T H E J O U R N A L OF J N D U S T R I A L A N D ENGTNEERING C H E M I S T R Y
344
acetate extract of the yellow-gray silt loam as shown in Table XIII. TABLEXIII-DISTILLATIONOF A POTASSIUM ACETATEEXTRACT OF ACID SOIL, AND OF STOCKSOLUTION OF POTASSIUM ACETATE ( A c i d i t y in Terms of 0.04 N B a s e ) Potassium Acetate Potassium Acetate Extract--Stock Solution-Distillate Residue Distillate Residue 72.9 Cc. 21.9 Cc. 8.6 Cc. 1.95 c c .
AN
--
Phenolphthalein was used as an indicator. This experiment shows the presence of appreciable quantities of acetic acid in the soil extract. About threefourths of the acid shown by the extract was distilled over. Walter Cruml prepared colloidal aluminum hydroxide by separating the acetic acid by heating, but as there were only traces of aluminum salts carried by the potassium acetate extract2 it can hardly be conceived t h a t the phenomena may be accounted for by the presence of these salts, but rather t h a t there is a n excess of acid. COMPARISON OF CATION AND ANION ABSORPTION
To compare the cation and anion absorption of the yellow-gray silt loam from neutral salt solution a 0.0358 N solution of calcium chloride was allowed t o percolate through 2 0 g. of the soil in t h e apparatus shown in Fig. 2 . T h e extract was analyzed for calcium and chlorine. The calcium was determined in an aliquot portion of the extract which had been freed from iron and aluminum by first precipitating as the oxalate and titrating t h e precipitate with a standard potassium permanganate in the presence of dilute sulfuric acid. The chlorine was determined by the Volhard method3 using 0.04 N solutions. The results are tabulated in Table XIV.
Vol.
12,
No. 4
a-The acidity of the salt extract of a n acid soil is independent of the temperature within the range from z j o t o g o o C. 3-The precipitate formed in titrating the soil extract obtained by the Hopkins method absorbs the indicator t o a marked extent. The end result depends upon the temperature, time, and amount of indicator used. 4-The acidity of the first portions of the neutral salt extracts of an acid soil increases with increase in concentration of the neutral salts. 5-The difference in absorption of calcium and potassium from solutions of their bases b y an acid soil may be accounted for by precipitation effects. 6-There is a marked basic exchange when a neutral salt solution is added t o an acid soil, by which alumina is carried into solution. This, however, does not account for the total acidity of t h e solution. 7-When acid soil is extracted with potassium acetate solution, a portion of acetic acid may be distilled off from the extract, showing the presence of free acid. 8-Exchange of acid radicals when an acid soil is treated with a neutral salt solution was not noted. THE USE OF CUPFERRON IN QUANTITATIVE ANALYSIS1 By G. E. F. Lundell and H. B. Knowles BUREAUOF STANDARDS, WASHINGTON. D. Received September 8, 1919
c,
INTRODUCTION
The increasing use of cupferron (the ammonium salt of nitrosophenylhydroxylamine, CeHs.N.N0.0NH4) for the determination of zirconium in its ores and metallurgical products, as well as for minor purposes such TABLEXIV-ANALYSIS OF FRACTIONS OF EXTRACT OF AN ACIDSOILBY A NEUTRAL SALTSOLUTION TO DFTERMINE CATIONAND ANIONABSORPTION as the separation of iron and titanium from manganese Extract Fractions Calcium Chlorine Acid and aluminum in limestone analysis,2 and other deNormality Normality Normality c c. terminations for which i t has been recommended, 0.0348 0.0046 0.0180 1-50 0.0358 0.0037 0.0314 2-50 makes a review oE the possibilities and limitations of 0.0358 0.0028 0.0332 3-50 0.0358 0.0022 0.0335 4-50 this reagent highly desirable. This paper presents a The cation is absorbed t o a measurable extent, for review of the literature dealing with the use of cupwhich the change in acidity fails t o account. There ferron as a quantitative precipitant, and gives the remust, therefore, have been an exchange of base. sults of many tests which were performed a t this This confirms the fact t h a t there is a basic exchange Bureau in connection with a n attempt t o adapt the cupferron method t o the determination of zirconium regardless of the neutral salt used. (See analysis of in its ores and metallurgical products. potassium nitrate extract.) The anion is absorbed little or not a t all. The slight absorption shown in the first 5 0 cc of extract is probably due t o the wetting of the particles and t o a slight dilution of the extract by moisture in the air-dried soil. A small amount of precipitate was formed in each case upon neutralizing the extract. SUMMARY
I-When normal solutions of potassium nitrate, potassium chloride, sodium nitrate, sodium chloride, and calcium chloride were percolated through an acid soil all gave the same end titrations, using phenolphthalein as a n indicator. This corroborates Hopkins’ statements. 1 Ann.,
89 (1854), 168. Compare Conner, THESJOURNAL, 8 (1916). 35. 8 Ann., 190, 1 .
