An Aspiration Method in Determining Ammonia and Other Volatile Gases L. -4.SARVER, UniJersity of AIinnesota, Illinneapolis, 3linn.
SPIRATIOK methods have been described for the microdetermination of ammonia and other volatile gaaes, but they appear not to have been adopted xidely by the profession as a whole. This is the more surprising in view of the considerable advantages of aspiration over straight distillation, and the well-known disagreeable tendency of the latter to give trouble by bumping. A step in the right direction has been made by Green ( 1 ) who has proposed distillation and agitation by steam. I n this method the steam has a triple function: it heats, it prevents bumping by stirring, and it sweeps out the escaping gases. TVhile steam is available a t some points in most laboratories, yet there are times and places where it is not conrenient to use it. For instance, the author wished to include the determination of nitrogen as part of the regular laboratory Ivork in large classes, and it was out of the question to set u p a sufficient number of stills, since steam was not piped to the desks in the analytical laboratory. Honever, suction was available, and i t was found possible to determine nitrogen very quickly, simply, and accurately by aspiration. The sample may be contained in either a Kjeldahl or an Erlenmeyer flask, fitted with a thistle tube which reaches the bottom and a n outlet tube leading to a petticoat bubbler in an absorption bottle, preferably of tall narrow form; an outlet tube from the latter leads directly to the suction line. It was determined by experiment that no entrainment of the reagents occurred from either of the flasks, even with vigorous
aspiration; at the same time the absorption of the ammonia, or other gas, is complete when an efficient bubbler is used. The gas may be liberated by addition of the reagent through the thistle tube while aspiration is in progress, with no danger of loss. Some heat must be applied, since quantitative removal of the gas is very slow a t room temperature; it may be supplied by direct heating or by a water bath. The process is complete in from 10 to 30 minutes, depwding upon the volume and the rapidity of heating. I n the case of ammonia, the gas may be absorbed in a small excess of standard acid, and titrated n i t h standard base, using methyl red as indicator. The aspiration method has a further advantage over straight distillation in that little dilution of the absorbent occurs. S o water-cooled condenser is necessary, although one may be used if desired. Only a small excess of the liberating agent need be used and, since there is no bumping, practically no attention is required. The time necessary for the complete removal of ammonia depends upon the rapidity of heating. Small volumes and rapid heating are of advantage where speed is important; on the other hand, a water or steam bath is to be preferred where i t is desired to run a series of analyses with a minimum of attention.
Literature Cited (1) Green, J., ISD. ESG.CHEM.,Anal. Ed., 3, 160 (1931). RECEIVED April 27, 1938.
Direct Determination of Iron in Malt Beverages PHILIP P. GRAY
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IRWIN RI. STONE, Wallerstein Laboratories, 180 >ladison Aye., New Yorh, N. Y.
T I S KSOWS that relatively small amounts of iron impair the colloidal stability of beer and cause development of abnormal tastes and off colors. The extent to which traces of iron, as well as other metallic elements, may function ab oxidation catalysts has been under consideration in the authors’ laboratories for some time and is receiving special study. There is obviously a need for a rapid and, a t the same time, adequately accurate procedure for carrying out iron determinations on beer, both as an aid in research worli in these directions and as a means of regularly scheduled control. Sormally, traces of iron are present in practically all beers. Iron which may occur in water and brewing materials, if not filtered out with the spent grains in the mash tub, appears to be very largely eliminated n-ith the coagulum which forms during kettle operations. Severtheless, traces remain and may be augmented by subsequent contact with iron surfaces. The amounts of iron found are usually 0.5 part per million or less. Yet amounts even slightly in excess of this concentration have been known to result in the development of a bitter taste, gradual acquisition of a dark color, lossof brilliance, and chill-haze development. It is also believed that, as aresiilt of its catalytic influence on oxidation, the shelf life of packaged beer is definitely shortened. Usual procedures for determining iron in beer, based on
classical methods, call for a rather lengthy, involved treatment, to reduce the sample to a form suitable for analysis. Methods generally applicable may be found in reference books (4, 6 , 7 ) . Siebenberg and Hubbard ( 6 ) adapted the ferrocyanide method for use in beers. This method calls for evaporating and ashing, dissolving the ash in hydrochloric acid, precipitating copper, lead, and tin with hydrogen sulfide, removing hydrogen sulfide, oxidizing the iron, a phosphate separation to separate the iron from any nickel, and finally dissolving the iron-containing precipitate and determining the iron colorimetrically nit’h ferrocyanide solution. Aside from the length of time involved, i t is evident t’liat opportunity for loss or contamination, representing unknown sources of error, may be presented by the number of manipulations involved in such a procedure. I n the method as developed bj. the authors, it has been fo>;,nd possible to determine the iron in beer quickly and directly without having to ash the beer or to subject it to any other preliminary treatment. In contrast with the cocsiderable time required for existing methods, results are obtainable within 45 minutes. The reagent utilized in this procedure is 2,2’-bipyridine (ala’-dipyridyl), Hill ( 2 ) investigated and (described its use for the determination of iron and reported on its applicability
