Plastic Reaction Vessel Ralph Kaszerman Corporate Chemical Research Center, Allied Chemical Corporation, Morristown, N.J. 07960
Difficulties are frequently encountered when determining the precise assay of fuming acids. Losses may occur from volatilization during the transfer of the weighed sample, and from spattering when introducing the acid into water or into a known volume of standard sodium hydroxide. With the use of this apparatus, these errors are eliminated. The apparatus can be assembled in several minutes from parts that are readily available at low cost. The weighing bottle (A. H. Thomas Catalog No. 9869-F23) is made of polypropylene and the reaction vessel is a conventional 16-02. wide mouth polyethylene bottle (or any other suitable size). With a cork borer, a hole is made in the cap of the weighing bottle and in the bottle cover. A short length of polyethylene or PTFE rod fits tightly into both holes and provides an air tight seal. In conventional use, the empty weighing bottle and cap with attached rod are weighed. The fuming acid to be analyzed is cooled (to minimize loss from volatility during transfer) and a suitable amount is transferred rapidly to the weighing bottle. The weighing bottle is tightly stoppered and reweighed to determine sample weight. A known volume of standard sodium hydroxide solution in excess of the amount required to react with the acid is transferred to the polyethylene bottle. The top of the rod is now inserted through the hole of the large bottle cap. The cap on the weighing bottle is loosened slightly but not sufficiently to cause sample loss. The bottle cap is then screwed on tightly. By means of a sharp tap on a table top, the weighing bottle is dislodged from the cap and drops with the sample into the sodium hydroxide solution. Because the apparatus is sealed, no losses will occur and the bottle can be mixed to ensure complete reaction of acid and sodium hydroxide. The contents are transferred to a beaker and the excess sodium hydroxide is titrated with standard acid solution. The all-plastic apparatus is particularly suitable for the analysis of strong solutions of hydrofluoric acid. For other acids that may attack polypropylene, the weighing bottle and rod can be made of PTFE. Construction by machining the weighing bottle cap and rod as one piece would eliminate the possibility of sample loss due to an improperly fitted rod.
Figure 1. Plastic impact reaction vessel
Although originally designed for the analysis of acids, this apparatus can probably be used successfully for other applications where it is desired to react a sample and receiving solution without loss in a sealed enclosure. According to the description of the polypropylene weighing bottle in the A. H. Thomas catalog, the “tendency to accumulate a static charge may prevent use for certain applications”. We have not found this to be a problem when used as described.
RECEIVEDfor review September 2,1976. Accepted September 13, 1976.
CORRECTION
Bipolar Averaging Circuit for Enhancing Signal-to-Noise Ratios in Recorded Spectra
In Figure 1 of this article by J. A. Wehrly, J. F. Williams, D. M. Jameson, and D. A. Kolb, Anal. Chem., 48,1424 (1976), the clear line (Cl) of flip-flop 2 (FF2) should be connected to the Y output of data select 5 (DS5).
ANALYTICAL CHEMISTRY, VOL. 48, NO. 14, DECEMBER 1976
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