2
GENERAL PRINCIPLES
Cupferron precipitates are salts in which the ammonium radical of the reagent has been replaced by metals. Precipitations are performed in cold solutions containing free mineral or organic acids. Cold solutions must be employed t o prevent decomposition of the reagent into various organic substances, such as nitrobenzene, and the temperature of precipitation is usually specified as “cooled in ice water.’’ A 6 per cent water solution of the reagent is used and complete precipitation is indicated by the formation of a temporary flash of a fine, white precipitate which redissolves, as contrasted with the flocculent insoluble cupferron Published by permission of the Director of the Bureau of Standards. Private communication from J. A. Holladay, Electro-Metallurgical Co.,Niagara Falls, N. Y. 1 2
Apr.,
1920
T H E 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 C H E M I S T R Y
precipitates. Precipitation is usually immediate and filtration is carried on through paper and cone by means of gentle suction. The wash waters are always cold a n d range from 5 per cent (by volume) ammonium hydroxide for iron precipitates t o I O per cent (by volume) hydrochloric acid for titanium and zirconium precipitates. Ignitions of cupferron precipitates are carried on very carefully in the early stages owing t o excessive liquefaction when wet precipitates are ignited, and t o the heavy liberation of gaseous products from dried precipitates. The ordinary procedure calls for ignition t o oxides, although some variations will be noted in certain methods reviewed below. HISTORICAL
The use of cupferron as a quantitative reagent was recommended originally by Baudischl who showed its application t o the determination of iron in brown iron ore and of iron and copper in nickel ore. He also described t h e properties and behavior of t h e reagent, and enumerated instances where it could be used t o advantage. I t s uses have since been studied by many investigators and i t has been proposed as a quantitative precipitant under varying conditions (often loosely defined in t h e earlier papers) for copper, iron, titanium, zirconium, thorium, and vanadium. For convenience, t h e work done on each of these determinations will be given below under separate headings. Tables of results will not be given unless authors have given definite conditions for precipitation. QUANTITATIVE D E T E R M I N A T I O N S WITH C U P F E R R O N COPPER ( I ) HISTORICAL-Biltz and Hodtke2 found t h a t complete precipitation of copper takes place in weak solutions of hydrochloric acid and in solutions of acetic acid containing sodium acetate, b u t not in the presence of excessive amounts of mineral acids. They washed the precipitate first with water, then with I per cent sodium carbonate solution t o remove excess reagent, finally with water, and then ignited t o oxide. Their data demonstrated a very great accuracy for the method. Hanus and Arn. Soukup3 experienced considerable difficulty in precipitating copper from dilute sulfuric acid solutions but obtained good results when filtration on a gooch immediately followed precipitation. The precipitate was washed with cold water, dried, ignited t o oxide, and reduced with methyl alcohol. Baudisch4 in a second paper dealt with t h e properties of cupferron and gave a method for its preparation. Freseniuss demonstrated t h a t copper can be quantitatively precipitated from acetic acid solution containing ammonium acetate. The precipitate was washed with I per cent sodium carbonate solution, dried, ashed, ignited with sulfur in a Rose crucible in an atmosphere of hydrogen, and weighed as cuprous sulfide. Ckem.-Ztg , 33 (1909), 1298. anorg. Chem, 66 (1910), 426 * I b i d . , 68 (1910), 52. Chem.-Ztg., 35 (1911). 913 8 2. anal. Chem., 60 (1911), 35. 1
*Z
345
Weber1 dealt mainly with t h e technique of the use of cupferron and cited the work of Biltz and Hodtke and of Nissenson.2 Baudisch and KingS reviewed the desirable features of the cupferron method, calling attention to the fact t h a t copper can be quantitatively determined in mineral or acetic acids, and giving directions for the preparation of cupferron. ( 2 ) F A V O R A B L E P R O C E D U R E F O R PRECIPITATION-FOr the determination of copper, high mineral acidity is objectionable, b u t weak solutions of hydrochloric or sulfuric acids are permissible, while acetic acid in sodium or ammonium acetate solutions gives the best results. Cold water is the most satisfactory washing medium, The ignition is usually carried t o oxide, although some authors prefer t o transform the oxide t o cuprous sulfide or metallic copper. (3) S E P A R A T I O N S W H I C H H A V E B E E N
ATTEMPTED.
