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.
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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.
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