Apparatus for Trapping Ammonia in the Kjeldahl Method for Nitrogen THOMAS J. POTTS Ralston Purina company, St. Louis 9, M o .
T
HE apparatus described below has been used satisfactorily in this laboratory for 20 years, to seal the receiver used in catch-
dipping the delivery tube into the standard acid. It offers several advantages: It does not require a delivery tube that must be removed from the solution before turning off the heat; a smaller quantity of solution may be used in the receiving flask; the action of the trap is automatic; its dependability has been proved by the laboratory's record in various collaborative check samples; and it can be easily made by anyone experienced in working glass. The block-tin delivery tube from the condenser and the tube from the trap extend through a No. 10 rubber stopper into a 500ml. wide-necked Erlenmeyer flask used as the receiver. I n operation about 2.5 cm. (1 inch) of water are put into the trap; more water is undesirable because of the danger of siphoning it out of the trap before completion of the distillation. The apparatus will trap any ammonia vapors that are driven through the condenser by retaining them in solution. When the distillation is complete and the heat is turned off, the lower pressure inside the system will cause the solution in the trap to siphon into the receiving flask. The concentration of ammonia in the trap is very low. Experience has shown that it is not necessary to rinse the trap with water a t the end of the distillation. Using the trap and C.P. ammonium sulfate as a standard, recoveries have been found quantitative with amounts of nitrogen as high as 140 mg. per determination. The acid used is standardized according to the procedure of the Association of Official Agricultural Chemists ( I ) .
ing the ammonia distillate in the determination of nitrogen.
10
LITERATURE CITED
Used in analytical laboratories where nitrogen or protein is determined as a regular routine, the trap automatically catches the ammonia in the distillation step, eliminating the necessity of
(1) ASSOC.Official Agr. Chern., Official and Tentative Methods of Analysis, 5th ed., p. 650, Par. 7 (1940).
Aqueous Solutions of Alcohols as Confining Liquids for
Gas Analysis
t
KENNETH A. KOBE1 AND GEORGE E. MASON University OF Washington, Seattle, Wash. vacuum-distilled. Dissolved gases were removed from the water and the compounds (except glycerol and dihYdroxY diethyl ether) by refluxing for 20 minutes or by vacuum distillation. The absorption bulb and gas buret qrere maintained a t 250 & 0.10 c. The carbon dioxide (99.87, purity) was saturated with water vapor from the solution by passage through a SPiral-tyPe bubbler maintained a t 25' C. Values of the vapor pressure of the water in the solution were taken from the literature or calculated from
HE use of solutions of alcohols, particularly glycerol, as T c o n f i n i n g liquids for gas analysis has been mentioned in numerous papers since it was first reported by Burgess and Wheeler ( I ) . Using a solution of equal parts of glycerol and water previously saturated with coal gas, they reported that "the gases do not dissolve in such a mixture to any appreciable extent, and its use is more convenient than that of mercury". The advantage of the low freezing point of such a solution, has been mentioned. The authors have investigated the solubility of carbon dioxide in aqueous solutions of alcohols which might be satisfactory as confining liquids and compared these solubility data with those obtained for solutions of inorganic salts previously recommended. Carbon dioxide was selected because it is the most soluble gas commonly encountered in gas analysis. A survey of the literature ( 4 ) showed that carbon dioxide was sufficiently soluble in aqueous solutions of monohydric alcohols to preclude them from further consideration.
Table
I.
Solubility
OF Carbon Dioxide in Aqueous Alcohol
Solutions (Temperature 25" C., partial pressure of COz 760 mm.) Solution Gas Solubility of Compound Used Concentration Used Absorbed Con arb MI. M1. , Ml.a Wt. % 20.57 0.823 0.754 Xone 0.0 24.99 0.592 0.542 40.0 80.00 29.62 Glycerol Glycerol .50.0 50.00 25.55 0.512 0.468 Glycerol 50.0 50.00 23.10 0.462 0.423 Sulfuric acid 5.0 Ethylene glycol 60.0 49.99 31.36 0,627 0.574 50.00 32.68 0.654 0.599 Ethylene glycol 40.0 Ethylen: glycol 20.0 50.00 36.31 0.726 0.666 Dioxane 60.0 50.00 76.13 1.523 1.395 8-8'-Dihvdroxv 60.0 24.99 15.80 0.633 0.579 - ethyl. ' etherc 75.0 50.00 55.66 1.113 1 . 0 2 0 Tetrahydrofurfuryl alcoholc \I1 of COz a t 25' C and 760 mm. dissolved er ml of solution. b Ml: of COz calculated to.0" C. and 760 mm. f i s s o h e d per ml. of solution. C This solution reacted with mercury.
EXPERIMENTAL
The apparatus and tcchnique are those employed previously ( 2 , 3). The organic compounds were of reagent quality or were 1 Present address, Department of Chemical Engineering, University of Texas, Austin, Texas.
