Apr., = 9 = 9
T H E JOC'RiVAL O 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 H E M I S T R Y SUMMARY
I-The procedures designated as official for determining total nitrogen including nitric nitrogen are not suitable for studies in soil biology where large volumes of solution must be employed. 11-The presence of much organic matter interferes in t h e reduction by t h e Ulsch method. 111--The reduction of nitric nitrogen in an alkaline solution with Devarda's alloy removes any danger of loss of gaseous nitrogen. IV-The method which has been perfected effects t h e reduction in alkaline solution, t h u s avoiding loss of gaseous nitrogen; dilute alkali is used, and t h e amount of interfering substances in digestion t h u s largely avoided; and by means of a reliable absorbing device escape of ammonia is guarded against. I t possesses t h e added features of ease of manipulation a n d extreme accuracy of results.
311
using 5 cc. of potassium hydroxide solution containing 2 g. potassium hydroxide and 0.8 g. pyro, t h a t 0.4 t o 3 . 4 per cent of carbon monoxide were given off. Calvert' found t h a t 2 t o 4 per cent carbon monoxide were produced when pyro acted upon oxygen. Weyl and Goth2 reached t h e conclusions t h a t t h e absorption was a t a, maximum when t h e soda was sufficient t o form t h e compound CsHs(ONa)s, b u t this is not t h e case when potash is used instead of soda. He recommended 0 . 2 5 g. pyro in I O cc. sodium hydroxide, sp. gr. 1.030. Weyl and Zeitler3 state t h a t t h e maxi-
DIVISIONOF SOIL TECHNOLOGY OHIO AGRICULTURAL EXPGRIMENT STATION WOOSTER, OHIO
e
SODIUM PYROGALLATE SOLUTIONAS AN ABSORBENT FOR OXYGEN1>2 By G. W. JONF,S
AND
M. H. MEIGHAN
I n this report are shown experiments made for t h e purpose of determining t h e feasibility of using sodium hydroxide t o replace t h e more expensive potassium hydroxide in pyrogallate solutions for t h e absorption of oxygen. I n view of t h e high price of potassium hydroxide, due t o t h e war, and t h e inability at times of obtaining it a t all, relief was sought b y using sodium hydroxide.
C
€11 S T 0 RI C A L
A great amount of experimental work has been done b y different investigators along these lines. Of recent date, Shipley8 made exhaustive tests on sodium hydroxide as a substitute for potassium hydroxide and concludes t h a t it is as good or superior t o potassium hydroxide, t h a t no carbon monoxide is given off, a n d t h a t t h e rate of absorption is proportional t o t h e concentration of t h e pyro. Anderson4 criticizes t h e solutions recommended b y Shipley as being too viscous, and states t h a t expense saved in cost of material is more t h a n offset by t h e time lost for complete absorption and t h e extra amount of manipulation. LiebigO was one of t h e first t o make use of potassium pyrogallate for absorbing oxygen. He found from experiments t h a t I g. of pyro in ammoniacal solutions absorbed 0.38 g. of oxygen or 260 cc., and I g. pyro in a potassium hydroxide solution absorbed 189. T h e strength of t h e ammoniacal or potassium hydroxide solution is not stated. He also tested gallic and tannic acid as a n absorbent b u t found them very slow as compared t o pyro. Boussingault6 found when Published by permission of the Director, Bureau of Mines. Read at the 56th Meeting of the American Chemical Society, Septem ber 10 to 13, 1918. 8 J . A m . Chem. Soc., 38 (1916), 1687 4 THISJOURNAL, 7 (19151,587; 8 (1916). 999. 6 A n % , 17 (1851), 107. Comp:. rend., 57 (1863),883. 1
2
FIG. 1 -RELATIVEABSORPTION OF LIQUIDS TESTING APPhR4TUS
mum absorplion was obtained with potassium hydroxide (of specific gravity 1.05, and t h a t 1.50 is too strong. Lewes4 states t h a t freshly made pyro solution must not be used, t h a t it should stand 24 hrs. After t h e solution had been used for some time carbon monoxide was given off. Clowes5 found t h a t carbon monoxide was given off unless there was excess of potassium hydroxide. He recommends a solution of 160 g. potasstum hydroxide a n d I O g. pyro in zoo cc. water. This solution will not give off carbon monoxide even when analyzing pure oxygen. Bertheloto states 1
Ann., 130 (1864), 248.
