatic combustion ( I ) , the total working time was reduced to a desirable minimum by a new design of the absorption part of the tube which facilitates the introduction and removal of the absorbing solution, permits the products absorbed to be removed immediately after combusC tion, and eliminates the necessity for drying the combustion tube afterwards. Thus, the total time required for the performance of a halogen determination was shortened by 10 to 15 minutes.
The absorption tube just described was designed especially for the absorption of iodine. The iodine is mainly absorbed on the glass filling of E which is moistened with sodium carbonate solution. This part of the apparatus ib kept warm enough by the heat from the furnace so that all of the iodine sublimes into the s o d i u m carbonate and is absorbed. G a s e o u 5 products, such as hydrogen chloride and hydrogen bromide, are also completely absorbed on the way along the glass helix. Although the apparatus was designed primarily for halogens, it may be used for the absorption of other gases by using suitable solutions. For reasons of econoniy, a glass rather than a quartz stopcock was used a t the outlet of the absorption tube and was attached by means of a tubing of pure r u b b e r . The whole absorption tube could be made of hard glass and a ground joint might be used for the connection to the quartz combustion tube. Hon-ever, this is not recommended for the absorption of the iodine, because the outlet of the combustion tube and the inlet of the absorption apparatus must be kept fairly warm. Freezing of the joint is likely to occur and the warm part of the glass apparatus is liable to crack if wash water is spilled on it, O n t h e o t h e r hand, with an apparatus made completely of quartz, it is a relatively simple matter to cut off the absorber and to seal i t to another combustion tube whenever necessary.
1
D
Apparatus The absor tion apparatus consists of a clear fuse!-quartz tube sealed on t o the combustion tube, A (Figure 1). One to 2 ml. of the absorbing solution are added by means of a pipet, the point of which is inserted through the funnel, C, and brought down to a level approximately 5 mm. above the filling of the small chamber, E. This prevents creeping or spattering of the absorbing solution into tube L4 and its failure to be removed when the absorbing products are rinsed into the receiver. The glas stopper, B , is then inserted and sealed by introducing a few drops of water into the funnel, C. The stopcock at the outlet of the absorption tube is, of course, kept closed during the introduction of the absorbent as well as during the combustion. The flon- of gas through the apparatus causes the absorbing solution to rise around the helix and keep it moist at all times. The combustion gases enter the small absorption chamber, E, which is filled TTith short pieces of curved Pyrex glass rod or with Pyrex glass beads 3 t o 4 mm. in diameter. The short pieces of glass rod are obtained by cutting a helix of the dimensions as used in the absorption tube into pieces 1 cm. long and firepolishing the sharp edges. On leaving E , the combustion gases are led down through the narrow tube, F , ascend along the glass helix, and leave through the bypass, D, and the funnel, C. To collect the absorbed products in a flask or beaker, the stopcock must
F
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SCALE-CM
Literature Cited (1) H a l l e t t , L. T., IND.ENG. CHEX.,Anal. Ed., 30, 101 (1935).
FIQURE 1.
APP.4RATV.3
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RECEIVEDNovember 2 2 , 1 9 3 i . Cornmunication 653 from t h e Kodak Research Laboratories. The apparatus was briefly described before t h e Microchemical Sertion at t h e 94th 3Ieeting of t h e American Chemical Society, Rochester, K. T.,September 6 to 10, 1937, i n connection with t h e paper "An Electric Organic Combustion Furnnce for the Automatic Burning of the Sample."
