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same samples by the present modification. Full titration data are shown for the first four samples.
Considerable experience with this modification of the Jones method has shown that in duplicate experiments the blank determinations should check within 0.5 cc. 0.1 N acid while Table 111-Determinations of Nitrate Nitrogen in Tobacco by Jones 0.2 cc. is usual. With tobacco samples containing 0.1 per Method a n d b y Modified Method cent or more of nitrate nitrogen duplicate determinations I TONES METHOD 1 MODIFIEDJONESMETHOD should agree within 5 per cent of themselves. With samples 0 1 N 0.1 N of lower nitrate content a slightly greater variation may be HC1 0.1 N NOa HCl 0.1N NOa O’’ SAMPLE with HCl nitrowith HCl nitro- 7;:-admitted. These conclusions are exemplified by the data of reduc- blank gen reduc- blank gen base Table I. tion tion To illustrate the wide variation in nitrate content of tobacco cc. cc. Per cent cc. cc. Per cent cc. grown with different fertilizers, the data in Table I V are 13.55 1.85a 0.31 21.4 given. 4.73 1.30 0,079 16.6 5.23 1.44 0.090 17.0 It is of particular interest to observe that the proportion 15.15 1.00 0.35 5.4 of nitrate nitrogen in the field crops is lowest in the tobacco 0.09 0.25 grown on sodium nitrate fertilizer. This, of course, is due to 0.20 0.13 the rapid leaching of this substance from the soil under field conditions. The nitrate in the hot-house crop on poa 0.6 cc. to be added to this figure for blank on reduced iron powder used. b Data obtained by Analytical Department of Connecticut Agricultural tassium nitrate fertilization, where no leaching could occur, Experiment Station. was unusually high. The hot-house crop grown without fertilizer contained no nitrate whatever, even the delicate Table IV-Nitrate-Nitrogen a n d Nicotine-Nitrogen Content of Tobacco Grown under Application of Different Nitrogenous Fertilizers qualitative tests being negative. Nitrate nitrogen may (Results calculated on air-dry basis) therefore vary from zero to over 1 per cent of the air-dry TOTAL NO2 NICOTINE NICO- weight of the tobacco leaf and is the most highly variable FERTILIZER NITROGEN NITROGEN NITROGEN TINE nitrogenous constituent of this plant that we have yet encountered. % % % % Although this method is chiefly designed for the investiFIELD CROPS-CURED TOBACCO None 2.54 0.113 0,321 1.86 gation of tobacco, there are many reasons why it may prove C&&eed meal 3.19 0.296 0.346 2.00 advantageous for the determination of nitrate in other plants, 2.63 0.093 Sodium nitrate 0.258 1.49 4.00 0.779 Ammonium sulfate 0,294 1.70 particularly where these contain high proportions of amide 3.71 0.598 0,335 1.98 Urea 2.79 0.213 Calcium nitrate 0.336 1.99 nitrogen.
1
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Castor pomace
2.45
HOT-HOUSE CROPS-FRESH
None Cottonseed meal and castor pomace Potassium nitrate
2.04 5.2 4.9
0.121
0,352
2.04
0.141
0.816 2.30 2.21
LEAF
0.000
1.19 0.722
Literature Cited 0,398 0.382
While the-agreement between the two methods is fairly close, it is clear that the variation is irregular and in several cases is 20 per cent or more of the quantities measured.
(1) Assocn. Official Agr. Chem., Methods, 1925, p. 66. (2) Bailey, Nolan, and Mathis, Connecticut Agr. Expt. Sta. Rept., 1927, p. 338. (3) Busch, Ber., 88,861 (1905). (4) Folin, J. Bid. Chem., 29,329 (1917). (5) Jones, IND.ENG.CHEM.,19, 269 (1927). (6) Seydell and Wicher, Z . angew. Chem., 24, 2046 (1912).
A New Volumeter Using Water as the Measuring Medium’ J. A. Fries 137 PARKAvE., STATECOLLEGE, PA.