(a)
Copper f r o m Zirtc-Biltz and Hodtke demonstrated t h a t a very satisfactory separation of copper from zinc could be accomplished in acetic acid solution. Hanus and Soukup tried the separation i n weak sulfuric acid solution and obtained results which were not as satisfactory as those of Biltz and Hodtke. ( b ) Copper f r o m Cadmium-Biltz and Hodtke obtained good separation in weak hydrochloric acid b u t not in acetic acid. Hanus and Soukup performed the separation in weak sulfuric acid solution. ( c ) CopPer f r o m Irolz-Biltz and Hodtke found t h a t a good separation could be secured if the copper-iron cupferron precipitate obtained in weak acid solutions was washed with ammonium hydroxide, which dissolved the copper precipitate and not the iron compound. Fresenius obtained a n excellent separation by precipitation.in acetic acid solution containing ammonium acetate followed by washing with ammonium hydroxide. (4) I N T E R F E R I N G SUssTANcEs-Biltz and Hodtke pointed out t h a t lead, silver, mercury, and tin interfere. Fresenius added bismuth t o the list. To the above list should be added iron, titanium, zirconium, cerium, thorium, tungsten, vanadium, and undoubtedly several other elements. The interference of iron, titanium, zirconium, cerium, and thorium, and possibly lead, mercury, tin, and bismuth can be avoided by treating the cupferron precipitate with ammonia and reprecipitating the dissolved copper by the addition of weak acid. ( 5 ) SUMMARY-The use of cupferron for t h e determination of copper is of classical interest and not of any practical importance. IRON
( I ) H I ~ T O R I C A L - B ~ Upointed ~ ~ S C ~o~u t t h a t iron was precipitated by cupferron as reddish brown flocks,
soluble in ether and in acetone. Biltz and Hodtke6 showed t h a t iron could be precip12.anal.
Chem., 50 (19111, 50.
2
Z angew. Chem., 23
a
THISJOURNAL, 3 (1911). 629. Chem.-Ztg., 33 (1909), 1298. LOC.cil.
4
8
(1911), 969.
*
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
3 46
itated with copper and quantitatively separated from i t by the use of an ammonium hydroxide wash. Fresenius' used Biltz and Hodtke's method with good results in hydrochloric, sulfuric, and acetic acid solutions. He cited practical tests of the method with excellent results in the analysis of a manganese ore and the analysis of a ferromanganese. Nissensonl used the reagent for the separation of iron from nickel and cobart in speiss. Ferrari2 published a paper on t h e rapid determination of iron in the presence of soluble organic substances. He showed t h a t quantitative determinations of iron in this class of material can be carried out in 1.5 hrs. by direct precipitation with cupferron of the chlorine-treated hydrochloric acid solutions of the organic material, followed by filtration of the precipitate and ignition t o Fe203. He stated t h a t such elements as copper, silver, lead, mercury, tin, bismuth, titanium, and zirconium interfere with the determination. (2)
FAVORABLE
PROCEDURE
FOR
PRECIPITATION-
Iron can be precipitated from dilute solutions of t h e mineral acids, hydrochloric, sulfuric, and nitric, and from acetic acid. Complete precipitation has been obtained a t this Bureau in solutions containing 2 0 per cent by volume of sulfuric acid. The precipitate may be washed with cold 2 N hydrochloric acid, ammonium hydroxide, or water. Ignition is carried t o the oxide. , (3) SEPARATIONS WHICH HAVE B E E N ATTEMPTED. (a) Iron from Copper-Biltz and Hodtke obtained perfect separations from copper. See COPPER gc. Fresenius demonstrated the exactness of this method. See COPPER 3c. ( b ) Iron from Manganese-Fresenius carried out perfect separations of these elements in hydrochloric acid solution. ( c ) Iron from Zinc-Fresenius showed t h a t complete separation can be had in dilute sulfuric acid solution. ( d ) Iron from Aluminum and Chromium-Biltz and Hodtke performed this separation in mineral acid solution, and washed the precipitate with 2 N hydrochloric acid, water, ammonium hydroxide, and finaIly water. Fresenius showed that the separation of iron from aluminum and chromium is complete in dilute hydrochloric acid solution. ( e ) Iron from Nickel and Cobalt-Baudisch showed that this separation was satisfactory in hydrochloric acid solution. Biltz and Hodtke also obtained a good separation in mineral acids. Fresenius performed perfect separations of iron from nickel and cobalt in dilute sulfuric acid solution. (f) I r o n from the Alkalies and Alkaline EarthsFresenius showed t h a t no trouble was experienced in carrying out these separations in appropriate dilute mineral acids. (9) Iron from Phosphorus-Fresenius also demonstrated the fact that iron can be completely separated from phosphorus in dilute hydrochloric acid solutions. 1 LOC
cit.
* A n n . chim. applicala, 4 (1915),341.
Vol.
12,
No. 4
(4) IKTERFERING sussTAiicEs-Copper, lead, silver, mercury, tin, and bismuth interfere. This, however, is not serious, since their prior separation by means of hydrogen sulfide is an easy matter. Titanium, zirconium, cerium, thorium, tungsten, vanadium, and undoubtedly several other elements of this analytical group also' interfere. (j) SUmIARY-The determination of iron by the cupferron method does not offer any advantages over ordinary established procedures. This reaction may, however, be of value in certain group separations such as the separation of iron and titanium from aluminum and manganese in limestone analysis as proposed and used by Mr. Holladay.1 TITANIUM
( I ) HIsToRIcAL-Schroeder2
found t h a t titanium could be quantitatively precipitated from acid solutions. Bellucci and Grassi3 showed t h a t cupferron quantitatively precipitated the yellow compound (N0.NC6H60)4Ti,which they ignited to TiOa. Thornton4 demonstrated t h a t this method was one of high accuracy in a solution containing varying amounts of sulfuric acid and tartaric acid as is shown b y Table I. Ti02 Used
EXPI'. No. 9 10 11 12
G.
