MAY 15, 1935
ANALYTICAL EDITION
191
TABLE 111. COLOR IN TRINITRO COMPOUNDS Compound 1 3 5-Trinitrobenzene 2’4’6-Trinitrotoluene 2’4’6..Trinitroanisole 2’4’6..Trintroben.oic acid 2’4’6-Trinitrobensatldeh de 2:4:6..Trinitrophenylhy%asine
Reagent Red Red Red Red Brownish red Brownish red
Diluted Linht red Faint Dink Faint ‘pink Pink Fajnt brownish red Faint brownish red
HC1 Added Blood red Red Orange red Red Brownjsh red Brownish red
CHaCOOH Added Wine red Red ~ . . No change Red Brownish red Brownish red
2 4,6. Trinitrophenol 2’4 6-Trinitrophenylacetate 2’4’6..Trinitro-n-cresyl acetate 2:4:6..Trinitro-?n-~resol
Reddish orange Reddish orange Orange yellow Orange
Orange No change No change Lemon yellow
Reddish orange ReddiEih brown Slightly darker Lemon yellow
2,4,6. Trinitroresorcinol
Greenish yellow
Orange yellow
No change
Greenish yellow
No change
2,4,6. Trinitroresorcinyl acetate
Greenish yellow
No change
No change
No change
No change
2 4 6-Trinitromesitylene
None
Light orange red Greenish yellow Yellowish green Light lemon yellow Light greenish yellow Light greenish yellow None
Acid Solution Made Basic with NaOH On HC1 aoln. On CHsCOOH s o h Reddish brown Blood red Rad Red Oiange yellow Red Pink Pink Brownish red Brownish red Dark browniah Dark brownish red red. Yellowish orange Reddish orange No change Reddish brown No change Color. lightened Reddish orange Reddish orange
None
None
None
None
None
None
None
None
None
None
2:4:6.Trinitro-1,3-dimethyl-5ter-butyl benzene
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4,6 trinitro-l,3-dimethyl-S-ter-butylbenzene, no color is produced. The steric effect of the nitro group in the isomeric dinitrobenzenes is noteworthy. m-Dinitrobenzene readily responds to tlhe test, p-dinitrobenzene gives a reddish yellow which soon passes into a greenish yellow color, while o-dinitrobenzene gives no color at all. The test is extremely delicate in most cases-for example, 2,4-clinitrobenzene is sensitive to one part in 1,500,000. Since mononitro compounds fail to respond to the test, it is possible to detect traces of di- or trinitro compounds in mononitro compounds as impurities by this method, but it is not possible to detect dinitro compounds in the presence of trinitro compounds.
cussed above. These colors are true only for the benzene series. If it is desired to produce a less intense color, a smaller amount of alkali should be used in the test. In Tables I, 11, and I11 are given the results with various nitro compounds under different conditions.
Procedure
Literature Cited
One-tenth gram of nitro compound is dissolved in 10 ml. of acetone and 3 ml. of 5 per cent sodium hydroxide are At this point a purplish added with amear for dinitro comDounds, while a blood red color k p & l c e d by trinitro dodies. Mononitro compounds fag to give a color. Exceptions to these tests have been dis-
Summary Mononitro compounds of the benzene series produce no color with the reagent, dinitro compounds a purplish blue color, and trinitro compounds a blood red color, The presence of the amino, substituted amino, or hydroxyl group in the nucleus interferes with the test. Acylation of these groups does not remove the interference. The test is extremely sensitive. (1) Bitto, B. von, Ann., 269, 377 (1892).
$ ~ ~ ~ ~ ~ ~ ~ (Iss6), ~ ~ ~ ~ ~ (4) Reitzenstein and Stamm, J . prakt. Chem., 81, 168 (1910).
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(5) RudolDh, 2. anal. Chem., 66, 239 (1921). (6) Taylo; and Rinkenbaoh, U. S. Bur. Mines, Bull. 219,122 (1923). R~~~~~~~January 30,1935
.An Improved Slow-combustion Pipet for Gas Analysis D. J. PORTER and D. S. CRYDER, School of Chemistry and Physics, Pennsylvania State College, State College, Pa.
