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
26,
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 t h a t 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.
Results Obtained with Apparatus 6BF
Standard Sample S o . 9d l5d 16e 20d
Carbon, % Xominal Found 0.20 0.21 0.10 0.12 1.01 1.03 0.41
0.41
Sulfur, ’3 Sominal Found 0.037 0.036 0.034 0.032 0.042 0.041 0 093 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
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
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 p r e p x ~ r di 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
1359
ANALYTICAL CHEMISTRY
1360 high pressure autoclave (qiiiprnent are available ( 1), but pressure stirrer seals for use xyith laboratory glassware apparatus are both scarce and unsatisfartory ( 3 ) . This note descrihee an adaptation of the semiball joint stirrer sea1 dewribecl by Patton ( 2 ) for use urider pressure. T h e seal assembly, shown in the diagram, consists of two pieces, the stirrer shaft and the housing. The ball portion of a 12/5 semiball joint is attached to the stirrer shaft,, while the socket portion of the semihall joint is fastened within the housing as shown. The shaft may conveniently be attached to the ball portion of the joint by slipping the shaft through the joint and sealing as shown in the diagram. The housing contains a gas inlet tube and R standard-taper joint to fit the desired reaction vessel.
When the apparatus is assembled for use, the pressure seal is made a t the union between the ball and socket portion of the semiball joint. A s the pressure on the system is increased, the joint is firmly pressed together, forming a leakproof seal. This union is lubricated with a few drops of silicone oil. Adequate pom-er for stirring is fiiiiiibhed by laboratory-t) pr stirrer motors.
Chein., in press) 1, is described here. 1Iodificatioris in certaiii dimensions will permit its use in othctr photoelectric colorimeters as well as for several other lengths of light path. The schematic drawing illustrates the fpatures of the cell.
Two flat plates of borosilicate glass ( 2 nun. in thickness) were cut to the desired dimensions and ground along their long edges to about a 45' angle. Rolled strips of copper wire (0.007 inch in thickness) were placed between the glass plates to act as spiicers. I n order to secure the position of the plates and spacers, each end of the assembly was wrapped with nickel wire. A strip of glass rod, drawn out to approximately 0.5-mm. diameter, was fused along the gap at each side. The copper wire spacers were then removed with nitric acid. A piece of capillary tiibing was attached to one end, and a standard-taper joint was sealed to the other. Space a t the ends \vas krpt a t a minimum, so that only a small sample of liquid (slightly less than 1 ml.) was needed to fill the cell.
p
4 I
SIDE VIEW
This seal vas P iwes.;f 1111- used under pressures up to 20 pounds per square inch : higher pressures were not investigated. I n several experiments a constant pressure of about 65 em. of mercury was maintained for 24 hours. 4CKNOW LEDGM ENT
The authors are indebted to Ti'. X. DeWolff for the glass blowing and to E. E. Beak for preparation of the drawing. LITERATURE CITED
(1) Komarewsky, V. l., Riess, C . H., "Catalytic, Iieactions," in A. Weissberger, ed., "Technique of Organic Chemistry," rol. 11, p. 1, Interscience. Sew York. 1948. (2) Patton, J. T.. J . Che7n. Ediic. 28, 207 (1951).
(3) Rushton, J. H., "hIixing," in -1.Weissberger, ed., "Technique of Organic Chemi~try,"vol. 111, p. 99, Intrrscicnce. Sew York, 1950.
Short-light-Path Absorption Cell for Routine Colorimetry Doyle C. Udy, Western Wheat Quality Laboratory, Field Crops Research Branch, Agricultural Research Service, U. S. Department of Agriculture, Pullman, Wash.
w-
HEN routine dilutions are required in colorimetric. analysis, faster and more accurate measurements can be made with a suitable short-light-path absorption cell. Such a cell, designed and constructed for use in an Evelyn photoelectric colorimeter [as used in the author's method of estimating protein (Cereal
1 2 2 MM.
ii
%5FJOINT
By securing a Ti25 standard-taper receptacle joint in the lo\\-ri. end of the tube holder (by means of a conveniently adapted rubbri~ stopper), the absorption cell may be placed in or taken out of' the tube holder easily. A length of capillary tubing was used to connect the receptacle joint to a stopcock and water trap. The trap was connected to a water aspirator, which provided :t partial vacuum for pulling the sample liquid through the ahsorption cell. Irrcgularitics in the cell spacing are of no consequence, :is t li(: (-ellcan easily he returned to the same position. This \vas f:icditated 1))- replacing one of the small screws in front of the tiihc holder hy a longer scrpxv to provide a fisrd position for the Iiorizontal rapillary arm of the cell. Formation of small air bubbles in the wll presented :t n i ; i , i c i i ~ prol)lem, until it \vas learned that flushing the cell with 1 or 2 nil. of n solrition rontaining a small amowit of n-capryl alcohol in acetone will prevent the formation of hubldes, A 0.5% solution is ample. Apparently a trace of alcohol is left on the glass siirfaces, siifficient to prevent the formntiou of any bubhlcs \ v l i ( ~ i i \wter is drnrc-n through the cell. In practice. only one flushing at the start of a series of meuswernents is required. Clcaning Iietveen samples is unnecessary, : ~ n dthe wll is kept full of liquid by closing the stopcock after :t few millilitrrs of :i new undiluted sample is run through the cc~ll. ACKXOW LEDGMENT
The author is indebted to Gporge E, Harris, glassbloncr :It the State College of Washington, for making the cell.