0.1428 0.1066 0.1064 0.1064
TiOr Found G. 0.1429 0.1069 0.1067 0.1066
T A B I ,I~
HzSOn Tartaric Vol. of 1 : 1 Acid Used Solution cc. G. Cc 5 0.5 200 20 1.5 400 30 2.0 400 40 2.0 400
Error
G.
+0.0001 +0.0003 +0.0003 +0.0002
I n Table I1 will be found t h e tabulation of results obtained in tests along the same line carried on at this Bureau. These show t h a t complete precipitation can be made in solutions containing 40 per cent by volume of concentrated sulfuric acid. TABLEI1
EXPT. TiOz Used No. G. 0.0999 0.0999 0.0999 0.0999 0.0999
1 2 3 4
5
TiOr Found G. 0.0997 0.1000 0.0999 0.1001 0.1002
Error
G. -0.0002 +o 0001 0.0000
.
+0.0002
+0.0003
H&OI Vol. of Per cent Solution by Vol. Cc. 5 400 10 400 15 400 20 400 40 400
Qualitative tests of t h e above filtrates showed n o titanium. Brown5 applied Thornton and Hayden's method t o t h e analysis of titanium and zirconium in baddeleyite and zircon with good results. (2)
FAVORABLE
PROCEDURE
FOR
PRECIPITATION-
Titanium can be quantitatively precipitated from solutions containing as much as 40 per cent sulfuric acid by volume. The presence of tartaric acid causes no trouble. Presumably titanium can also be precipitated from solutions containing considerable hydrochloric, acetic, or tartaric acids. Nitric acid in high concentrations is not permissible on account of its action on t h e reagent. (3) S E P A R A T I O N S W H I C H H A V E B E E N ( a ) Titanium from Aluminum-Bellucci CiL. 2.anorg. Chem., 72 (1911),89. Atti accad. Lincei, [VI 22 (1913),30.
1 LOC.
*
8
4
6
A m . J . Sci., 37 (1914),173, 407. J . A m . Chem. Soc., 39 (1917),2358.
ATTEMPTED.
and Grassi
Apr.,
T H E JOL'RNAL O F I N D U S T R I A L A N D ENGILVEERING C H E M I S T R Y
1920
showed t h a t t h e separation of titanium from aluminum is quantitative. This observation was confirmed by Thornton who found, however, as shown in Table 111, t h a t the separation is sharp only i n highly acid solutions, and t h a t addition of tartaric acid is desirable. TABLE111 EXPT.
No.
TiOn Used
A1203 Used
TiOz Found
- _______
Error
0.1066 0.1066 0.05715 0.0572 0.0575 0.0573 0.1067 0.1068
0.1127 0.1127 0.1127 0.1127 0.1127 0.1127 0.1127 0.1127
0.1179 0.1094 0.0590 0.0577 0.0579 0.0575 0.1072 0.1070
4-0.0113 +0.0028 +o .on 18 i o . 0005 +0.0004 +0.0002 +o. 0005 +o .0002
G.
G.
G.
HzS04 1 : 1 Cc. 5 10
G.
Acid Used
G.
...
5
1.2 1.2 1.2 1.2 1.5 1.5
10 15 20 20 20
Vol of Solution Cc. 200 200 200 200 200 200 400 400
( b ) Titanium from Iron-Thornton accomplished this separation by treating an acid tartaric acid solution of the two with hydrogen sulfide, adding ammonium hydroxide after the iron was reduced, continuing t h e addition of hydrogen sulfide and finally filtering off the iron sulfide. The titanium was then determined in the acidified filtrate. Data are given in Table I V . TABLEI V TiOz Used
EXPT.No. 4 5 6 7
FezOs Used
Error
TiOz Found
G.
G.
G.
0.1428 0.1428 0.1066 0.1063
0.2267 0.2267 0.2267 0.2267
0'. 1424 0.1430 0.1068 0.1061
Mg -0.4 +0.2 +0.2 -0.2
(c) Titanium from Phosphorus-Thornton demonstrated t h a t phosphoric acid was without serious effect in strongly acidified solutions, as shown in Table V. TABLE V TiOz EXPT. Used
No.
G.
'13 14
0.1064 0.1066
PzOs Used
TiOz Found
0.0711 0.0710
0.1071 0.1067
G.
G.
Tartaric - ..~ ._...