* Ber., 14 (1881), 2659.
* A n n . , 205 (lSSO),255. 4 J . SOC.Chem. Znd., 10 (1891), 407. 5 I b i d . , 15 (1896),742. 6
Compt. Tend., 126 (1898), 1066.
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
312
Vol.
11,
No. 4
TABLE I
TEST
Vol. of
No. 1
.............
2 3
cc.
.............
.............
5 10
............. 5 .............
............ .............
6.
............. 9 ............. 8
............. 11 ............. 12............. 13 ............. 10
cc. 25 A 25 A 25 A 25 A 25 A 25 A 25 A 25 A 25 A 25 B 25 B 25 B 25 B 25 B 25 B 25 B 25 C 25 C 25 C 25 C 25 c 25 c 25 D 25 D 25 D 25 D 25 D 25 D 20 D 20 D
2 2 2 5
4
7
Soln.
VOl. of Pyro
5
10
10 2 2 5 5 5 10 10 2 2 5 5 10 10 2 2 5 5 10 10 15 15
1
Min. Mm. 26 26 26 40 48
50 32 32 33 16 15 34 20 24 32 32 29 29 43 45 66 60 47 48 55 63 80 83 54 57
2 Min. Mm. 35 36 36 61 58 67 53 52 53 26 24 42 36 41 61 58 48 48 74 79 103 99 71 69 98 97 117 120 94 100
3 Min. Mm 40 42 42 76 75 78 75 65 74 34 34 58 50 56 83 80 60 62 94 99 119 118 87 85 115 113 127 128 113 113
4 Min. Mm. 46 50 48 88 86 88 88 84 92 41 41 76 62 68 98 96 72 73 106 113 126 126 99 99 125 122 130 130 121 122
5 Min. Mm. 52 54 54 96 96 96 98 97 103 48 48 82 73 78 111 110 82 85 118 122 130 130 108 109 130 127 130 130 125 125
t h a t pyro mixed with more t h a n three equivalents of potassium hydroxide gave off carbon monoxide equivalent t o '/75 t h e oxygen absorbed, the absorption is constant between t h e temperatures of 15" C. t o 62' C., using from I t o 3 equivalents, and with equivalent t h e absorption is reduced and t h e carbon monoxide increased. The solution recommended is as follows: 3 2 g. pyro in I O O cc. water mixed witl, 3 or more equivalents of potassium; strength of potassium hydroxide not stated.
6 Min. Mm. 56 58 58 103 104 102 106 112 112 54 54 89 83 88 119 119 90 93 125 128 132 132 115 115 132 130 130 130 126 127
7 Min. Mm. 61 64 65 110 113 108 114 117 120 58 60 96 92 96 128 127 97 101 130 130 132 132 120 120 134 131 130 130 127 128
8 Min. Mm. 66 69 70 116 118 114 120 124 125 64 65 104 98 104 133 132 103 105 134 134 132 132 125 124 134 132 130 130 127 128
9 Min. Mm. 70 73 76 120 123 120 124 131 113 70 70 108 104 110 138 136 108 110 136 135 132 132 127 126 135 132 130 130 128 130
d;.
Mm. 74 78 82 123 127 124 128 135 136 74 74 114 110 116 140 138 112 115 138 136 132 132 129 129 135 132 130 130 129 130
CO PdClz Per cent Test
.... .... 0.00
Neg.
0.00
Neg.
6:ab
Nee.
.... ....
....
.... 0.00 ....
a:&i
....
0
or!
.. .. .. ..
.... ....
Oxygen Absorbed
cc.
Not me'asured
....
....
Neg.
....
Neg.
.
>; ,
.
...
0.13
k'0-S
0.08
Pos.
0.11
POS.
.... .... ....
0.31
....
.... .... Pos.
....
63
0.15
Pos.
.... 62
0.11
Pos.
61
.... ....
....
0.16
....
....
.... Pos.
