V O L U M E 22, NO. 12, D E C E M B E R 1 9 5 0 separation is sufficient t o rrmove iron, chromium, and other elements Tvhich hydrolyze in an alkaline medium. Very large quantities of tungsten require two separations. Large amounts of nickel or large amounts of cobalt with medium quantities of nickel usually require reprrcipit,ation of the potassium cobaltinitrite (Table I). If retreatment of the precipitate is indicated, return the paper to the original beaker and add 15 ml. of nitric acid and 15 ml. of
sulfuric acid. After the vigorous action ceases, evaporate slowly to fumes of sulfuric acid. Raise the cover of the beaker with a glass hook, increase the heat, and evaporate the solution to dryness or until fumes of sulfuric acid cease to escape. If the amount of cobalt is large, it may be impossible t o obtain complete dryness owing to the formation of potassium bisulfate. If preferred, the potassium cobaltinitrite precipitate may be dissolved i n hot dilute hydrochloric- acid and the solution evaporated to dryness. To the dry salts add 3 to 5 grams of tartaric acid and 7 5 ml. of water and warm until solution is complete. Seutralize with potassium hydroxide solution, adjust t,he acidity with acetic acid, and repeat the precipitation of the potassium cobaltinitrite :is described above. However, less water and potassium nitrite solution may be used if the amount of cobalt is small. Filter after a t least 4 hours of standing and wash with cold 3% solution of potassium nitrite. Hold the filtrate if a determination o f nickel is required. FINAL DETERRIINATION O F COBALT
1521
water, stir, add about 150 ml. of hot water to dissolve the cobalt sulfate, and cool to about 20” C. Render the solution ammoniacal adding an excess of about 60 to 70 ml., add about 2 grams of sodium bisulfite, and electrolyze for 6 to 8 hours on a platinum gauze electrode using a current density of 0.2 t o 0.3 ampere per sq. dm. Dissolve the weighed deposit in concentrated nitric acid. Evaporate to dryness several times with hydrochloric acid and determine the sulfur as barium sulfate. Deduct the sulfur found from the weight of cobalt. For most routine work it is sufficient to deduct 0.5 mg. from the weight of the cobalt deposit. INTERFERING ELEMENTS
So far, no combination of elements has been found which directly interferes with the method proposed here. In the simultaneous presence of large quantities of iron and arsenic the latter should be expelled. The interference of barium, calcium, strontium, and lead was investigated. Soluble salts of these elements, while not preventing complete precipitation of the cobalt, definitely interfere with the separat,ion from nickel. If a mineral or ore is decomposed with nitric and sulfuric acids, the sulfates of thpse elements remain insoluble and can be filtered off. The amount of calciuni sulfate soluble in dilute sulfuric acid does not interfere with the precipitation of the cobalt nor with the separation of cobalt from nickel. lIagnesium sulfate does not interfere.
In most instances the electrolytic determination of the cohalt If electrolytic equipment is not available, the c o -
CORROBORATION AND VERIFICATION
is preferred.
l)alt may be determined-after the nitrite preripitate is fumed with nitric and sulfuric arids-colorimetrically on aliquot portions n-ith nitroso R salt, or ammonium sulfocyanate, gravimetricsnlly as Co301follom-ing precipitation with l-nitroso-2-naphtho1, or volumetrically by titration with pot,assium ferricyanide. ELECTROLYTIC DETERMINATIOS
Return the paper containing the potassium cobaltinitrite to the original beaker, add 20 ml. of nitric acid and 20 ml. of sulfuric acid and, after the vigorous action ceases, heat until fumes of sulfur trioxide escape. If necessary, add more nitric acid to destroy organic matter. Dissolve the sulfates in a small amount of water and again evaporate to fumes of sulfur trioxide. Repeat this fuming to expel all nitric arid. Cool, add 50 nil. of cold
Cobalt was d e t e r m i n d in various metals, alloys, ores, and aitificial mixtures and the results are presented in Table 11. LITERATURE CITED
(1) Baubigny. Ann. chi???.p h y s . , 17, 103 (1890). (2) Brunck, 2.angetc. Chem., 20, 1847 (1907). (3) Classen, “.lusgewaehlte Methoden,” Vol. I, p. 431, Braunschweiy. Vieweg and Sons, 1902. (4) Fischer, P o g g . A n n . , 71, 545 (1847). ( 5 ) Hillebrand and Lundell, “hpplied Inorganic .lnalysis,” p. 331. S e w York, John JJ-iley 8: Sons, 1929. (6) Scott, “Standard Methods of Chemical Analysis.” Vol. I. p . 312, New York, D. Van Kostrsnd Co., 1939. RECEIVED
l f a r c h 9, 19jo.