Error
G. +0.0007 +O.OOOl
HISO( 1 : 1 Cc. 20 25
Acid Vol. of Used Solution G. Cc. 1.5 400 400 1.5
Experiments carried on a t this Bureau dealing with -the effect of phosphoric acid in cupferron precipitations 8of titanium and zirconium are given in Table VI. ZrOz.TiOn Tar(1 : 1) HzSOa taric Per cent Acid Taken G. by Vol. G. 10 1.0 0.2119 0.2119 10 1.0 10 1.0 0.2119 0.2119 10 1.0
operations, Thornton analyzed some solutions t o which chlorplatinic acid had been added. The data, given in Table VIII, demonstrate t h a t platinum introduced into solutions by fusion operations is without effect. TABLEVI11
EXPT
Tartarir
No. 21 22
'
Ti02 Used
G.
Pt Used (approx)
TiOz Found
Error
0 01 0 01
0 1071 0.1066
$ 0 0004 -0 0001
0.1067 0 1067
G.
+0.0007 +O.OOlO -0.0002 +0.0003
G
G.
&SO4 1 : 1 cc. 40 40
VOl of Solution cc 400 400
TABLE IX TarVol. of ZrO,.TiOz HaB03 taric ZrOt.TiOz &So4 SOlUEXPT. 1 : 1 Taken Acid Found Error 1 : 1 tion No. G. G. G. G. G. Cc. Cc. 1 0.2104 0 5 1 0.21061 4-0 0002 40 400 2 0.2104 0.5 1 0.21031 -0.0001 40 400 1 Cupferron filtrate contained neither zirconium nor titanium
(g) Titanium from Alkali Salts-Tests made a t this Bureau dealing with the effect of alkali salts confirmed the observation of Thornton and Hayden' concerning their effect in zirconium precipitations, namely, t h a t the presence of excessive alkali causes high values and the obvious remedy when they are present is t o carry out a preliminary precipitation with ammonium hydroxide, followed by solution of the precipitate in acid and precipitation by cupferron. ( h ) Titanium from Silica-Experiments performed at this Bureau are listed in Tab1.e X, which shows t h a t the separation of titanium (and zirconium) from silica is not complete. This is not a source of trouble, for silica in the final ignited precipitate can be volatilized with hydrofluoric acid with no loss of titanium (or zirconium) provided sufficient sulfuric acid is present.
_.
Error
G.
(f) Titanium from Boric Acid-Since borax was used a t this Bureau for the fusion of several ores, tests were carried out which showed t h a t boric acid was without interfering action. The data obtained are given in Table I X .
TABLEX
Anorox Amount of Soluble Silica in Solution when Treated EXPT. with Cupferron h-0. G. 1 0.05 2 0.05 3 0.05
TABLEV I Weight of PzOs Used Ignited G. Oxide. G. 0.2126 0.02 0.05 0.2129 None 0.2117 None 0.2122
347
VOl. Solution cc. 400 400 400 400
Weight Ignited Cupferron Ppt. ZrOz-TiOz-Si02
G.
0.1651 0.1978 0.2107
.
Weight of Si02 in Precipitate
G.
0.0036 0.0013 0.0006
The results show a contamination greater than t h a t .obtained by Thornton and this is directly attributable t o zirconium, which forms more insoluble phosphates. (d) Titanium from Iron, Aluminum, and Phosphorus -Thornton separated iron, first, by precipitating the reduced iron by ammonium sulfide in ammonium tartrate solution as outlined in b, and then proceeding as indicated in Table 111. The accuracy of t h e method is shown in Table VII.
(i) Titanium from Vanadium-Tests performed a t this Bureau demonstrated t h a t it is not possible t o separate titanium (and zirconium) from vanadium in either the quadrivalent or quinquivalent state. It will be noted t h a t the separation is more nearly complete when vanadium is in the quadrivalent state, and it may be safely stated t h a t contamination varies inversely as the acidity. Table X I gives t h e data obtained.
TABLE VI1
TABLE XI
Ti02
EXPT. Used No. 15 16 17 18 19 20
G.
0.1065 0.1066 0.1065 0.1067 0.1066 0.1066
FenOa Used
G.
0.2036 0.2036 0.1018 0.1018 0.2267 0.2267
A1208 Used
G.
0,1127 0.1127 0,1127 0.1127 0,2254 0.2254
(e) Titanium from
PzOs Used
G.
0.0154 0.0151 0.0153 0.0153 0,0153 0,0153
Ti02 Found
G.
0.1070 0.1068 0.1067 0.1069 0.1069 0.1073
.
Vnl
Tarof HnSOd taric SoluError 1 : 1 Acid tion G. Cc. G. Cc. 30 2 400 +0.0005 30 2 400 +0.0002 40 2 400 +0.0002 400 40 2 +0.0002 +0.0003 40 2 . 5 400 +0.0007 40 2 . 5 400
Platinum-Since platinum is &often introduced into titanium solutions by fusion
cent TarZrOz.Ti0 b y taric VzOs Vol- Acid Taken G. ume G. G. 0.2120 10 None 10 None 0.2120 10 None 0.2120 10 0.2120 None 10 0.2120 0.02 0.05 10 0.2120
EXPT. Taken No. 1 2
3 4 5 6 1
A m . J . Sci., 88 (1914), 137.