HE chemist or research worker, especially in dealing with gases, frequently needs to know the exact volume of a particular set of apparatus, as well as the volume of reagents used and the displacement values of other filling materials, etc., so that he can at the end of an operation compute the residual contents and dispense with the final sweeping-out process. But, aside from the measuring by means of filling with some liquid, there is apparently no convenient method for such volume determinations. The method presented herein is simple and accurate, and uses water as the reagent or measuring medium. The volumeter is constructed of materials found in most laboratories, and simply by coupling in different sizes of additional water containers it can be made to suit almost any size of apparatus. Further, the method is applicable to any Condition of vapor pressure from nothing to that of complete saturation in the presence of liquid water.
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Received April 5, 1929.
Underlying Principle
Assume that a flask or any other apparatus containing air is connected air-tight to the upper end of a tube, such as a buret, which is filled with water to a definite height, the outlet end being open to the air. If, after the pressure of the gases in the apparatus has been made equal to that of the atmosphere, the tube is opened, the water in the tube will empty only to within a certain distance from the outlet end. The vertical distance of the column of water remaining in the buret represents a condition of equilibrium for the total volume of the particular apparatus plus connections, and the atmospheric pressure. Thus the change of water level in the buret, from zero down, is a measure of the total expansion of the air volume due to a definite change in pressure, and this change in pressure is indicated by the height of the water column from the water level to the outlet end of the tube. The barometric pressure minus the pressure of this water column equals the pressure
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ANALYTICAL EDITION
Vol. 1, No. 3
of the gas mixture in the apparatus. A similar condition of come, and consequently water becomes a handy means for equilibrium can be obtained by compression of the gases, accurate volume determinations. but the vapor complications were found to be more confusing I n a room where the temperature remains practically conand difficult to handle and hence only the method suited for stant there is little danger of error from diffusion of vapor expansion will be given. from the buret back into the apparatus. The several centiTheoretically the height of the column of water (reduced to meters of small-bore connections are a very efficient safemm. Hg) in the buret should be the correct measure of the guard, and by careful manipulation of the stopcocks in pressure change of the gas, but practically there is a slight filling the buret and in equalizing the pressure, the operation error due to surface tension and capillarity. I n order to can be repeated a large number of times without introducing overcome this interfer- a noticeable error by vapor diffusion. ence, in part a t least, The slight cooling effect which accompanies the expansion to allow the water to of the gases during a volume determination is considered reach its level with negligible, several minutes being allowed for equalization greater accuracy, and before the buret reading is taken. to be able to use the Use of Volumeter same water repeatedly, the end of the buret is Certain preliminary checking and measurements are necesallowed to dip under sary. The accuracy of the buret must be ascertained by water. weighing the water delivered, allowing a definite time of 3 Description of Voluto 5 minutes for drainage, and the volume factor computed. meter A table should be made converting the distances between The volumeter con- the cubic centimeter marks on the buret directly into centisists of a carefully cali- meters. After the connections on the volumeter have been tested brated 50-cc. buret, A , graduated in 0.05 cc. for tightness, the volume of the space above the 0-cc. mark and capable of being on the buret and the two stopcocks D and E is determined read to 0.01 or 0.02 by weighing or measuring the water required to fill. Likecc. accurately. T w o wise the total volume from 0 cc. to the end of tube G, where small-bore connecting it connects with the apparatus to be tested, is determined. glass tees, B, are pro- These volumes can also be checked by the volumeter itself. vided with three stop- Other factors required in the determination are the usual cocks C, D, E. The ones for volumetric work with gases. It is necessary to have wooden stand, H , has a the correct reading