.... .... 62
plied by forcing air into t h e bottle through t h e threeway cock a , t h e n closing a and noting any pressure drop. After t h e bottle had been found leak-proof t h e desired amount of pyro solution was introduced by means of the funnel and three-way cock a, b y blowing on rubber t u b e f. Immediately after t h e pyro had
E XPE RI M E NTA L
The ideal solution should absorb rapidly, not be too viscous, and above all, should not give off appreciable quantities of gases such as carbon monoxide. Where analyses are made t o a n accuracy of 0.01t o 0 . 0 2 per cent if only a trace of carbon monoxide is given off, these solutions could not be used. Reagent 9, recommended b y Shipley as most suitable for gas analysis, was found t o be too viscous, and after a short time readings could not be made when used on Haldane apparatus. Tests were made with sodium hydroxide from t h e highest concentration t o very dilute and with varying amounts of pyro. Very accurate tests were made for carbon monoxide produced with different solutions. This is more important for accurate mine air analysis t h a n rapidity of absorption. To test t h e relative absorption of t h e different solutions, t h e authors devised t h e apparatus shown in Fig. I . The relative absorption could be read b y the reduction of pressure on t h e manometer per minute. By using approximately t h e same amount of solution and using t h e same procedure of shaking, t h e relative absorption could be determined directly from curves plotted against pressure and time. T o make a test t h e sodium hydroxide solution was introduced by removing t h e rubber stopper g. After t h e sodium hydroxide had been added t h e bottle was tightly stoppered; heavy cylinder oil on t h e stoppers helped t o prevent leaks. To test for leaks pressure was ap-
FIG.2-BURETTE
AND
ABSORPTION PIPETTE FOR GAS LABORATORY
been introduced t h e three-way cock a was turned 180" t o connect with d , leading t o t h e air t o allow t h e pressure in the bottle t o become atmospheric. Cock a was then closed b y turning through 90° a n d readings of pressure taken every minute on the manometer c for I O min. while t h e apparatus was given uniform shaking b y sliding t h e bottle back and forth on
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 C H E M I S T R Y
APr., 1919
Vol. of Pyro
SOLN.
No.
cc.
3
10 1 g. Pyro 3 cc. He0
]
10 1 g. Pyro ( 3 c c . Ha0
1
{ 6
Shipley’s No. 9
i
Vol. of NaOH cc. 25 Sp. gr. 1.49
10 g. Pyro 7.36g.NaOH 11.62 35 CC. Ha0
35
K Pyrogallate 1 2 0 g KOH 80 cc. HzO 5 g. Pyro 15 cc. Hz0
25 Sp. gr. 1.30
I
......
......
TABLEI1 Vol. 0 2 abTime sorbed, Cc. Min. 100 9 100 14 100 15 100 26 100 (air) Sample left 86.6 cc. 100 8 l/a 100 11 100 14 100 19 100 (air) SamDle left for CO 94.2 CC. 100 9 100 9’/2 100 12 100 15 100 13 100 14 100 15 100 14’/z 100 13 100 16 100 111/1 100 (air) 100 25 100 Incomplete in 1 hr. (56.6 cc. left)
313
co
REMARKS Produced 0.03 cc. from 400 cc. 0% Solution rather viscous but did not gum capillary tubes. Very dark and rather difficult to see through film on the glass. Meniscus could be easily read PdClz+ 0.04 cc. CO from 400 cc. Oa
Solution less viscous than above soln. Very dark and difficult to see through film on glass. Easy to read meniscus
PdCla1.48 cc. CO formed after absorbing 1100 cc. 0 2
Solution very rapid with a high specific absorption but too viscous t o use in our pipettes. Also i t is very dark, and as i t sticks t o the walls of the pipette i t is impossible to accurately read the meniscus in any of our pipettes
About 0.51 cc. CO formed absorbing 243 cc.
Pyro used by Bureau of Mines. according t o Hempel
Made
(
a table at a uniform rate. By introducing t h e solutions separa.tely and just a t t h e moment of making an analysis, there was no absorption of oxygen before making a test. A thermometer, e, indicated any rise of temperature due t o t h e reaction of pyro and sodium hydroxide. For very high concentrations of pyro t h e heat given off is considerable and other methods are necessary. I n t h e results obtained in this table, t h e temperature was kept near 2 0 ’ C. and in no case did t h e heat of reaction cause t h e gas t o rise over 3’ C. TABLE 111-SHOWING THE RELATIVE AMOUNT OF NaOH A N D H10 U S E D GRAMSA K D PER CENT OF CO FORXED IN EACHTEST SOL T IT IoN Pyrol NaOH Hi0 co No. 1
G. G. 17.12 0.54 17.12 1.35 17.12 2.70 9.10 0.54 9.10 1.35 9.10 2.70 4.68 0.54 4.68 1.35 4.68 9 2.70 10 0.54 2.78 11 .......... 1 . 3 5 2.78 2.70 12.. 2.78 13 . . . . . . . . . . 4 . 0 5 2.22 1 Used sp. gr pyro as 1.08.
