Comparison of Tellurium and Selenium as Catalysts for Kjeldahl Digestion R. B. BRADSTREET The Bradstreet Laboratories, 1138 Spring St., Elizabeth, X . J .
LTHOUGH considerable work has been done on selenium
A and its compounds as catalysts for the Kjeldahl method,
Table I.
little has been published on the use of tellurium and its compounds. I t might be reasoned that because selenium and tellurium are analogs, the catalytic effect of tellurium would be much the same as that of selenium. Illarionov and Soloveva (Q), in discussing selenium and tellurium, state that the catalytic effect of the elements is similar and proportional to the amount used. In a survey of the effect of various amounts of selenium on the Kjeldahl digestion, Bradstreet (1) found that when samples of approximately the same size were used, very little difference in time of clearing of the digest was found with an increase of selenium. Furthermore, a definite loss of nitrogen occurred with amounts of selenium in excess of 0.25 gram. If this is true of selenium, the possibility exists that tellurium may act in the same manner. Gresin [ 3 ) states that tellurium is a good catalyst, and that the speed of decomposition of the sample depends on the amount of catalyst used. In the present investigation, using varying amounts of tellurium, little difference in digestion times was noted, but in comparison with selenium, digestion was appreciably slower. In the majority of the determinations, tellurium catalys s gave results m-hich were erratic, could not be correlated Kith an increase of catalyst, and were, in most cases, lower than the calculated percentages. Operating conditions were standardized as far as possible to minimize errors. Electric heaters were used for digestion and distillation. The reduction of the nitro compounds was accomplished by the use of salicylic acid. PROCEDURE
Samples were weighed into 300-ml. Kjeldahl flasks and 35 ml. of concentrated sulfuric acid containing 1 gram of salicylic acid were added. The flasks were allowed to stand for 30 minutes in the cold. Five rams of anhydrous sodium thiosulfate were added, and after t%e reaction had subsided the heaters were turned on low heat until the mixture blackened. The heat was then shut off and the flasks were cooled. Ten grams of potassium sulfate containing varying amounts of catalyst were added. Vigorous heat was applied until the digestion cleared, at which point the heat was reduced and the contents of the flasks were boiled gently for 1 hour. After the flasks had cooled, 125 ml. of distilled water were added. To the diluted and cooled digest, 165 ml. of 35% sodium hydroxide were carefully added, so that two distinct layers were formed. A small piece of low melting paraffin and several pieces of mossy zinc were added and the flasks were connected to the distillation rack. Davisson (2) distilling bulbs were used. The flasks were swirled gently to mix the two layers and heat was applied. Distillation was continued for 1 hour after boiling started, and the distillate was collected in 500-ml. Erlenmeyer
Table IT. N1 Calcd., ComDound rn-Dinitrobenzene p-Sitrobenzoic acid p-Nitroaniline 1-Aminobenzothiazole Acetanilide Anthranilic acid
%
16.68 8.39 20.30 18.67 10.36 10.21
Tellurium 15.94 8.46 20.01 14.06 10.23 10.12
Sodium tellurite 15.51
7.92 18.93 13.93 9.80 10.15
0.10
Tellurium Used, Gram 0.25 0.50 0.75 Per Cent Nitrogen Found Acetanilide (10.36%
Te T e 4- C u S 0 ~ 5 H 2 0 ~ T e f FeSO4.7HzOb
10.00 10.22 10.10
10.23 10.16 10.14
10.16 10.27 10.22
i.00' .. .
Nz)
10.14 10.28 10.30
10.33 10.30 10.22
Anthranilic Acid (10.21% Nz) Te Te Te
++ CuS04.5HzOa FeSOc7HzOb
9.86 9.94 9.82
Te Te CuSOc5HzO" T e f FeSO4,7HzOb
+
19.67 19.92 19.83
Te Te Te
+ + CuSOc5HzO" FeSO4.7HzOb
15.73 18.93 15.82
10.12 10.21 9.98
10.09 10.00 10.10
10.19 10.19 10.16
p-Nitroaniline (20.30% 20.01 19.97 19.29
19.65 19.31 19.61
10.22 10.18 10.23
Ns)
19.77 19.1 19.64
19.76 19.18 19.82
n-Dinitrobenzene (16.68% Sz) 16.94 15.85 15.94 16.06 16.20 15.95 15.90 15.40 15.88
15,713 15.65 16.00
0 2 6 gram cuSo4.5Hz0. b 0.25 gram FeSO,.
7Hz0.