S
INCE 1876 when Coquillon (3) proposed the use of a platinum spiral for slow-combustion analysis of hydrocarbon gases, this method has come to be practically standard. In the usual method the combustion pipet is filled with oxygen or air and the combustible gas is slowly introduced a t the top of the pipet where it comes in contact with the heated platinum spiral and combustion ensues (9,4). Improvements upon the basic design of this pipet have been made by Weaver and Ledig (8) and Matuszak (7). A deposit of carbon is often found on the pipet wall above the spiral after a series of combustions, and when burning some gases such as isobutane, combustion is incomplete to the extent that when the gases are passed the second time over the hot spiral an explosion often occurs. I n one pipet designed to secure more perfect combustion and decrease the danger from explosions, the gas to be burned is introduced through a capillary platinum jet located in the
side wall of the pipet and impinges directly upon the heated spiral (I). Convection in this case should aid in keeping the spiral surrounded by oxygen rather than hot products of combustion, yet it is possible that the combustible gas might be swept away before reaching the heated zone. To secure safety in operation and accuracy in results, complete combustion must be secured, and the most logical method of securing complete combustion is to burn a preheated mixture of the combustible gas and an excess of oxygen. Any such mixture with a sufficiently high concentration of combustible to be useful in gas analysis is explosive, so the usual pipet cannot be used. Drehschmidt (6) passed combustible mixtures through 100 mm. of platinum capillary tubing of 0.7 mm. internal and 2.5 mm. external diameter, which he heated by a Bunsen flame. His platinum tube deteriorated rapidly with use and had to be renewed because of leakage. Weaver and Ledig
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INDUSTRIAL AND ENGINEERING CHEMISTRY
192
(8)describe forms of glass or quartz capillary tubes containing
fine heated spirals which are useful for determining small amounts of oxygen in a gas, or small traces of combustible in oxygen or air. Lutz (6) has found such apparatus not satisfactory for use in general slow-combustion analysis.
Design In a preliminary design of a slow-combustion pipet in which the combustible gas could be mixed with oxygen and passed over an ignitor, the gas was led through 2.5 cm. of platinum tubing of 0.9 mm. internal and 1.0 mm. external diameter with an insert of 0.45-mm. platinum wire: The small annular space remaining for passage of gas prevented passage of flame or explosion wave for all combustible mixtures tried, including electrolytic gas at very low flow rates. One to two millimeters from the
VOL. 7, NO. 3
A sample of gas requiring from 40 to 60 cc. of oxygen for combustion is measured and stored in the potassium hydroxide pipet. After a thorough rinsing of the manifold and manometer with nitrogen, 100 cc. of oxygen are measured in the buret. With stopcock H open, oxygen is run into the pipet until the mercury level is 1 to 2 cm. below the rim of the cup. By closing H and raising the mercury level in the pipet, any mercury remaining in I or B is blown up into the enlarged section, J, above the stopcock. The mercury level is brought to just below the rim of C and the spiral heated to a bright red. With the combustion pipet shut off from the manifold, the remaining oxygen is thoroughly mixed with the combustible sample by passing back and forth from the potassium hydroxide pipet to the buret several times. With the pressures in the pipet and buret equalized and H always closed, the gas is allowed to flow slowly into the pipet. By decreasing the current through the spiral as the gas rate is increased, the sample may be burned as fast as 40 cc. per minute. After all the gas has been passed into the pipet, 10 cc. are withdrawn and passed in again several times to burn the unexposed portions in the connection between buret and capillary tip, and then the entire volume is passed over the spiral a few times before determining the resulting volume and carbon dioxide. Any combustible gas in the potassium hydroxide or connections will yield an additional fraction of a cubic centimeter of contraction and carbon dioxide on a repeated series of passes over the spiral.
Performance Typical combustion data on commercial hydrocarbon gases of unknown purity or composition were secured by the same operator to compare the performance of this new pipet with that of the standard Burrell pipet. Each column of Table I represents the average of three combustions. On the basis of the values of n for saturated hydrocarbons (CnHin+J,the percentage of ethane in the mixture is calculated to be 59.9 and 56.8 per cent by the new and Burrell pipets, respectively, compared with the measured value of 58.3 per cent.