.......... 2 .......... 3 .......... 4 .......... 5 .......... 6 .......... 7 .......... 8 ..........
.......... .......... ........
G. 21.75 24.18 28.23 25.02 27.45 3 1 .50 29.19 28.62 31.67 26.59 29.02 33.07 32.13
IN
T o test for t h e presence of carbon monoxide after t h e oxygen absorption was complete, mercury was added through t h e funnel 6 and three-way cock a until t h e pressure on t h e manometer was zero. I n this way t h e amount of oxygen absorbed could be determined by measuring t h e mercury added. T h e gas was then transferred t o a gas apparatus for the exact analysis of carbon monoxide. Burrell’s modification of t h e Haldane apparatus‘ was used in these tests. A little over 15 cc. were introduced into t h e burette and accurately measured, t h e n air added until t h e total volume equaled about 2 0 cc. and again measured;
Per cent Negative Negative Negative Negarive Negative Negative 0.13 0.08 0.11 0.31 0.15 , 0.11 0.16 ~~
~
In t h e following tests t h e pyro used was made in t h e proportion of j g. pyro t o I j cc. water. Sodium hydroxide solutions were as follows: Solution A commercial stick sodium hydroxide and water in equal amount b y weight. The sodium carbonate present was filtered o f f by suction over glass wool; resulting solution had a specific gravity 1.49 or 46 per cent sodium hydroxide. Solution B, sp. gr. 1.30, or 28 per cent sodium hydroxide. Solution C, sp. gr. 1.17, or 16 per cent sodium hydroxide. Solution D, sp. gr. 1.11, or I O per cent sodium hydroxide. Solutions B, C, and D were made by diluting A. Table I shows results of using different amounts of pyro with different concentrations of sodium hydroxide over a wide range of concentration varying from concentrated solutions t o those containing only I O per cent sodium hydroxide. All tests were made in duplicate, or triplicate, if necessary t o check.
I
2
9
4
5
6
7
6
9
IO
M1NUrE.S
CURVE 1
next t h e carbon monoxide was burned b y t h e slow combustion method. From the contraction and carbon dioxide produced the percentage of carbon monoxide was determined: z C 0 0 2 = 2C02. The carbon
+
For description and method of use, see Bureau of Mines’ Bulletin 43, “The Sampling and Examination of Mine and Natural Gas,” by G . A. Burrell and F. M. Seibert.
314
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 C H E M I S T R Y
V O ~11, . NO.4
140 I30
1.90
120
MINUTPS
CURVE2
monoxide is equal t o twice t h e contraction or equals the carbon dioxide produced. Analyses were made on one determination of each test and were checked t o o.oI per cent. ~ 1 1 tests showing carbon monoxide were confirmed by t h e palladium chloride test whereby metallic palladium is precipitated in t h e presence of carbon monoxide. were made by averaging t h e The following readings in Table I. Curves I , 2, 3, and 4 show averages of tests made with constant amounts of sodium hydroxide a n d varying amounts of pyro 'and water. All solutions used in Curves 3 and 4 gave off small amounts of carbon
monoxide. Curves 5, 6,a n d 7 show a combination of t h e above, using the Same amounts of pyro and varying amounts Of sodium hydroxide and water. From t h e curves i t is evident t h a t t h e rate of absorption increases with t h e dilution of t h e sodium hydroxide, and for any given sodium hydroxide solution increases with t h e concentration of pyro. T h e most rapid sodium hydroxide solutions gave off carbon monoxide, therefore are not suitable for oxygen absorption. Further tests were made on t h e two most promising solutions, Nos. 3 and 6, using apparatus shown in Fig. 2. The Pipette was made t o hold 3 5 cc. of solu-
9
c
2
$
4 4
s
I
2
S
4
E
6
MINUTES
CURV1:
5
.