flasks containing 50 ml. of distilled water, 25 ml. of 0.1 N hydrochloric acid, and 4 drops of a 0.1% solution of methyl red. At the end of the distillation, the flasks were disconnected, and the condensers and deliverv tubes were carefully washed out with distilled water. The distillate was titrated with carbonate-free 0.1 N sodium hydroxide. Blank determinations were run and suitable corrections applied. The relative merits of tellurium, tellurium and copper sulfate, and tellurium and ferrous sulfate were compared; the amount of tellurium varied between 0.1 and 1.0 gram. Four typical organic compounds, the nitrogen of which was easily reducible to ammonia, were used. The results, shown in Table I, seem to indicate the unsuitability of tellurium as catalyst in elemental form or in combination with copper sulfate or ferrous sulfate. The possibility of its use as a catalyst in the form of sodium salts led to further investigation and comparison with similar compounds of selenium. Ten different catalysts and catalyst combinations were used on six organic compounds containing nitrogen in various forms. Except in the cases of ferrous sulfate and copper sulfate in combination with selenium and tellurium, 0.25 gram of catalyst was used. The mixed catalysts contained 0.25 gram of each component. The time of clearing of the digestion mixture averaged 30 minutes, and all samples were given 1 hour afterboil. The results of this comparison are shown in Table 11. In
Per Cent Nitrogen
Sodium tellurate 15.80 8.12 19.21 18.80 9.79
10.17
Relative Merits of Tellurium Catalysts
Catalyst Copper Ferrous sulfate sulfate and and tellurium tellurium Selenium 16.06 15.90 16.66 8.14 8.08 8.38 19.97 19.29 19.96 18.56 18.53 10.1~ io:i4 10.34 10.21 9.98 10.25
-
1012
Sodium selenite 16.08 8.37 19.54 18.47 10.28 10.23
Sodium selenate 16.20 8.38 20.06 18.51 10.27 10.22
Copper sulfate and selenium 16.64 8.41 20.27 18.49 10.26 10.26
-
Ferrous sulfate and selenium 16.64 8.43 20.26 18.46 10.31 10.25
V O L U M E 21, NO. 8, A U G U S T 1 9 4 9 nearly all cases, tellurium alone, tellurium compounds, and combinations of tellurium with ferrous sulfate or copper sulfate gave low results. Of the selenium catalysts, selenium alone, or with ferrous sulfate or copper sulfate, was satisfactory. Sodium selerlite and gave slightly loR-er results in cases. It may be concluded that tellurium is not generally suitable as a catslvst for the Kjelt1,thl digestion.
1013 LITERATURE CITED
Bradstreet, R.B,, CHEY., 4 s k L , ED., 12, Gj7 (1940). (2) Davisson, B. S.,J . Ind. Eng. Chem., 11, 466 (1919). (3) Gresin, Yu. D., F a r m . Zhur., 1937, S o . 2 . 104-9 (4) Illaiionov, V. V., and Soloveva. N. A . , Z . anal. Chcm., 100 328-43 (1936).
R E G L I V E DJ u l y 12, 194%
Simplified Gas Microanalyzer C L i R E N C E N. STOVER, J R . , WILLIAM S. PARTRIDGE,
AND
WARRER M. GARRISON1
L'niversity of Vyorning, Larumie, Fyo.
LTHOUGII the Saunders-Taylor method ( 1 , 2 ) for the micro-
A analysis of gas is rapid and accurate. it has certain discidvantages. The custom-built multiway stopcock around which the apparatus is designed is relatively espensive and inconvenient to obtain. Likewise, the design of the combustion chamber requires an undue amount of care to prevent overheating the grease on the ground joint through which the chamber is connected to the apparatus. The desirable features of the method can be retained in a simplified form which is easily fnhricatrcl from standard stopcocks and ground joints.
0
to the tungsten electrodes. \Vith this design the filament could he operated as long as required without cooling the ground joint, which was lubricated with Bpiezon X. In a typical analysis the reaction tube was evacuated through D and volume F was evacuated through one side of stopcock G. The other arm of G was connected to a reservoir of gas to be analyzed. During the evacuation the mercury level in .V was kept below the mark a t H by applying vacuum through stopcock L a t J . When the pressure in F was 10-5 mm. or Iomer, a sample of gas was added through G . The mercury level was raised to I by cautiously opening L to the atmosphere. The difference in height of the mercury menisci a t I and in manometer 31 was a measure of the gas in volume 7'. Stopcock C was then rotated and the gas was forced into the appropriate reaction tube by raising the mercury level. After a period of time determined by experiment, the mercury was lowered to H and C mas closed. The gas was then compressed again to I and the manometer was read. The difference between the two manometer readings after correction for residual gas in the reaction tube was a measure of the volume change in the reaction tube used. The residual gas correction was calculated from the volume ratio of A and F ; for the apparatus shown this value was 0.00441 or 0.417&
A representative analysis of a four-component determinate misture is given in Table I. The gases in these samples were purified by the techniques outlined by Saunders and Taylor ( 2 ) . The modified analyzer is easier to build and more readily kept in operation than previous designs, I n general, the analytical difficulties encountered by Saunders and Taylor are still present.
h
Table I.
Analysis of a Standard Sample Taken,
Found, hlm.
H2
17.1
CO
32.4
17.3 17.1 32.8 32.0
Component
Figure 1. Diagram of 3Iicronnalyzer
The 1-inni. capillary two-n-ay stopcock, C, replaced the multiway stopcock in the original Saunders-Taylor design. The stopcock plug and reaction tubes, A , were evacuated througll D ,which was connected to high vacuuni. Gas to be analyzed was passed irito A by rotating the plug 180". Tubes holding reagents for various determinations had 10/30 ground joints and were interchangeable at B. These tubes were similar to those used by Saunders and Taylor. The reaction tube shown was used for combustions and was a modification of the origin:tl design. The two leads were 1-mm. tungsten and the filanierit was made from three turns of platinum wire spot-n-eldcd 1
Present addresb, University of California. Berkeley, Calif.
Mm.
CHI
68.2
GHs
14.7
68.5 68.1 14.0 11.8
IIowerer, the small empirical correction used h y them in cn1c.ulnting carbon dioside contractions can be neglected if not more than l C % escess osygen v a s added to the hydrocarbon fraction prior to combustion. This correction, the need for n-hich they attributed to stabilization of ozone on t,he walls of the n-atercooled combustion tube, apparently may be neglected, if, RS in the present design, the combustion tube is air-cooled and can, as a result, attain a higher wall temperature during combustion. LITERATURE CITED
(1) G a r r i s o n , W. hl., a n d Burton, hZ., J . Chem. Phys., 10, 730-9 11942)). ( 2 ) Saunders, K. W., 2nd Taylor, H. h.,Ihid.,9, 616-26 (1941). RECEIIE D July 23, 1048.