Apparatus for Determining Freezing Points at Saturation Pressure - -
From Time-Temperature Freezing and Melting Experiments AUGUSTUS K. GLASGOW, J R . , KED C. KROUSKOP’, AND FKEUEKICK D. KOSSINIL Xational Bureau of Standards, Washington, D . C . The apparatus previously developed for determining freezing points in air at atmospheric pressure from time-temperature freezing and melting experiments has been remodeled to permit determination of freezing points at saturation pressure (in vacuum). Details of the modifications of the apparatus and procedure are described. Illustratiye experiments on several hydrocarbons and organic sulfur compounds are given.
T
HIS report describes the modifications which have been made in the apparatus and procedures previously described ( 1 , 2 ) for determining freezing points in air at 1 atmosphere from timetemperature freezing and melting experiments to permit determination of freezing points at saturation pressure (the condition Present address, Carnegie Institute of Technology, Pittsburgh Pa.
in which the substance is under its own vapor pressure-that is, without air or other gases present). The report also gives illustrative experiments on several compounds. This modified apparatus may be used to determine the freezing points of substances which must be handled out of contact with the atmosphere. I t may also be used t o determine the difference
1522
ANALYTICAL CHEMISTRY
Figure 1 (Right).Assembly of Apparatus A. B.
Motor Brass wheel
C. Steel connecting rod, pinned a t center D. Brass bearing
E . Brass coupling F . Friction clutch G. Brass coupling (see Figure 2)
H.
Stainless steel rod (see,Figure 2)
I. Sylphon bellows (see Figure 2) J.
Brass sleeve K. Brass coupling L. Brass tube M ,M ' . Brass bearing N . Brass tube 0. Copper tube with standard taper P. Two parts of stirrer shaft threaded together here Q. Stainless steel rod R. Standard-taper ground-glass joint, 40/80, borosilicate glass S. Glass hooks, borosilicate glass T. Ground-glass spherical socket, 18/7, borosilicate glass connection t o vacuum system U. Stainless steel coupling V . German silver tubing W . Aluminum cage stirrer 9. Space between outer glass wall of thermometer and well filled with amorphous high melting wax to about 1 inch above coil of platinum resistance thermometer Y. Ground-alass suherical joint. 18/7. borosilicate glass Z. Standard-taper ground-glass joint, 12/30, borosilicate glass a. Kickel tubing, '/irinch outside diameter, '/winch wall thickness h b' I , Rubber tubing C. Brass tee d . Copper tubing, l/e-inch outside diameter C. Platinum resistance thermometer f. Dewar flask, borosilicate glass v. Three-way ground-glass stopcock, borosilicate zlass t o drying tower 6. Co&ection Connection t o vacuum
Figure 2 (Far Right). Details of Stirring Assembly
!I G H
A.
Steel rod, l/r-inch diameter B . Brass coupling, lower portion recessed for Sylphon bellows soft-soldered a t this point C. Sleeve, brass tubing '/a-inch outside diameter, '/ai-inch wall thickness D , Sylphon bellows, brass, one-ply, 0.75-inch outside diameter, 0.5-inch inside diameter, 7.6 inches long, 17 corrugations per inch, maximum stroke of 1.7 inches for 7.5 inch length bellows capable of maximum pressure of 16; pounds per square inch (similar t o Fulton Sylphon bellows No. 1015) E . Aluminum support, block 1 by 1.625 inches a t base, bolted t o 0.25-inch brass plate on one end, c u t and drilled t o 0.875 inch-diameter t o clamp on brass sleeve on other end F . Brass coupling, s/a a n d 2/16 inch in inside and outside diameters, respectively: hard-soldered t o tube H , recessed on upper end and softsoldered t o Sylphon bellows. tapped a n d threaded t o hold sleeve C in bosition G. Aluminum sup ort, block 1 b y '/a inch a t base, bolted t o LJ-inch brass plate on one end. cut and drilled t o %/a-inch diameter t o clam; on brass tube on other end H . Brass tube, a/s-inch outside diameter, hardsoldered t o brass bearing, I I, I'. Brass bearings with three '/a-inch holes drilled in recess, one as bearing for stirrer shaft, L , and two open to bellows for pressure equalization J . Aluminum support, block 1 b y l'/a inches a t base, bolted t o i/r-inch brass plate on one e n d ; c u t and drilled t o '/s-inch diameter t o clamp on brass tube on other end K. Brass tube, '/a-inch outside diameter, l/az-inch wall thickness, soldered to I and I' L Stainless steel rod, l/a-inch diameter, threaded on upper end t o fit coupling B , tapped and threaded on lower end t o fit lower shaft R .If. Copper tubing, a/a-inch outside diameter, flared on one end to form standard taper, iZ/so 217. Right angle braces '/r-inch brass angle, bolted t o '/r-inch brass' plate, supporting Transite collar P 0. Asbestos padding P. Transite block, cut and drilled for '/a-inch diameter with half of hole in each piece bolted to brass angle, two parts of block bolted t o each other, three 3/~s-inchdiameter holes drilled in block to accommodate sDrinz clamps. Q Q. Spring clamps, three spaced around block t o connect t o glass hooks (C in Figure 3) R. Stainless steel rod, '/s-incli diameter turned t o '/winch diameter and threaded on upper end S. Stainless steel coupling T. Stirrer C. Thermometer weli (see Figure 3) V . Seeding well (see Figure 3) W'. Standard-taper ground-glass joint, 40/50, borosilicate glass Platinum resistance thermometer ~~~~~
~
I
x.