of the barometric pressure. A sensipiece cut out of the base tive correct thermometer is needed to get the temperature so that it can be used of the room air and the water used in the buret. It is also a t the edge of a desk or important to know the vapor pressure in the air of the roomother support when an in other words, in the apparatus to be tested. For this purextension tube to the pose a wet and dry bulb or a sling psychrometer can be used, buret is needed. At the the vapor pressure being computed according to the followlower end of the stand a smooth sheet-metal plate, L, is ing formula (I):* fastened. On this plate at the proper place a horizontal line, e = e’- 0.00074b (t - t ’ ) the 0-om. line, is drawn, and a t measured intervals from this where e = vapor pressure in mm. Hg, e’ = maximum vapor other horizontal lines indicate the distances in centimeters. pressure at the temperatue of the wet bulb, b = barometric The buret is wired securely to small wooden blocks on this pressure corrected for temperature, t = dry bulb, t’ = wet stand, the 50-cc. mark coming exactly over the 0-cm. mark bulb reading. on the metal plate. It has been assumed in connection with this work, that A 400-cc. lipped beaker, I, rests on a flat-bottom tray, and vapor, t constant temperature, under any degree of saturais adjusted so that the surface of the water as it stops over- tion so along as liquid water is not present, upon expansion flowing is exactly opposite one of the centimeter lines. A follows Boyle’s law. It has also been assumed that vapor in small glass tube attached to the end of the buret reaches almost to the bottom of the beaker. K is a rubber tube for a given space, over water and at constant temperature, is not influenced by changes in pressure, although its perdrawing the water into the buret from the beaker, and G centage relation to other gases varies according to pressure is a tube connecting with the apparatus to be tested. Glass changes. Reference to vapor pressure in millimeters of tubes should be used wherever possible, and where rubber mercury is a quantitative expression which enables one to tubing is necessary in the connections it should consist of employ the percentage relation of vapor to other gases in the short pieces of thick-walled tubing. A volumeter of this size is suitable for determining volumes computations. MANIPuLAmoN-The apparatus to be tested is connected up to at least 2 liters. to the volumeter a t G, stopcock C open, D closed, and E open. Beaker Z is filled with distilled water of the same Complications Due to Vapor and Cooling temperature as the surrounding air. The temperature of I n the system whose volume is to be tested a partial the water is carefully noted. Water is drawn up into the saturation of water vapor may exist, and in the buret and buret and adjusted to the zero mark. Stopcock E is closed, some connections is a small volume of fully saturated vapor D opened, and C closed. Enough distilled water is poured over water, and when air enters the buret vapor forms until into the beaker to assure an overflow when water is added its saturation pressure is reached. These complications might from the buret. Stopcock F is fully open, the time noted, at first appear to prevent the use of water as a medium for and allowed to drain a definite time, 3 to 5 minutes. F is volume determination. But the vapor difficulties can be over* Italic numbers in parenthesis refer to literature cited at end of article.
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closed and the water level read as accurately as possible, using a reading glass if necessary. Example Apparatus tested-a laboratory wash bottle Barometric pressure = 729.5 mm. a t 23’ C. = 726.57 mm. a t 0” c. Room temperature = 27.35” C. = 27.057 mm. saturated vapor tension Water temperature = 27.35’ C. Vapor pressure in room air = 9.73 mm. Volume of space above 0.0 cc. mark = 8.978 cc. Buret reading = 36.69 cc. Height of water column = 31.513 cm. Correction for capillarity = 0.33 cm. water The corrected volume read on the buret is the total expansion of gases from all sources, and the corrected volume of the column of water is the pressure change corresponding to the change in volume. This increase in volume includes the expansion of the gas mixture in the flask, expanding as a true gas since no water was present, the expansion of the 8.978 cc. of air above the water in the buret, and the vapor added in the buret to change the mixture from a state of partly to one of completely saturated vapor. Calculations
I n computing the results the best procedure is first to eliminate both the amount of vapor added in the buret and the total originally saturated volume above the buret water, and in the example given that plan is followed: 36.69 cc. x 1.0019 (buret factor) = 36.760 grams or cubic centimeters corrected
