AIDS FOR THE ANALYST Absorption-Titration Flask for Determination of Sulfur in Steel Milton Roth and Seymour Lader, Generol Laboratory Section, Picatinny Arsenal, Dover, N. J.
[Holler, A., Klinkenberg, R., Friedman, C., R Aites, W. K., ANAL.CHEM., 1658 (1954)] there v a s described a combined method for the determination of sulfur and ECENTLY
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reservoir by means of the double stopcock arrangement. The tip of the buret is inserted into the flask and the sample is titrated mvhile the gas is absorbed in the hydrochloric acid solution. Three determinations can be conducted in the same solution and then the vessel drained by means of a stopcock provided for that purpose. This apparatus has been in use for the past 3 years and has been found convenient and time-saving.
carbon in steel. The gases from the combustion of the ferrous metals in oxygen are passed through a suitable train, so that sulfur dioxide is dissolved in an acid solution contained in an absorption-titration flask, and the carbon dioxide is absorbed by Ascarite. Although an absorption-titration flask assembly is commercially available, it is relatively expensive and the source of supply is limited. -4suitable flask can readily be fabricated from the following pieces of glassware. Quantity
Description
1
Three-necked flask 24/40 necks, 500-ml. capacity Three-way stopcock with double oblique bore Inner connection with sealed-through tube, 24/40 Connecting tube with 24/40 inner joint
2 1
1
By relatively simple g1:tss Iiloning, these items are nswnihled as shown in the diagram. The bubbling tube is made from a piece of glass tubing and is attached to the inner connection as shown. The bubbling tube serves to diffuse the combustion gases throughout the sulfui dioxide-absorbing solution. A conventional fritted-glass diffusion tube was found unmtisfactory for obtaining a suitable gaseous flow rate. The operation of the flask is simple and efficient. The required reagents for the iodometric determination of sulfui are hydrochloric acid for absorption of sulfur dioxide, starch indicator, and standard potassium iodate solution (Ani. Soc. Testing Materials, “Methods of Chemical Analysis of Metals,” p. 129. 1950). The acid and indicator are admitted to the flask fioni a
A U ~ E Tme STANDAED
PUBBEE
It1
+GAS
INLET
Results Obtained with Apparatus 6BF
Standard Sample S o . 9d l5d 16e 20d
Carbon, % Xominal Found 0.20 0.21 0.10 1.01 0.41
Sulfur, ’3 Sominal Found 0.037 0.034 0.042 0 093
0.12 1.03 0.41
0.036 0.032 0.041
0.093
Tris(hydroxymethy1)aminomethane as Standard Alkali in Acidimetric Combustion Method for Determining Sulfur Albert C. Holler, Twin City Testing and Engineering Laboratory, 2440 Franklin Ave., St. Paul 14, Minn.
combustion method for determining sulfur T , 3)acidimetric suffers from the disadvantage that a 0.01iV sodium HE
hydroxide solution is used in t’he titration of the sulfuric acid. Standard 0.0LV sodium hydroxide is tedious t,o preparr. It has poor storage life, even though the st,orage bottle is equipped with a sodti-lime tube to keep out the carbon dioxide of the air. A literature survey indicated that tris(h?drox?.mcthyl)aminomethane (1) would be ideally suited For URP ti.‘ the stantlnrtl alkali in the acidimetric combustion mcthod for sillfur. It is a crystalline solid that can be prepx~rdi n high purity. Its hygroscopicity is comparable to that of mnmoii primarj- st:tnda d s . Keither the pure compound iior its soliltions h o r l ) carbon dioside from the air. The plI of its equivalence point is 1.7, which compares favorably wit11 thr cnrl point of pH 5.3 t:tkcln in the acidimetric combustion method. Stand:ird aolutiom of tris(hydroxymethy1)aminometh~n~~ are stable and eas!’ to prepare. They have been used in this lulrorntory for 2 y m r s and have given consistent results. Tris(hydroxymethyl)aminomethanc, knoa.n : t l ~ oas ’2-hytlt~osy2-amino-1,3-propanediol or trimetli~lol;riiiiiilometha~ie,(‘an l w obtained from Matheson, Coleman and Bell, ISast Rutherford, S . J. (Catalog S o . 7060). LITERATURE: C I T E D
(1) Fossum, J. H., llarkunas, P. C.. 23, 4 9 1 (1951).
Riddick, J A.,
.%N.~L. ( ‘ H L M .
(2) Holler, A. C., Klinkenberg, R , Ibid., 23, 1G9G (1951). (3) Holler, *4.C., Yeager, J. P., Foundru 72, 83 (1944).
Stirrer Assembly for Use under Pressure Vernell R. Shellman and Barney J. Magerlein, Research Laboratories, The Upjohn Co., Kalamozoo, Mi&.
w
studying certain chemical reactions under slight posltive pressure, up to about 20 pounds per square inch, difficulty Tas encountered in finding a satisfactory stirrer assembly. Several excellent assemblies designed for use m-ith HILE
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