7
6
8
10
Apr.3 1919
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 C H E M I S T R Y
315
140
nI M I N U TEES CURVE
6
tion and was filled with small glass tubes. The solutions were introduced as follows: Nitrogen was passed through a b y way of stopcock b for some time t o displace all t h e air, then 2; cc. of t h e sodium hydroxide solution added and t h e required amount of t h e pyro solution and t h e pipette immediately closed with a rubber bag not shown in t h e drawing. This also had been previously filled with nitrogen. These tests were made t o determine how t h e solutions behaved in actual operation: First, with regard t o t h e absorption of oxygen of high and low percentages; second, how much carbon monoxide was given off under different conditions; third, ease in making readings after being used for some time; and fourth, t h e tendency t o foam or clog t h e capillary tubes. Oxygen made from oxone cartridges was used t o exhaust t h e solutions. Then air was added and carbon monoxide determined in t h e residual gas. Table I1 shows t h e composition of t h e solutions, time required for absorbing each I O O cc. of pure oxygen, and quantity of carbon monoxide produced. Of t h e above four solutions, Shipley's No. 9 has b y far t h e fastest rate of absorption, but too large quantities of carbon monoxide are produced for accurate work, and it is so viscous t h a t it is almost impossible t o read t h e meniscus accurately. T h e potassium pyrogallate solution used in t h e above test is t h a t used by t h e Bureau of Mines for absorbing oxygen in mine air analysis and corresponds t o t h a t proposed b y Hempel and is made as follows: 1 2 0 0 g. of potassium hydroxide are dissolved in 800 cc. of water and allowed t o cool. I n a separate beaker 5 0 g. of pyrogallic acid are dissolved in 150 cc. of water making 184 cc. of solution. The potassium hydroxide solution, after cooling, is evenly distributed in 3 j o cc. magnesium citrate bottles and 46 cc. of pyro solution added t o each bottle. The
I I I I I I I I 1
2
~ i iI i i i 3 4
i l i i i i i i i i i i i i i " t i i i i i 1 5
6
7
8
9
IO
MINUTES
CURVE7
bottles are then tightly stoppered by a rubber gasket and thoroughly shaken. By using these quantities enough solution is made t o fill four magnesium citrate bottles and there is no absorption of oxygen during t h e process of making. When using t h e above solutions with air no carbon monoxide was given until they were nearly exhausted, when traces of it were detected by t h e palladium chloride test. I n no case was there found over 0.03 per cent. SUWMARY
A new apparatus for testing t h e relative absorption of oxygen with different solutions has been devised. Tests made over a wide range of concentrations of t h e different reagents show t h a t t h e rate of oxygen absorption in sodium pyrogallate solutions increases with t h e dilution of t h e sodium hydroxide and for a n y given concentration of sodium hydroxide t h e rate of absorption is proportional t o t h e concentration of t h e pyrogallic acid. Sodium pyrogallate solutions made by using sodium hydroxide solutions of less t h a n 1.30 specific gravity give off carbon monoxide which increases with t h e dilution. All sodium pyrogallate solutions give off carbon monoxide when analyzing oxygen samples containing above 95 per cent oxygen. A sodium pyrogallate solution which gives off a minimum amount of carbon monoxide, having a fairly high rate of absorption, and adapted for pipettes, using glass tubes, is recommended. This solution is made as follows: Stick sodium hydroxide is dissolved in a n equal weight of water, and constitutes t h e stock sodium hydroxide solution. I n another container stock pyro solution is made up in proportions of I g. of pyro t o 3 cc. of water. When ready for use, j parts of t h e
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
316
sodium hydroxide solution are mixed with 2 parts of PYro. I n cases where t h e small quantity of carbon monoxide given off is below t h e error of analysis, as when used in the Orsat apparatus, Solution 6 will be found suitable. BUREAUO F MINES WASHINGTON, D. C.