7T‘
TABLEI. TYPICAL COMBUSTION DATA
U
SIDE WEW- 3.x ARM Nor SOWN
FIGURE1. DIAGRAM OF PIPET end of this inlet tube were placed the various ignitors. An unsupported platinum spiral, platinum spirals on quartz and refractory supports, and a re ractory mixture containing thorium and aluminum oxides, alundum cement, and water-glass binder with internal s iral of platinum wire were tried as ignitors. It was found $at, because of the radiating power of the refractories and the protection which they afforded the platinum wire, the gas could be burned more rapidly on them than on the bare platinum. However, this design was not satisfactory, as the tip of the platinum tube became hot enough to cause carbon deposition, even in the presence of 100 per cent excess oxygen. In a short time the tube became fouled, and the analyses were inaccurate. Unless the gas was passed into the pipet a t a slow rate the platinum tube became overheated at a point dangerously near the inlet end. Consequently, some method of cooling the capillary was thought necessary, and the pipet illustrated was developed. The pipet is constructed of Pyrex glass as shown in Figure 1. A platinum tube, A , 2.5 cm. long, 0.9 em. internal diameter, is sealed into capillary B and projects 2 mm. above the level rim of cup C. A length of 0.45-mm. platinum wire, D, is inserted into the top of the platinum tube t o the bend in B. A ten-turn helix E, of 0.2-mm. platinum wire is supported 3 mm. above the tip o! the tube by 0.45-mm. platinum leads which are brought into two side arms, F , to which steel terminals, G, are secured with sealing wax.
Operation When the pipet is filled with mercury, the side arms and cup should be clean and dry. With stopcock H open, the mercury level is raised above the tip of the platinum tube. Stopcock H is then closed and mercury run into B until it rises in I above the level of H. By lowering the mercury level in I any air trapped in B is forced out by the rising mercury, and then with H open the remaining space in the pipet may be filled with mercury.
Methane Burrell New 23.66 22.70
Sample taken! cc. Hydrocarbon in sample, cc. 23.33 22.38 Carbon atoma, caldated 1 . 2 1 6 1.189 Hydrocarbon found, per cent 98.65 98.60
Ethane Burrell New 16.98 18.82 17.36
19.32
1.914
1.866
102.29 102.66
Methane 41.74% Ethane, ’68.26% Burrell New 19.76 20.38 19.31 2 0 . 1 0 1 . 6 1 2 1.694 97.77
98.62
It appears that the accuracy of results obtainable with this pipet is equal to the accuracy obtainable with the Burrell pipet. For the greatest accuracy, the platinum spiral should be located not less than 3 mm. above the tip of the platinum tube and the temperature of the platinum tube should be kept as low as possible. This pipet offers the added advantage of complete safety in operation, as evidenced by the fact that over 125 combustions have been performed b y both experienced and inexperienced analysts on a pipet of this type, using gases varying from methane-hydrogen mixtures to isobutane and n-pentane, with no flash-backs or explosions.
Literature Cited (1) Bayley, C. H., Can. J . Ibeseurch, 7, 680 (1932). (2) Burrell, G . A,, Seibert, F. M., and Jones, G. W., Bur. Minea, Bull. 197, 51, 83 (1926). (3) Coquillon, J., C m p t . rend., 83,394 (1876); 84, 458, 1503 (1877). (4) Dennis, L. M., “ G a s Analysis,” p. 145-7, New York, Macmillan Co., 1929. (5) Drehschmidt, H., Ber., 21,3242 (1888). (6) L u t z , W. A,, Master’s Thesis, Pennsylvania State College, 1934. (7) Matuszak, M. P., IND.ENG.CHEM., Anal. Ed., 6, 77 (1934). (8) Weaver, E. R., and Ledig, P. G . , J. IND. ENO.CHEM.,12, 368 (1920).
RECEIVED January 21, 1935.
