Conversion of “Percentage Concentration” of E. M. BURDICK
AND
Mash
or Beer to Gallonage
JULIAN CORMAN
Agricultural Motor Fuels Division Northern Regional Research Laboratory, Peoria, 111.
I
S C O R R E L h T I S G laboratory and plant fermentation data involving concentrations of mash or fermented beer a t this laboratory, it is frequently necessary to convert so-called “percentage concentration” to gallonage. This requirement arises because different systems are commonly used to express concentrations in the laboratory and in the plant. . I n the laboratory it is customary to express concentration on the basis of weight per volume, using metric units, while in the plant it is expressed as volume per weight, using English units. “Percentage concentration” is the weight, in grams, of original grains contained in 100 ml. of final slurry. “Gallonage” is t,lie volume,in U. S. gallons, of final slurry which contains one V. S. distillers’ bushel of original grains. Fhpressed mathematically,
the relationship between percellrage concentration and gallonage becomes: 56 X 453.59 X 100 = percentage concentration Gallonage X 3783 3 where 56 = pounds per U. S. diqtillers’ hu\hel of grain, 453 59 = grams per pound, and 3785 3 = nil. per U. S. gallon. From the above equation it can be seen that percentage concentration X gallonage = 671.04. Therefore, to change percentage concentration to gallonage or vice versa, it is only necessary to divide the constant (671.04) by whichever expression 1s given-for example, a 21 1% maqh or beer is equivalent to 671.04/21.1 = 31.8-gallon beer, or conversely a 31.Rgallon heer I $ equivalent to 671.04/31.8 = 21.1 % concentration.
Sensitive Test for Silver and the Halides PHILIP
S. BAKER AND J. H. REEDY
University of Illinois, Urbana,
SENSITIVENESS
W
HEX a solution of potassium iodide that has beensaturated with mercuric iodide is added to asilver chloride precipitate, a bright orange color is obtained. This reaction is very sensitive, anti has been m’ade tne basis for the following test for silver.
Since the test involves the separation of the silver as silver chloride ds a primary st,ep, the solubility of silver chloride is the limitiiig factor in the sensitiveness of the test. The effect of the concei1,tration of the iodide in the reagent is secondary in comparison. However, a high concentration of iodide is desirable, since it intensifies the color effect-that is, several drops of 0.1 M potassium iodomcrcurate may be required to give the same I I potassium iodomercurate. depth of color as a single drop of . I n general, the procedure will give a positive test for silver with a single drop of 0.001 J I silver nitrate using microtechnique. The sensitiveness thercfore approximates 5 micrograms of silver. Since the amount of silver chloride precipitate is the important factor, the sensitiveness of the test can be increased by concentrating the solution previous to the precipitation with hydrochloric acid.
PROCEDURE
.4 solution of potassium tetraiodomercurate is prc~purcd by shaking 24 grams of mercurir iodide with 100 ml. of warm molar potassium iodide solution. Upon standing, a small residue of mercuric iodide will remain undissolved and will settle to the bottom, leaving a saturated solution of the iodomercurate reagent. This solution is stable except for slight atmospheric oxidation, and in contact with mercuric iodide will undergo no noticeable change upon standing several months. The silver chloride is prepared as a suspension by adding a slight excess of dilute hydrochloric acid to silver nitrate. rlfter coagulation by warming and shaking, the precipitate is transferred to a small Kirsch funnel and washed thoroughly to remove any excess of chloride ions. The precipitate is aspirated to prartical dryness, and, after disconnecting from the vacuum, a drop of the iodomercurate solution is added, giving the orangered color. -4fe\v moments are allowed for the maximum color to develop. Thc color may be further intensified by drying the paper on a steam bath or in a drying oven. Prolonged hrnting must be avoidcd, since mercuric iodide is volatilg a t high temperatures. This procedure has been extended to include the detection of chloride and bromide by precipitating them with silver nitrate olution, and washing the precipitate until it is free from excess ,ilver ions. Silver in the form of silver iodide or silver sulfide cannot be detected in this way, since these salts are too insoluble t o react with the iodomercurate reagent. The test must be made without diluting the reagent, since dilution causes the separation of a red precipitate of mercuric iodide. This is due to the hydrolysis of the iodomercurate ion: Hg14-dilution Hg12 (red) 21-. One drop of water with 5 ml. of the reagent will produce a distinct red precipitate after standing 2 minutes, and a drop of the reagent with 10 ml. of water will ive a red precipitate in about the same time. I n order to avoif this interference, the silver halide is dried on the paper by aspiration.
+
Ill.
INTERFERENCES
Several ions interfere with this test for silver by forming yellow or red precipitates-.g., lead, mercurous, mercuric, bismuth, cupric, cadmium, stannic ions, and oxidizing agents in general. I n addition, alkaline solutions sometimes contain anions that form precipitates upon acidification--e.g., tungstate, thiosulfate, silicate, etc. With the exception of tungstic oxide, these precipitates give no colors with the reagent, but they may interfere by diluting the test. A411these interferences may be removed as follows:
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The solution is acidified with dilute nitric acid and warmed. Any precipitate of tungstic oxide, sulfur, silica, etc., is removed by filtration. The filtrate is then treated with dilute hydrochloric acid. If mercurous or lead ions may be present, chlorine solution or dilute nitric acid is added, and the mixture is t a r m e d . The precipitate is separated on a small paper in a Hirsch funnel and is washed with hot water as long as the washings show the presence of mercuric or lead ions. After the precipitate has been aspirated to dryness, a drop or two of the iodomercurate reagent is added. An orange precipitate indicates the presence of silver chloride.
Instead of the filtration technique, spot test or cone methods may be used. The necessary precaution against dilution of the reagent must be observed in both cases. Practically the same sensitiveness was found in all the methods used.
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