T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
3 50
1'01.
12,
No. 4
VANADIUM
SUMMARY
( I ) HISTORICAL-Rodejal showed t h a t acid solutions of the alkali metavanadates give a red precipitate somewhat soluble i n water. O.OOOOOI g. of vanadium per cc. gives a reddish coloration changing t o green. The author claims t h a t this is a more sensitive qualitat i v e reaction than t h e potassium sulfocyanate or hydrogen peroxide reactions. Rodeja2 in another paper claims t h a t cupferron does n o t quantitatively precipitate vanadic salts in dilute acid solutions but does precipitate vanadyl salts. Turner3 in an attempt t o separate vanadium from tiraniurn found t h a t a metavanadate was completely precipitated by cupferron in I per cent solutions of hydrochloric or sulfuric acids. The precipitate was washed with one per cent sulfuric acid containing 1.5 g. cupferron per liter and then ignited t o V205. His Pesults are shown in Table XXIV.
The present status of cupferron as a quantitative precipitant is as follows: 1-Cupferron has been successfully used for t h e quantitative determination of copper, iron, titanium, zirconium, thorium, and vanadium. 2-Many elements interfere with the determinations. I n any given determination t h e partial or complete precipitation of copper, iron, titanium, zirconium, thorium, and vanadium must be considered in addition t o the following known interfering elements: lead, silver, mercury, tin, bismuth, cerium, thorium, tungsten, uranium in the quadrivalent condition, silica, vanadium, and in certain cases when present in excessive amounts, phosphorus, alkali salts, and alkaline earths. ,?-The cupferron method should not be employed unless the qualitative composition of t h e material t o be analyzed is known, or a most careful quantitative examination of the ignited and weighed cupferron precipitate is made. 4-Cupferron can be used advantageously in certain separations, such as iron from manganese, and iron and titanium from aluminum and manganese.
TABLE XXIV VzOs Taken VzOs Found
EXPT. NO.
....................
1 2 .................... 3 .................... 4 ....................
G. 0.1655 0.1655 0.1655 0.1655
G. 0.1655 0.1657 0.1652 0.1658
Error G. +O. 0003
+o .0002 -0.0003 +0.0003
Table XXV gives data obtained by Turner which led him t o conclude t h a t Rodeja's statement concerning the incomplete precipitability of vanadic salts b y cupferron was incorrect. EXPT. No.
I 2 8
TABLE XXV VzOa Taken
VzOs Found G. 0.0873 0.0882 0.2300 0.1954
G.
15 0.08731 16 0.0882' 17s 0.23002 18 0.1952z VzOs not reduced before precipitation. V d s reduced before precipitation, Filtrate from this experiment showed vanadium.
(2) FAVORABLE
CONDITIONS
FOR
PRECIPITATION-
F r o m t h e foregoing work i t appears t h a t quantitative determinations of vanadium by, cupferron can be obtained in one per cent hydrochloric or sulfuric acid solutions of the element in either the quinquivalent or quadrivalent condition provided the precipitate is washed with one per cent acid containing cupferron. (3)
SEPARATIONS
WHICH
HAVE
BEEN
Anales soc espafi. 5s. q u i m , 12 (1914), 305; Chem. Abs., 9 (1915),
2201
Anales
SOC.
e s p a d . $ 5 . quim., 12 (1914), 379; Chem. Abs., 9 (1915),
2202. 8 4
BUREAU OF
METHYLORANGEINDICATOR N HCl.. 8 . 2 8 cc. 0.1410 g . NH3 N HC1.. . . . . . . . . . . . . .8 . 2 7 cc. 0.1408 g. NH3 N HC1.. . . . . . . . . . . . . . 8 . 2 5 cc. 0.1405 g . N H I
.............
Av., 0.1407 g. NHs
CONGORED INDICATOR
N HC1.. . . . . . . . . . . . . . 8 . 2 7 cc. N H C I . . . . . . . . . . . . . . . . 8 . 2 1 cc. N H C I . . . . . . . . . . . . . . . 8 . 2 2 cc.
A m . J Sci., 4 1 (1916), 339; 42 (1916), 109. cit
0.1408 g. NHs 0.1398 g. NHs 0.1400 g. NH3
-
Av., 0.1402 g. NHI
The ammonia present was equal t o 0.1400 g. The fixing solution in this case consisted of 5 g. boric acid dissolved in I O O cc. distilled water. Adler3 in 1 9 1 6 published a modification of the method adapted t o t h e use of laboratories of t h e brewing industry, b u t as it has been impossible t o obtain a copy of t h e original we have had to take our information regarding his work from abstract^.^ N o data regarding his results are given b u t only an outline of his recommendations for the modification of Winkler's method. He used 50 cc. of a 4 per cent solution of pure crystallized boric acid in the receiving flask. The condenser tube 1 2
LOC.