31.039 cc. X 0.73554 (factor for cc. HzO to mm. Hg) = 22.830 mm. He 72657 229830 = 703.74 mm. pressure in flask (22.830 + 726.57)lOO = 3.1422 per cent change in pressure (36.760 cc. X 676.683) + 703.74 mm. = 35.347 cc. dry air in total expansion (8.978 cc. X 699.513) f 726.57 mm. = 8.644 cc. dry air in original saturated volume (8.644 cc. X 726.57) c 703.74 mm. = 8.925 cc. dry air a t 703.74 mm. Hg pressure 8.925 8.644 = 0.281 cc. expansion 35.347 cc. (dry air in total expansion) 0.281 cc. = 35.066 cc. dry air from flask in volume increase At this point the vapor which was added and the 8.978 cc. originally over water have been completely eliminated from the problem. The original vapor pressure in the flask was 9.73 mm., which is equal to 1.339 per cent of the total pressure and hence the dry air = 98.661 per cent of the total. (35.066 c 98.661)lOO = 35.542 cc., which represents 3.1422 per cent of the total volume. (35.542 + 3.1422)lOO = 1131.12 cc. total, and subtracting from this the 35.54 cc. increase leaves 1095.68 cc. as the volume of the flask. The theoretical volume computed from the weight of water required to fill the flask was 1096.25 cc. Trials with two flasks coupled together gave on one day a value of 2143.78 cc., and on another day 2144.53 cc. The theoretical volume for the two flasks was 2144.65 cc. These results are considered satisfactory, and show the accuracy of the method when operated under fairly good conditions. Literature Cited ~~~
-
-
(1)
-
Chemiker Kalender, 1923, Pt. 11, p. 127.
Bimetallic Electrodes for Titrations Involving a Change of Hydrogen-Ion Concentration’ Raymond Matthew Fuoss SKINNER, SHERMAN & ESSELEN, INC., BOSTON, MASS.
The following electrode pairs have been used for POmotor stirrer, buret, and a HE necessity arose in tentiometric titrations involving a change of hydrogenpair of electrodes, which were this laboratory for a method of t i t r a t i n g ion concentration: antimony-lead, antimony-amalconnected to the potenticertain highly colored colgamated copper, bismuth-silver, a n d copper-copper ometer through a reversing oxide. All of these gave satisfactory results if d u e switch. The electrodes were loidal a l k a l i n e s o l u t i o n s . Bimetallic electrode systems precautions were taken; for general acidimetric a n d soldered to copper lead-wires, for oxidation-reduction titraalkalimetric work, however, the writer prefers the and were simply hung Over antimony- amalgamated copper Pair. the edge of the beaker so that tions have been described by The use of two suitably chosen metallic electrodes they were about half im. Willard and Fenwick (8)* and by firman ( 3 , 4 , 5 ) . Furman as discussed in t h i s paper suggests various industrial mersed. The soldered junc(4) a l s o s t a t e s t h a t t h e applications-for example, indicating, recording, a n d tion was coated with paraffin amalgamated gold electrode Process control equipment in cases where a change of to prevent contamination of may beused to followneutraliPH occurs.z T h e applicability of the m e t h o d for the electrode when the eleczations of hydrochloric acid volumetric determinations of metals has been sugtrode was rinsed with acid. or sulfuric acid, and Todd gested. Method (7) has patented the use of A definite volume of “unknown” was pipetted into the the cadmium-antimony alloy-iron pair for determination of hydrogen-ion concentrations. It was therefore decided to beaker and diluted to about 150 cc. The electrodes were investigate further the possibilities of such systems for the inserted and’ standard solution was added a t one-minute problem in question. The characteristics of four electrode intervals in successive portions of decreasing size until the pairs have been studied and are reported in this communica- magnitude of the change of voltage with portion of solution added gave warning that the end point was near. The tition. tration was then carried over the end point by adding at 60Apparatus second intervals equal portions (usually 3 drops) of standard The apparatus consisted of a Lee& and Northrup No. 7654 solution. The electromotive force usually became nearly pH indicator (one scale division equals 2 mv.), titration beaker, but not quite constant in 60 seconds; the value a t exact 60-second intervals was noted for the curve, however. The 1 Received November 3, 1928. reason for this procedure is twofold: First, the location of * Patent application has been made to cover such industrial uses. * Italic numbers in parenthesis refer to literature cited at end of article. the end point on the graph is made sharper, as a rule, by this
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