78
ANALYTICAL EDITION
January, 1946
79
c.,
Raoult's law. The total pressure maintained in the apparatus dioxide plus the vapor pressure Of the was 760 mm. Of solution a t 25" C. The solubilitv data are given as milliliters of carbon dioxide a t 760 mm. and25" C. dissGlved in 1 ml. of solution. From this is calculated the Bunsen coefficient, a, which is the milliliters of carbon dioxide, calculated to 760 mm. and 0 O C., dissolved in 1 ml. of solution ( 4 ) Although the precision of the results is 0.002, it can be consideEed that the accuracy of a is 0.005. The data are given in Table I.
acidified sodium sulfate solution below 16O this solution i l l continue to dissolve less gas than the acidified glycerol solution. Only a t temperatures below the cryohydric point would the acidified glycerol solution have advantages. The cryohydric temperature of saturated aqueous sodium sulfate solution is and of sodium chloride is -21. 0 aqueous solution of sodium chloride is recommended for use at temperatures to -20°C. ( - 4 ' F . ) .
c.
0
LITERATURE CITED
DISCUSSION
(1) Burgess and Wieeler, J . Chem. SOC.,97, 1923 (1910). (2) Kobe and Kenton, IND.Ero. CHEM.,ark^. ED.,10, 76-7 (1938). (3) Kobe and Williams, Ibid., 7, 37-8 (1935). (4) Markham and Kobe, Chem Reviews, 28, 519-88 (1941). THIRD paper in series; for NOS. 1 and 2 688 (a, s).
The Bunsen coefficient for an acidified 50% glycerol (0.423) is almost twice that found for the 20% sodium sulfate plus 5% sulfuric acid solution (0.247) previously recommended ( 2 , 3 ) . Although sodium sulfate decahydrate will crystallize from the
Electronic Timer JOHN KEENAN TAYLOR
AND
JOSEPH GILMAN REID, JR.
National Bureau of Standards, Washington,
R
E C E S T n-ork in the physical chemistry laboratory of this bureau involved the use of a solenoid-operated, enclosed glass pump. The electronic timing device described by Bechtold (1) appeared particularly well suited for controlling this solenoid because of its simplicity, ease of construction, and readily controlhblr, pulse rate. However, this timer proved unsatisfactory in operation since, under the conditions which obtained, the gas-filled triode (885) had an average service life of only about 12 hours. S o current-limiting element was included in the triode plate circuit. Thus, the charging surge supplied to capacitor C2 (Bechtold's designation) was, upon breakdown of the triode, in excess of the rated peak current for the tube. This overload caused the tube t o fail prematurely. Insertion of re-
r
1
D. C.
sistance to limit the peak current to the specified maximum (300 milliamperes) resulted in feeble actuation of the relay. Satisfactory operation required the use of a more sensitive relay, or of a tube having a higher peak current rating. I n the improved circuit given in Figure 1 the type 885 tube has been replaced by a type 2050 gas-filled tetrode and a currentlimiting resistor has been inserted. This resistor, &, has a value of about 170 ohms and limits the charging surge of C2 to less than the rated maximum (1 ampere) of the 2060 tube: Resistor R j has been added to limit grid current and rheostat R, to reduce arcing of the relay contacts on an inductive load, such as a direct current solenoid. The modified circuit has proved highly satisfactory as evidenced by over 200 hours of operation, including continuous periods of as long as 60 hours, with no evidence of tube failure. Its readily adjustable pulse rate, obtained by manipulaPI tion of potentiometer R1 and the adjustability of the range of rates depending upon the values of RI, RP,and CI, make it applicable to a wide variety of timing operations.
" ,
CI
ACKNOWLEDGMENT
0 1 6d
D t IN
TOLOAD
ll0V
Suggestions made by P. J. Franklin in connection with the design of this circuit are gratefully acknowledged.
AC
Figure 1.
Circuit for Electrcn:c Timer
CI, 3 paper condensers, 400 wv, P r f d . each; Cn,250 wv. electrolytic condenser, 8 r i d Ca paper condenser 450 wv 1 aM.1 Ri I-megohm potentiometer N o 6 taper1 Ra 50 000 D 1-watt carbon; R s R; lO,OOOD, 1 -wati carbon;'Rs 1 -megbhm 1 -watt carbon; Re 150 n'5-watt wire-koind; R;, 100 D, 9-amperc'rhoostat; T,6.3-volt 3-ampere dlament tran;former; R e , double-pole, double-throw relay, PO00 n coil; F, P.O-ampere furor S doublo-pole, single-throw toggle switch; 9050, RCA type PO50 gas-filled tetrode; PI, P, relay contact point;
LITERATURE CITED
(1) Bechtold, I. C., IND.ENG.
C H ~ MAXAL. ., ED.,14, 429 (1942).