DEPARTMENT OF AGRICULTURE, WASHINGTON, D. C. Received October 20, I919
P L A N T INDUSTRY,
I n 1 9 1 3 Winkler2 proposed'the substitution of boric acid for sulfuric acid in the fixation of ammonia distilled over in the course of the Kjeldahl method for t h e determination of total nitrogen. He tried both methyl orange and congo red as indicators, t h e results with t h e latter being slightly better than t h e former as the following figures show:
ATTEMPTED.
( a ) Vanadium from Ph~sphorzts-Rodeja~ claimed t h a t a satisfactory separation can be accomplished by acidulating with sulfuric acid, boiling with sulfur dioxide t o reduce the vanadium, expelling t h e sulfur dioxide with carbon dioxide, precipitating with cupferron, washing w'ith very dilute sulfuric acid, and igniting t o vanadium pentoxide. (4) I N T E R F E R I N G SUBSTANCES-since Very dilute acidity only is permissible many elements will interfere i n this determination. See THORIUM 4. ( 5 ) SUMMARY-It is certain t h a t t h e use of cupferron for the quantitative determination of vanadium will find application only in very rare cases. 1
BORIC ACID MODIFICATION OF THE KJELDAHL METHOD FOR CROP AND SOIL ANALYSIS' By F. M. Scales and A. P. Harrison
8
4
Published by permission of the Secretary of Agriculture. Z. angew. Chem., 26 (1913), 231. Z. ges. Brauw., 29 (1916), 161, 169. J . Inst. Brewing, 22 (1916), 50; Chem. Abs., 11 (1917), 3371.
Apr., 1 9 2 0
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
was allowed t o remain below the surface of the absorbing solution for the first 1 5 min. but after t h a t i t was raised so t h a t the subsequent distillate served t o rinse the end of t h e tube. The distillate should reach the absorption flask a t room temperature. Adler found t h a t 2 0 min. of vigorous boiling sufficed to distil all the ammonia. I n order t o obtain maximum accuracy in titration i t was necessary t o employ a color standa r d ; this was prepared by treating 2 5 0 cc. distilled water with 0.1j cc. of 0.1 N sulfuric acid and a few drops of methyl orange. The orange-yellow tint remained unchanged for a long time. The distillate, treated with the same amount of methyl orange, was titrated with 0.1 N sulfuric acid t o the same t i n t , and the ammonia content calculated from the volume of acid required, no correction being necessary for the boric acid present. The maximum amount of ammonia which was absorbed without loss by the quahtity of boric acid mentioned above (50 cc. of 4 per cent solution) was not determined, but i t exceeded 7 0 mg. The results were as accurate as when sulfuric acid was used for absorbing the ammonia. I n laboratories where it is necessary t o run a great number of nitrogen determinations, this modification is of special value because it requires only one standard solution, and since the absolute amount of boric acid in the receiving flask need not be accurately measured, a n unskilled assistant may do this part of the work; this rough measurement of the acid saves from one-fourth t o one-third of the time necessary t o obtain equally accurate results by the old methods. Where the acid solution is made so t h a t I cc. equals I mg. of nitrogen or some whole number multiple of this figure, the worker can read his results directly from the burette or else obtain them by the simplest mental arithmetic. For these reasons we have experimented with the method as a possible substitute for the one commonly used for the determination of total nitrogen in crops and soils. SOLUTIONS
The standard sulfuric acid solution was made up so t h a t I cc. equaled I mg. of nitrogen. The boric acid solution was made by weighing out 4 g. of the acid for each I O O cc. of distilled water used in preparing the Io-liter quantities. The boric acid was dissolved in water a t room temperature. Three indicators were employed: methyl orange, congo red, and bromophenol blue. With the first two it was necessary t o make up solutions containing the regular quantity of indicator in I j o cc. of water and sufficient acid t o produce the color t o be used for a match in the regular titration. The methyl orange was prepared in the usual way by dissolving one gram in 1000 cc. water; congo red, I part in I O O parts of 30 per cent alcohol. One-tenth gram of the bromophenol blue was heated with 3 cc. of 0.05 N sodium hydroxide till dissolved and then diluted t o 2 5 0 cc. with distilled water. The end-point of the bromophenol blue was observed by arranging an electric bulb within about 5 in. of a white surface near the burette stand in such a way t h a t the flask during the titration was between the bulb and the reflecting surface; under these conditions the