Weight of Vto4 Vol. of Cupferron Taken Solution Ppt. G. Cc. G. 400 0.2117 None 0.2122 400 None 400 0.2130 0.02 400 0.2161 0.05 400 0.2270 None 0.2489 400 None
Error
G.
-0.0003 +o .0002 +o ,0010 +0.0041 +0.0150
+0.0369
T H E 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 C H E M I S T R Y
348
The presence of vanadium in both the cupferron precipitates and in the cupferron filtrates was qualitatively established in Expts. 3, 4, j, and 6. The use of ammonium hydroxide wash solution does not lessen the contamination. ( j ) Titalzium from Uranium-Since i t was considered likely t h a t some zirconium steels might contain uranium, tests were made a t this Bureau t o establish the effect of uranium in the cupferron precipitation. The data given in Table XI1 demonstrate that uranium does not interfere when in the sexivalent state, but does interfere in the quadrivalent state. TABLEXI1 Has04
Per cent TarWeight 2rOa.TiOa by taric UOs UOa Vol. of Cupferron EXPT. Taken Vol- Acid Taken Taken Solution No. G. ume G. G. G. cc. 10 1 None None 400 0.2114 1 0.2114 400 None 0.02 0.2122 10 1 2 0.2114 400 0.2179 10 1 None 0.05 3 0.2114 400 0.2118 10 1 0.02 None 4 0.2114 10 1 0.05 None 400 0.2116 5 0.2114
%'?
.
Error
G.
0.0000
+O.OOOS
+0.0065 +0.0004 +0.0002
Qualitative tests showed the presence of uranium in both precipitates and filtrates in Expts. 2 and 3 and no uranium in the precipitates in Expts. 4 and j. ( k ) Titanium from Tulzgsten-The data given in Table XI11 show t h a t tungsten interferes seriously in the precipitation of titanium (and zirconium) by cupferron. TABLEXI11 Per cent ZrOz.Ti0a by EXPT. Taken VolG. No. ume 1 0.2114 10 2 0.2114 5 3 0.2114 20
Tartaric Acid
G..
None None None
Weight of WOa Vol. of Cupferron Ppt. Error Taken Solution cc. G. G. G. 400 None 0.2114 0.0000 400 0.2663 +0.0519 0.1266 400 0.3043 -I-0.0929 0.1286
The ignited oxides in Expts. 2 and 3 were pale blue in color and contained tungsten. It was found t h a t the use of an ammonium hydroxide wash solution markedly lowered the contamination but did not completely eliminate it. (I) Titanium from Thorium-The experiments performed a t this Bureau and given in Table XIV demonstrate that it is not possible to separate titanium (and zirconium) from thorium by the cupferron method. TABLEXIV
EXPT. No.
1 2 3 4
His04 Per cent TarZrOa.TiOz by taric ThOz Vol- Acid Taken Taken G. ume G. G. None 0.2114 10 1 0.02 0.2114 10 1 0.05 0.2114 10 1 10 1 0.20 0.2114
Vol..of Solutlon Cc. 400 400 400 400
Weight of Cupferron Ppt.
G.
0.2116 0.2181 0.2288 0.2734
Error G. +0.0002 +0.0067 +0.0174 +0.0620
Cerium-Quadrivalent cerium interferes markedly in a cupferron precipitation of titanium (and zirconium) while trivalent cerium interferes but slightly. Data obtained in these separations are given in Table XV. Per cent TarZrOa.Ti02 b y taric EXPT. Taken Vol- Acid No. G. ume G . 1 0.2114 10 1 2 0.2114 10 1 3 0.2114 10 1 4 0.2114 10 1
TABLEXV
CeaOs Taken
G. None None 0.02
0.05
CeOa Vol.of Taken Solution G. Cc. 0.02 400 0.05 400 None 400 None 400
Weight of Cupferron Ppt. Error
G.
G.
