Automatic Apparatus for Determination of Small Concentrations of Sulfur Dioxide in Air New Countercurrent Absorber for Rapid Recording of Low and High Concentrations MOYER D. THOMAS AND JAMES 0. M E , Department of Agricultural Research,
AND
T. CLEON FITT, Wertem Smelter Research
Department, American Smelting and Refining Company, Salt Lake City, Utah
A simple countercunent absorber i s described in which practically complete absorption of the water-roluble gaser such as sulfur dioxide, ammonia, and hydrogen chloride may be obtained with gas flow rates ranging from less than 10 to more than 5000 times the liquid rates. This absorber, when used in conjunction with a conductivity flow cell of small volume, gives a rapid recording of the concentration from a few parts per billion to several per cent. With the lower gas concentrations, the record is a running average, covering 1 to P minutes. A n alternative absorber containing conductivity electrodes can reduce this time to 10 to 15 seconds, but absorption is not complete. A simple pump for delivering small volumes of liquid is also described. Equipment embodying this absorber her been applied to the measurement of atmorpheric contamination, to the chemical control of a pilot plant making elemental sulfur from sulfur dioxide, and to the rapid measurement of rulfur dioxide in flue gases in the presence of carbon dioxide.
I
X T H E automatic apparatus for the determination of small concentrations of sulfur dioxide in air previously described (6-9), a uniform air stream is aspirated through a measured volume of absorbing solution for a definite time, after which the air stream is changed to a second absorber that has been automatically charged with fresh solution while the first absorber was aspirating. The sulfur dioxide is oxidized to sulfuric acid by hydrogen peroxide, and the course of the absorption is followed by measuring continuously the conductivity of the solution on a recording Wheatstone bridge. The record thus gives primarily the average gas concentration over a given time period, but it also shows a considerable part of the variability of the concentration during that period, represented by differences in the slope of the conductivity curve. It has been recognized that a more or less “instantaneous” method of recording the gas concentration would be advantageous in many applications, though the average values of short intervals (20to 30 minutes) are indispensable for any practicable summation of the record over long periods of time. Such instantaneous recordings have heretofore been precluded by lack of a suitable absorber to handle the large ratio of gas volume to liquid volume (about SO00 to 1) required for this analysis. APPARATUS
Figure
1. Diagram of Field Sulfur Dioxide Autometer
It is shown below that the indicated concentration a t any moment is an average value covering a period which may be as long as 1 or 2 minutes, following the lag representing the time required for the liquid to flow from the absorber to the cell. In an alternative, less efficient absorber, the total time for the analysis may be reduced to 10 to 15 seconds. Figure 1 is a diagram and Figure 2 is a photograph of an assembly designed to determine sulfur dioxide in the atmosphere in the concentration range up to about 3 to 5 p.p.m. with provision for automatically increasing this range severalfold if necessary. The absorber, A , is a 730-mm. length of glass tubing 7.6 to 7.8 mm. in inside diameter, with T-connections near each end. The tube is packed with a helix consisting of two strands of No. 26 B. & S. gage %