3.51
end-point was the disappearance of the purple color. The change is sharp and distinct. APPARATUS
The apparatus employed for these tests was an unmodified Kjeldahl digestion shelf and distilling stand with condensing tank. EXPERIMENTS
SULFATE-The method was first tested by distilling known quantities of nitrogen as ammonia into both sulfuric acid and boric acid. For this purpose a solution of ammonium sulfate containing approximately 0.5 mg. of nitrogen per cc. was used. Fifty cc. of this solution were pipetted into each of t h e Kjeldahl flasks and 2 0 0 cc. of distilled water and 5 0 cc. of saturated sodium hydroxide solution added. The resulting solution was boiled for 3 0 min. so that about 150 cc. of distillate passed over, and then 5 min. longer t o allow for clearing the delivery tubes. Two sets of 8 flasks each were titrated with congo red as an indicator, 3 drops being used in each determination; in one set j o CC. sulfuric acid solution and in the other 5 0 cc. boric acid solution were used i n the receiving flask. The excess sulfuric acid was titrated with ammonium hydroxide, I cc. of which equaled 1.011 cc. sulfuric acid. I n order t o make the results with the two absorbing solutions comparable, we added 3 drops of congo red t o zoo cc. of distilled water and then added 0.30 cc. of acid t o produce the same color as was obtained with I j o cc. distilled water, 50 cc. 4 per cent boric acid and 0.35 cc. of standard acid. I n the former case, a s the end-point comes while the solution is still acid, t h e correction of 0.30 cc. was added t o the burette reading for ammonia t o reduce i t t o what would be obtained if the end-point were taken a t the neutral point with this indicator. To correct for the presence of t h e boric acid i t was necessary t o subtract 0.3 j from t h e burette reading for sulfuric acid. Two additional sets of distillates in boric acid were titrated, one with bromophenol blue, 3 drops, and the other with methyl orange, 3 drops; in each case the correction constant was 0.3 cc., which was subtracted from the figures obtained for each determination as shown. AMMONIUM
TABLE I-NITROGEN RECOVERED FROM (NHa)zS04 SOLUTION SULFURIC ACID FIXING AGENT -BORIC ACID FIXING AGENT---. Congo Red Congo Red Bromophenol Blue Methyl Orange Mg. Mg. Mg. Mg. 26.20 26.20 26.15 26.25 26.15 26.10 26.25 26.10
Av.,
26.15 26.25 26,25 26.25 26.15 26.05 26.15 26.25
26.20 26.25 26.25 26.20 26.10 26.25 26.25 26.10
26.10 26.25 26.25 26.25 26.10 26.20 26.15 26.20
__
-
__
__
26.18
26.19
26.20
26.19
P R O C E D U R E WITH CROPS A N D sons-The crops were weighed, placed in a Kjeldahl flask, and 30 cc. concentrated sulfuric acid containing I O per cent phosphoric anhydride and 0 . 5 g. of anhydrous copper sulfate added before starting the digestion. The digested material in the acid was diluted with I 75 cc. of distilled water and treated with I O O cc. concentrated sodium hydroxide and a few pieces of mossy zinc. The distillates from these solutions were received in approxi-
352
T\HE J O U R N A L OF.I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTR'Y
Vol.
12,
No, 4
mately j o cc. portions of 4 per cent boric acid and tiSUMMARY trated with standard sulfuric acid, using bromophenol Winkler's modification of the Kjeldahl method in blue as a n indicator. This indicator was selected in which he proposed the use of boric instead of sulfuric preference t o any of the others because when used acid in the receiving flask is found t o be as accurate as under the conditions described for observing the end- when the latter reagent is employed. Ninety-five mg. of point, the disappearance of the purple color (which nitrogen as ammonia can be recovered in the discould also be observed through a screen as in hydrogen- tillate when j o cc. of 4 per cent boric acid is used. ion determinations) is sharper and more distinct than Bromophenol blue is a better indicator t h a n those either of the others and has the added advantage t h a t used by the other investigators. itris not necessary t o keep a color standard for comThe method has the following advantages: parison. I-It does away with the occasional errors t h a t The soils were digested in 40 cc. of concentrated arise from slight mistakes in measuring the sulfuric sulfuric acid containing I g. of salicylic acid in each acid into the receiving flask. 