THE DETERMINATION OF URANIUM IN ALLOY STEELS AND FERRO-URANIUM By
G. I. KELLEY,3. B. MYERS AND C. B. ILLINGWORTH Received October 3, 1918
The recent use of uranium in alloy steels has made it desirable t o develop a convenient and reliable method for determining this element in the presence of any of the other elements now in common use in the manufacture of alloy steels. Uranium has been used in t h e manufacture of commercial high-speed steels where i t might be associated with chromium, molybdenum, vanadium, tungsten, and cobalt; and it has been used, experimentally a t least, in steels containing chromium and nickel. I n addition t o t h e elements named above, carbon. manganese, silicon, phosphorus, and sulfur are always present, and aluminum and titanium may be present in small amounts. The method as outlined below provides €or these possibilities. A 2 g. sample is dissolved in 7 5 cc. of I : I hydrochloric acid. After solution is complete t h e solution is oxidized by the dropwise addition of nitric acid. I n t h e case of samples where tungsten is present a n easily filterable product is obtained by diluting t o 300 cc. and boiling for 15 min. T h e tungstic oxide is then filtered out and washed, t h e filtrate and wash waters being returned t o t h e original beaker for evaporation t o dryness, followed by baking a t a moderate temperature. On dissolving the residue with 50 cc. of I : I hydrochloric acid and diluting with hot water, a solution is obtained from which the balance of the silica and the last traces of tungsten can be separated b y filtering. T h e two precipitates after washing are available for the determination of tungsten a n d silicon by t h e usual methods. Filtrates and wash waters from these precipitates are combined and evaporated t o a syrupy consistency in preparation for the extraction of most of the iron with ether. I n the absence of tungsten t h e original solution is evaporated t o dryness and baked with the object of removing silica. After t h e extraction of t h e iron, t h e aqueous layer is evaporated t o a small volume t o free i t from the excess of acid. It is then diluted t o a volume of 1 5 0 cc. with hot water, and a n excess of sodium carbonate in t h e form of a saturated solution is added. This solution IS boiled and, after settling, filtered, the precipitate being washed with hot water. The precipitate consists of the hydroxides of chromium, iron, manganese, cobalt, nickel, copper, and aluminum, if all of these elements are present, together with traces of silica, titanic oxide, phosphorus, a n d vanadium compounds. The filtrate contains uranium, molybdenum, vanadium, and traces of the elements which occur chiefly in the precipitates. Bulky precipitates should be dissolved in hydro-
Vol.
II,
No.
4
chloric acid and reprecipitated one or more times with sodium carbonate solution t o insure a complete separation of t h e uranium. The difficulties from this source are not as great as might be expected. All filtrates from t h e precipitate are cautiously acidified with sulfuric acid and boiled long enough t o insure t h e complete removal of all carbon dioxide. Ammonia free from carbonate is then added in slight excess. Boiling precipitates t h e uranium, much of t h e vanadium, and traces of impurities. The molybdenum is left in t h e filtrate. Steels contain only small amounts of phosphorus and t h e contamination of t h e uranium from this source is usually negligible. When, however, as may occur, t h e amount of phosphorus is large, i t may be necessary t o dissolve t h e precipitate in nitric acid, and after suitable oxidation, precipitate the phosphoric acid with ammonium molybdate. The phosphorus can then be removed as ammonium phosphomolybdate. T h e uranium and vanadium may be reprecipitated from this filtrate along with t h e manganese, if permanganate is used t o oxidize t h e phosphorus, by adding a few drops of sulfuric acid, a s m a l l amount of ammonium persulfate, and enough carbonate-free ammonium hydroxide t o give a n excess. The precipitate obtained by boiling the solution is in t h e condition corresponding t o the first uranium precipitate mentioned above. The impure uranium precipitate containing phosphorus in negligible amounts, o i free from it, is transferred to a beaker with a little water and solid ammonium carbonate added. On heating this solution under conditions and for a time calculated t o result in only a partial decomposition of t h e ammonium carbonate, t h e uranium and vanadium go into solution leaving t h e manganese, iron, a n d other impurities undissolved. T h e filtrate is acidified with sulfuric acid a n d boiled until i t is free from carbon dioxide, when a slight excess of carbonate-free ammonium hydroxide is added. This precipitates only the uranium and vanadium. I n common w;th other investigators we have not been successful in finding convenient and satisfactory procedures for separating these elements. The combined precipitates of uranium and vanadium are ignited at dull redness in a platinum crucible, allowing free access of air t o reoxidize any reduced material. The ignited residue is weighed as UsOs VzO6. I n general, only a small p a r t of t h e vanadium is present in this precipitate, t h u s malting it unavailable for t h e vanadium determination. I t is necessary, however, t o determine t h e vanadium t o correct t h e weight of uranium oxide. This may be done b y almost any of the several known methods for determining vanadium. T o this end we determine t h e vanadium after reduction with hydrochloric acid b y permanganate titration, and by oxidation with ammonium persulfate and silver nitrate, followed by electrometric titration. T h e latter method is t h e more certain and convenient, but t h e former gives entirely satisfactory results. For t h e purpose of either method t h e precipitate is dissolved in 50 cc. of concentrated hydrochloric acid and evaporated with 30 cc. of sulfuric acid (sp. gr. 1.58) until fumes appear. When
+
4