0.2140 0.2139 0.2121 0.2130
+0.0026
+0.0025 +0.0007
+0.0016
12,
No. 4
(4) I N T E R F E R I N G SUBSTANCES-It Will be noted from the foregoing review t h a t there is a formidable array of interfering elements. These may be divided under five heads, as follows: (a) Interfering elements removable by a preliminary ammonium hydroxide precipitation. Alkalies, alkaline earths, and copper (incompletely) are in this class. ( b ) Interfering elements removable by hydrogen sulfide in acid solution. 'These are copper, lead, silver, mercury, tin, bismuth, and other likely interfering elements of the hydrogen sulfide group. (c) Interfering elements removable by ammonium sulfide in ammonium tartrate solution. Iron is the chief element, although this treatment also removes other elements, such as nickel, cobalt, and manganese. ( d ) Interfering elements removable by the use of an ammonium hydroxide wash. Copper is the chief interfering element of this class. The interference of tungsten and vanadium is lessened by this treatment. ( e ) Interfering elements not removable. This list includes zirconium, thorium, cerium in the quadrivalent state (less in the trivalent condition), uranium in the quadrivalent condition (but not in the sexivalent state), tungsten, vanadium in either quadrior quinquivalent condition, and silica. Phosphorus interferes but slightly in a I O per cent sulfuric acid solution. (5) svM&IARY-The determination of titanium in, pure solutions by the cupferron method is most exact. The method is subject t o so many interferences t h a t it. loses its value in technical analysis except for certain separations, such as, for example,- titanium from chromium and aluminum which are indicated under (3). ZIRCONIGM
( I ) HIsToRIcAL-Schroederl
stated t h a t zirconium could be quantitatively precipitated by cupferron in acid solutions. Thornton and Hayden2 demonstrated t h a t tFie determination could be carried out in solutions containing from 5 t o 7 . 5 per cent by volume of sulfuric acid. Ferraris also showed t h a t zirconium could be quantitatively determined in acid solution by means of cupferron. Brown4 applied the method described by Thornton and Hayden t o the analysis of zircon and baddeleyite with excellent results. Tests, which are given in Table XVI, carried on a t the Bureau of Standards, show t h a t zirconium can be quantitatively precipitated in solutions containing 40 per cent by volume of sulfuric acid and t h a t tartaricacid is without effect.
( m ) Titanium from
&SO4
Vol.
TABLEX V I HzSOi ZrOa Per cent Tartaric Vol. of
ZrOi
N o . Added G. Volume by Acid G. cc. Found G. 0.1118 5 None 400 1 0.1118 0.1117 400 2 0.1118 10 None 0.1120 15 None 400 3 0.1118 400 0.11231 4 0.1118 20 None 40 None 400 0.11231 5 0.1118 5 1 400 0.1116 0.1118 6 10 5 400 0.1117 7 0,1118 1 Ignited precipitates contained traces of SOX. 1
Z. anoyg. Chem., 73 (1911),89.
* A m . J . Sci., 88 (1914), 137. I Ann. 1
chim. apfilicala, 3 (1914), 276. J . A m . Chenr. SOC.,S9 (1917), 2358.
Error G. 0.0000
-0.0001 +0.0002 +0.0005 +0.0005
4.0002 4.0001.
Apr.,
T H E J O U R N A L Q F I N D U S T R I A L A N D E N G I N E E R I N G C HE,MIS T R Y
1920
(2) F A V O R A B L E P R O C E D U R E F O R PRECIPITATION-The conditions given under TITANIUM 2 , governing t h e precipitation of titanium, apply directly t o zirconium. (3) SEPARATIONS WHICH HAVE B E E N STUDIED. (a) Zirconium from Aluminurrt-Data obtained b y Thornton and Hayden are given in Table XVII and show a satisfactory separation.
z'ro,
EXPT. Taken No. 1 2 3 4
TABLEX V I I ZrOz Taken Found G. G. 0.1127 0.1090 0.1127 0.1090 0.1127 0.1090 0.1127 0.1094 ~ 1 2 0 ~
G.
0,1091 0.1088 0.1086 0.1091
Error Mg. -0.1 +0.2
+0.4 $0.3
1 : 1 Cc. 40 40 60 60
VOl. Of Solution Cc.
400 400 400 400
( b ) Zirconium from Iron-The above authors applied the tartrate ammonium sulfide separation of iron, followed b y cupferron precipitation of zirconium, and obtained excellent results as shown in Table
XVIII. ZrOz EXPT. Taken
No. 5 6
G.
0.1088 0.1090
Fez03 Taken G. f 0.1018 0.1018
TABLEX V I I I ZrOz Found G. 0.1091 0.1093
Error Mg. +0.3 +0.3
HzSO4 Tartaric 1 : 1 Acid Cc. G. 40 2 40 2
(c) Zirconium from Phosphorus-Thornton and Hayden claimed t h a t this separation was not feasible. Experiments carried on a t this Bureau and also b y Mr. Holladayl demonstrated t h a t fair separations are possible if the acidity is high, I O per cent sulfuric acid by volume, and the concentration of phosphorus pentoxide is not higher t h a n 0 . 0 2 g. per 400 cc. of solution. Higher concentrations of phosphorus pentoxide require prior removal, or analysis and correction of the weighed precipitate. Table X I X gives d a t a obtained a t this Bureau. TABLEXIX ZrOz P2Ob Tartaric Weight EXPT. Taken Taken Acid of Ppt. No. G. G. G. G. None 0 1151 1 0.1118 0.01 1 0:1135jA 2 0.1118 0.01 3 0.1118 0.02 None 0 1123 0:1121)B 5 4 0.1118 0.02
Has04 Vol.of Per cent SoluError by tion G. Volume Cc. +0.0033 5 400 +0.0017 5 400 +0.0005 10 400 +0.0003 10 400
Qualitative tests showed considerable phosphorus pentoxide in A and traces in B. ( d ) Z i r c o ~ ~ i ufrom m Iron and Aluminum-Thornton and Hayden obtained very satisfactory separations of these elements, as shown in Table X X , by first separating the iron as described in b above and then the aluminum as in a. TABLEXX ZrOz EXPT.Taken No. G. 7 0.1087 8 0.1089 9 0.1101 10 0.1100
FezOa Taken
G.