2 5 cc. The soil is allowed t o digest half an hour a t 2-As t h e boric acid solution.need be measured only room temperature, then 0.5 g. of iron or zinc dust is approximately, much time can be saved, and a n unadded, and after standing half an hour longer j g. of skilled helper can measure i t into the receiving flasks. 3-By proper adjustment of the strength of the standLipman's sulfate mixture1 is added and the digestion, completed over the flame. After digestion, when the ard aci'd and the weights of t h e samples taken the persolution has cooled sufficiently, distilled water is added centage of nitrogen can be read directlyfrom the burette. 4-It is necessary t o prepare accurately only one and the liquid contents of the flask transferred t o anothgr Kjeldahl flask and the residue well washed standard solution, i. e . , the sulfuric acid for titrating. with distilled water which is also transferred t o the second flask. The water added should not be much A W I D AND ACCURATE METHOD FOR DETERMINING over 175 cc. One hundred cc. of saturated caustic NITROGEN IN NITRATE OF SODA BY THE MODIsoda and some mossy zinc are then added and the soluFIED DEVARDA METHOD AND THE USE OF tion distilled into boric acid and the distillate titrated THE DAVISSON SCRUBBER BULB1 the same as the distillate from crops. By C. A. Butt Following the procedures outlined, first with the reINTERNATIONAL AGRICULTURAL CORPORATION, ATLANTA,GA. agents employed for crops and for soils, and later with There is among chemists with whom I have come crops and soils, the figures shown in Table I1 were in touch, and especiaIly among those engaged in the obtained. fertilizer industry, a very strong conviction t h a t the usual methods for the determination of nitric nitrogen, TABLE$ 11-NITROGEN FOUND IN CROPSAND SOILS as in the analysis of nitrate of soda, are far from satisTitration Corrected for Less factory for routine work and none too accurate in the Average Weipht Flask Indicator Check SUBSTANCE G. No. cc. cc. cc. hands of the average analyst. Procedures used in the Reagents for Crops.. . . . . . 1 0.10 ... average fertilizer works laboratory should of necessity 2 0.10 ... 3 0.10 ... be both rapid and accurate; moreover, it is very 0.10 ... 0.10 4 Reagents for Soils.. . . . . . . 1 0.40 ... desirable that constant attention be not required. 0.40 2 ... 0.30 3 ... The modified Kjeldahl-Gunning method, which had 0.30 0.35 4 ... been used in our laboratory for several years, pro5.70 Corn Fodder.. ......... 1 1 5.80 5.50 5.60 2 duced fairly satisfactory results, provided considerable 5.55 5.58 5.65 3 time were given t o complete the solution and re11.50 11.40 &orn Fodder.. . . . . . . . . . 2 1 11.50 11.40 2 duction of the nitrate in the salicylic acid mixture. 11.40 11.40 11.50 3 22.35 22.25 Wheat G r a i n . . ........ 1 1 I n addition to this time-consuming procedure, agree22.20 22.30 2 22.20 22.22 22.30 3 ing duplicate determinations have been very difficult 44.60 44.50 Wheat Grain.. ........ 2 1 t o obtain, unless the sample be dried and ground very 44.60 44.50 3 44.45 44.35 2 44.45 fine. Naturally, therefore, our attention was turned 28.25 28.35 Sweet Clover.. ......... 1 1 t o other direct methods. 28.60 28.50 2 28.50 28.42 28.603 The Devarda method, as refined in late years by W. S. Allen2 56.90 Sweet Clover.. ........ 2 1 57.00 56.90 57.00 2 and also E. R. Allen,3 appeared the most promising, as both 57.10 57.00 56.93 3 investigators obtained almost theoretical results. The method Soil No. 1.. ........... 10 1 4.05 3.70 3.65 2 4.00 recommended by W. S. Allen, while very accurate, necessitated 3.75 3 3.70 4.IO the use of the modified Knorre apparatus which was rather elab4.20 4.55 Soil No. 2............. 10 1 4.40 4.05 2 orate and more complicated as to operation than seemed desirable. 4.50 4.15 3 4.13 The procedure outlined by E. R. Allen for nitric nitrogen in soil extracts, which he designated as the Volmari-MitscherlichI n tests with an ammonium sulfate solution i t was Devarda method, seemed more suitable in that the reduction found t h a t when 50 cc. of 4 per cent boric acid solution and distillation were effected in a very dilute alkali solution were used 95 mg. of nitrogen as ammonia could be re- which permits the reaction to proceed quietly, a distinct adcovered with accuracy. This result was obtained 1 Presented before the Fertilizer Division a t the 58th Meeting of t h e without the use of glycerin which Adler recommends. American Chemical Society, Philadelphia, Pa., September 4, 1919. 1
R z S O I ,20 parts; FeSOa, 2 parts; CuSO+ 1 part.
8th Intnn. Congr. A g g L Chem., 1 (1912), 19. THISJOURNAL, 7 (1915), 521.