_
W
x
S
T
V O L U M E 22, NO. 12, D E C E M B E R 1 9 5 0 in the freezing point of :t sample a t saturation pressure and of the same sample in air at atniospheric pressure. For many coinpounds, having a normal heat of fusion and a low solubility for air a t the freezing point, the difference in the two freezing points will
1523
he small, of the order of 0.005' to 0.05" C., but for compounds having a small heat of fusion and a normal or large solubility for air a t the freezing point, the difference in the two temperatures may be much larger. With the present apparatus and procedure, large differences could be determined readily, but additional precautions would be required for dctcrniining very small differrnrrs accurately. APPAH.Cr1JS .$ND PROCEDURE
The changes made in the ctpparatus previously described ( 1 , 2 ) \vert?as follows:
50 -
.4Sylphon bellows \vas f i t k d to thc metal stirrer and conricctcd t o the glass freezing tube in order to isolitte the atmosphere from the sample under observation. fixed re-entrant glass tuhc, in which the thermometer was inserted, ivits immersed in the sample (the re-entrant tube could have been eliminated, if desired, by using a large ground-glass joint on the upper part of the stem of the thermometer). A small glass tube, to the lower end of which was attached a curved Kovar bladc snugly fitted to the re-entrant tube for the thermometrr, was used to induce crystallization. Alterations were made in the freezing tube to permit introduction and withdrawal of the sarnplc without contact with the atmosphere. The assembly of the apy)nrutus is shown in Figure 1. 14.225
I
I
I 1
I
:
I
- 108 966' C
\
1
'\
0.Ol"C
1.3-BUTADIENE
I 10
I
I 20
I
I 30
I
TIME IN MINUTES
Figure 4.
.A 0
---F---
Figure 3. Details of Freezing Tube 9. Standard-taper ground-glass joint, 12/30, borosilicate glass B. Standard-taper ground-glass joint, 40/50, borosilicate glass C . Glass hooks, three, borosilicat,e glass D. Spherical joint, 18/7. borosilicate glass E. Internal walls of jacket of freezing tube, silvered F . Graded seal from Kovar metal t o uranium glass t o borosilicate glass G . Kovar tubing, 3 mm. in outside diameter H . K o r a r tubing silrer soldered here t o Kovar piece in form of curved blade, t o hold high vaciium I . Platinum wire t o hold Kovar blade taiit against glans well J. Kovar blade of same curvature as thermometer well
Freezing Experiment with 1,3-Butadiene at Saturation Pressure
.4 friction clutch was placed on the stirring mechanism. By trial, it was found desirable t,o adjust the clutch to yield at a lo:d corresponding to about 1500 grams, which was below the point, at which the forces of stirring endanger the glass apparatus. Figure 2 s h o w the details of the stirring assembly, except t,hr stirrer itself which is attached :it T , and the motor arid reciprocttting shaft a-hich are attached at d. This entire assemlily is attached rigidly to a thick brass plate, so that no strain is placed on the ground-glass joints, Ti' and M ,and so that proper alignment of the stirrer and the freezing tube is maintained. The assembly is arranged so that the metallic bellows may be replaced readily. The details of tho glass freezing tube are shown in Figure 3 . The g r a d d seal which joint the Kovar blade to the glass tube ( F , Figurr 3 ) can withstand very large and suddcn ch;tnges of temperature without breaking. The details of introduring, degassing, and tran.qferring samples under their own vapor pressure without contact with extraneous gases have licxen described ( 1 , s ) . A closed-end mercury manometer, sbout 1 meter long, is attached to the system for the purpose of observing the pressure in the system during the operations. For freezing points below room temperature, this manometer serves to give an a p roximate value ( t O . 5 nim. of mercury) of the vapor pressure of t i e sample
ANALYTICAL CHEMISTRY
1524
i001 "C
_ _ _ _ _ _ _ _ _ ---\?$ _---I I I
2-: :1 7 h Y L - I, 3 - BUT A D I ENE
]
ide was dropped into the crystallizing tube. For compounds with freezing points below about -50" C., a small amount of liquid nitrogen (contained in the Dewar flask a t f in Figure 1) was introduced into the crystallizing tube (through d and a, with suction applied through tube b ' ) , A tube containing material for absorbing water vapor and carbon dioxide is attached to the system a t h in order to keep water and carbon dioxide from entering and plugging the small tube, a.