0.1018 0.1018 0.2036 0.2036
AlzOa Taken G. 0.0564 0.0564 0.1127 0.1127
ZrOz Found G. 0.1086 0.1088 0.1110 0.1103
TarVOl. of taric HzSOa SoluError Acid 1 : 1 tion Mg. G. Cc. Cc. -0.1 2 40 400 -0.1 2 40 400 4-0.9 2 40 400 +0.3 2 40 400
( e ) Zirconium from Platinum-The observation of Thornton concerning t h e effect of chloroplatinic acid on a cupferron precipitation of titanium, which is given under TITANIUM 3e, will undoubtedly hold true for zirconium. cf) Zirconium from Boric Acid-See TITANIUM 3f. (g) Zirconium from Alkali Salts-Thornton and Hayden gave data, tabulated in Table X X I , which 1
Private communication.
349
show t h a t moderate excess sf ,alkali causes no difficulties. ,See also T I T A N ~ U M 3g.. TABLE XXI
EXPT. No. 11 12
ZrOz Taken
KzO Taken
0.1088 0.1089
2.7027 2.7027
G.
G.
ZrCh Found G. 0 1097 0.1096
Error ME. +019 +0.7
&SO4
1 : 1 Cc. 40 40
vol. O f
Solution Cc. 400
400
( h ) Zirconium from Silica-See TITANIUM 3h. (i) Zirconium from Vanadium-See TITANIUM 3i. ( j ) Zirconium from Uranium-See TITANIUM 3j . ( k ) Zirconium f r o m Tungsten-See TITANIUM 3k. ( I ) Zirconium fro* Thorium-See TITANIUM 31. (m) Zirconium from Cerium-See TITANIUM 3m. (4) I N T E R F E R I N G SuBsrANcEs-The elements which interfere with titanium also interfere with zirconium, except phosphorus which exercises a greater disturbing effect. The methods of removing the interfedng elements also apply t o zirconium. ( 5 ) SUMMARY-The determination of Birconium in pure solutions by the cupferron method is most exact. The method is subject t o so many interfering elements t h a t i t loses much of its value in technical analysis. The d a t a given in this chapter demonstrate t h a t t h e ignited and weighed cupferron precipitate must be most carefully tested in order t o make certain of its true composition. THORIUM
( I ) HIsToRICAL-Thorntonl found t h a t precipitation of thorium by cupferron is incomplete in the presence of even a small excess of sulfuric acid. This observation was confirmed a t this Bureau. The d a t a given in Table XXII were obtained by Thornton by precipitation in acetic acid solution and by the use of a one per cent ammonium acetate wash. TABLEXXII EXPT.
ThOz Used
ThOz Found
1
0.0925 0.0923
0,0924 0.0917,
No. 2
G.
G.
Error
G.
-0.0001 -0.0006
AmHzSO4 monium Vol. of (approx.) Acetate Solution 1 : 1 cc. cc. G. 15 500 1.25 15 500 1.25
(2) F A V O R A B i E P R O C E D U R E F O R PRECIPITATION-This is given in Table XXII. (3) S E P A R A T I O N S W H I C H H A V E B E E N A T T E M P T E D . (a) Thorium from Iron-Thornton showed t h a t a good separation of thorium from iron could be obtained by the procedure which he used in similar titanium and zirconium separations (see TITANIUM 3b and ZIRCONIUM 3 b ) and gave the data presented in Table XXIII.
TABLEXXIII AmmoVol. of ThOz Fez03 ThOz niuh SoluAcetic tion Found Error Acetate Used EXPT. Used G. Acid cc. G. G. No. G. G. 25 Concentration 400 3 0.0924 0.1018 0.0922 -0.0002 25 not stated 500 4 0.0924 0.1018 0.0916 -0.0008 25 400 5 0.1846 0.1018 0.1840 -0.0006
(4) I N T E R F E R I N G SUBsTANcEs-The elements listed under titanium (see TITANIUM 4) as interfering affect also the precipitation of thorium, and undoubtedly many more on account of the low permissible acidity. ( 5 ) SUMMARY-The determination of thorium by the use of cupferron is of no practical importance since it is affected by as many interfering elements as an ammonium hydroxide precipitation of this element. 1 Am.
J . Sci., 42 (1916), 151.
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 HCI.. . . . . . . . . . . . . . . 8 . 2 1 cc. N HCI.. . . . . . . . . . . . . . 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.