All other parts of the apparatus and procedure were the same as previously described (1, 2 , 4 ) .
(ISOPRENEI
/
I
I
I
t
2
15.063
I
3.062
1.i;: 1 1
I3
I
j
/t:
I
I
I
I
I
I
I
I
I
-147.326'C
I
I
ETHANETHIO, (ETHYL hlERCADTAN)
I
I
I 23
I5
T Iv'E
Figure 6.
I
I
I
JI
25
h MINUTES
Freezing Experinient with Ethanethiol at Saturation Pressure
a t its freezing point during the time-temperature freezing and melting experiments. The stirrers used were similar t o the aluminum cage stirrer ( 8 ) and the Nichrome wire double helical stirrer (1 ) previously described, except that the dimensions were altered to fit the present freezing tube. Crystallization was induced in the sample under investigation in the freezing tube by cooling it to a temperature slightly below its freezing point and subjecting the sample to a "cold shock," as f 0 110 W S : For compounds with freezing points in the range from room temperature t o about -50" C., a small piece of solid carbon diox-
EXPERIMENTAL DATA AND DISCUSSION
Figures 4, 5 , and 6 show representative time-
mercaptan), respectively, a t saturation pressure Detailed information regarding the method of presenting these data and the significance of the letters on the time-temperature curves is given in previous papers ( b , 4 ) . I n order to determine the effect on the observations of the temperature of the additional layer of glass interposed between the thermometer and the sample by the re-entrant tube, measurements of the freezing point of a given sample of purified 1,3-hutadiene were made with the sample in air a t atmospheric pressure, both with and without the re-entrant tube, using the same thermometric system. Following are the relative values of freezing points obtained from five consecutive Experiments on the same sample of 1,3-butadiene, the liquid being cooled a t the rate of about' 0.7" C. per minute near the freezing point, taking the mean of the five experiments as a reference point: with no re-entrant tube, -0.0012", -0.0002", -0.0003"; with reentrant tube, +0.0010", +0.0008" C. The differerwes are within the experimental error of such observations. LITERATURE CITED
(1) Glasgow, d.R., Jr.. Krouskop,
K.C., Beadle, J . , Axilrod, G . D.. and Rossini, F. D., ANAL.CHEY., 20,410 (1948). (2) Glasgow. A . R., Jr., Streiff, -1. J., and Rossini, F. D., J . Researcii S a t ! . Bur. Standards. 35,355 (1945); RP 1676. (3) hIair, B. J., Termini, D. J., Killingham. C. B . , and Rossini. F.D., Ibid., 37,229 (1946); RP 1744. (4) Taylor, W.J., and Rossini, F. D., I h i d . , 32,197 (1944); RP 1585. RECEIVED J u n e 26. 1950. Investigation sponsored by U. 6 . Office of Rubber Reserve and performed a t the National Bureau of Standards in collaboration with American Petroleum Institute Research Project 6 o n analysis, purification. and properties of hydrocarbons.
Carbon Monoxide and Carbon Dioxide Gaseous Mixtures C. H. TOENSING' AND D. S. AMCKINNEY Carnegie Institute of Technology, Pittsburgh, P a .
I
T BECAME apparent, after a literature review, that available
methods were inadequate for the accurate analysis of gaseous niistures containing high percentages of carbon monoxide and the balance carbon dioxide and/or nitrogen. T h e quantitative determination of carbon dioxide in a gaseous mixture is relatively accurate and may be readily accomplished rvith a fair degree of precision by volumetric absorption, by gravimetric absorption, or by numerous special procedures. However, the precise determination of carbon monoxide is not so easily accomplished. The customary methods used to determine rarbon monoxide are usually involved, time-consuming, inac-
' Present address,
Brush Development Company, Cleveland, Ohio.
curate, and designed mainly for small amounts of carbon monoxide. A gas sample may be diluted to allow one of the available analytical methods to be used, but the additional manipulations and volume determinations introduce further errors. APPARATUS
Previous investigators (5) have stated that a gravimetric method of analysis is to be recommended for the precise determination of carbon dioxide. Because carbon monoxide is readily oxidized quantitatively to carbon dioxide, a very satisfactor? simple gravimetric analytical procedure for the determination of carbon monoxide and carbon dioxide n as developed.
