I is
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
Vol.
11,
No.
2
\
APPARATUSF O R MANURACTURE OR ARSENIC TRICHLORIDE
trace of arsenic trioxide. If opened when too hot, t h e sulfur residue is liable t o take fire. T h e charge of arsenic trioxide was divided into two parts in order t o use agitation during as much of t h e process as possible. T h e first charge required about 1 1 / ~ hrs. t o complete and t h e second charge about 3 hrs. T h e total time of operation was between 71,12 and 8 hrs. Based on t h e amount of sulfur chloride used t h e yield was 93 per cent of product averaging 9 9 per cent pure.
T h e first dist,illate which was always colored was decolorized b y redistilling with a small amount of arsenic trioxide. This investigation was started under t h e Bureau of Mines a t t h e American University Experiment Station a n d was continued under t h e Research Division of t h e Chemical Warfare Service. SMALL SCALE MANUFACTURING SECTION RESEARCH D I V I S I O N , c. TV. s., U. s.A .
’
E X P E R I ~ E N T STATroN
AMERICAN
WASHINGTON, D. C.
IGINAL PAPERS THE DETERMINATION OF CADMIUM BY THE HYDROGEN SULFIDE METHOD By EDWARD SCHRAMM Received August 12, 1918
1-1
NTR 0 D U C TI 0 N
I n t h e Course of some cooperative work on t h e determination of small quantities of cadmium in brass i t was found t h a t varying results were obtained b y several laboratories. A diversity of methods is in current use, most of which do not appear t o have been tried out on materials of known composition.l T h e present work was accordingly undertaken with a view t o developing a convenient and reliable procedure for this determination, and t o ascertaining what degree of 1 TWOmethods have been described in considerable detail in t h e second edition of Price and Meade, “Technical Analysis of Brass,” p p , 229-233.
accuracy is t o be expected. T o accomplish these aims, analyses were made of brasses with cadmium additions and of salt mixtures of known composition. T h e hydrogen sulfide precipitation was chiefly employed for t h e necessary separations, and accordingly t h e work became primarily a s t u d y of t h e most suitable conditions for separating a small amount of cadmium from other metals b y this method. Structural brasses may contain, besides t h e principal constituents, copper and zinc, one per cent or more of ‘tin, and varying quantities of lead, iron, manganese, arsenic, and other metals, which may have been added intentionally or introduced accidentally as impurities in the copper or zinc. Very little has been published on t h e determination of cadmium in brass, b u t its determination in spelter has been t h e subject of a
Feb., 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 ENGINEERIYG C H E M I S T R Y
considerable amount of work, part of which will be briefly reviewed. 11-REVIEW
O F LITERATURE
H. J . S. Sand’ studied t h e electro-analytical separation of t h e metals b y t h e graded potential method. T h e separation of cadmium from zinc was performed in acetate solutions containing free acetic acid. J. J. Fox2 separated cadmium from zinc as sulfide i n t h e presence of trichloracetic acid. This method is said t o obviate t h e difficulty experienced in determining t h e proper concentration of mineral acid necessary for t h e complete precipitation of cadmium sulfide, uncontaminated with zinc sulfide, and t o abolish t h e m a n y solutions and reprecipitations necessary t o purify t h e cadmium sulfide. W. D. Treadwell and H. S. Guiterman3 found t h a t t h e hydrogen sulfide separation gave bettkr results in sulfuric t h a n in hydrochloric acid solutions, less zinc being carried down. They recommended t h a t t h e solution should be 4-5 N in sulfuric acid, a n d t h a t hydrogen sulfide should be passed into t h e hot solution until i t is cold. Treadwell and Guiterman also carried out t h e separation electrolytically, using oxalate o r sulfate solutions; with t h e latter they found t h a t 0.04 t o 0 . 2 g. of cadmium could be separated from fifty times t h e amount of zinc. E . J . Ericson4 separated cadmium from zinc b y successive hydrogen sulfide precipitations in sulfuric and trichloracetic acid solutions. The same author has described a separation of zinc from cadmium depending on t h e crystallization of zinc sulfate.5 W. Cooper0 dissolved j g. of zinc in dilute sulfuric acid and passed hydrogen sulfide into t h e cold solution. T h e precipitate was filtered off a n d dissolved in hydrochloric. acid and bromine water, sulfuric acid was added, and t h e solution evaporated t o t h e appearance of fumes. After filtering out a n y lead sulfate t h e process was repeated twice, and the cadmium was finally weighrid as sulfide after drying a t I O O O . A procedure commonly used in this country is t h e s t a n d a r d method of t h e American Society for Testing Materials.’ This consists briefly in dissolving 2 j g. of drillings in dilute hydrochloric acid until nearly all t h e zinc has been dissolved. T h e residue, presumed t o contain all t h e cadmium, is dissolved in nitric acid and evaporated with sulfuric acid t o t h e appearance of fumes t o remove t h e lead. T h e filtrate is diluted t o 400 cc , I O g. of ammonium chloride added, and hydrogen sulfide is passed in. I t is occasionally necessary t o s t a r t t h e precipitation of t h e cadmium sulfide b y t h e addition of a drop or two of ammonia. T h e impure cadmium sulfide is filtered out b y means of a Gooch crucible and is dissolved by boiling for hr. with I : j sulfuric acid. The solution is filtered, diluted t o 300 cc., and t h e cadmium sulfide reprecipitated. This may be repeated a third time. T h e cad1
2
3 4
6 6
7
J Chem S O C ,91-2, 373-410; 93-4, 1572-92. I b z d , 9 1 (1907), 964-7. Z anal Chem , 52, 459-70. L?zI:Mzn J , 8 7 , 1036 THISJ O U R N A L , 9 (1917), 670. Chem X e w s 110 11914), 250-1. THTS JOURNAL, 7 (1915), 547.
111
mium sulfide is dissolved in hot dilute hydrochloric acid ( I : 3), and finally converted t o sulfate and weighed as such. 111-GENERAL
CONSIDERATIONS
Obviously none of t h e methods above outlined can be adopted as such for t h e determination of cadmium in brass because of t h e tin and t h e large amount of copper present. After t h e removal of these elements, a n y of t h e methods and especially t h e last, with certain modifications, may be taken as a guide t o t h e further separation. T h e precipitation of t h e copper and cadmium together as sulfides followed by extraction with boiling dilute sulfuric acid has been employed b y some analysts, b u t seemed a clumsy operation because of t h e great quantity of copper present. T h e best procedure therefore appeared t o be t h e electrolytic separation of t h e copper from nitric acid solution, preceded b y removal of t h e tin as metastannic acid. It is better t o remove tin t h a n lead a t t h e s t a r t since t h e former is much more likely t o contaminate t h e cadmium in subsequent operations. After t h e removal of t h e copper, t h e standard method of the American Society for Testing Materials was applied with certain changes in detail, and with t h e additional precaution of treating t h e cadmium sulfide with ammonium polysulfide before t h e final conversion t o sulfate. A brief consideration of t h e vital steps in t h e process outlined will assist in determining whether i t will accomplish t h e desired separations, and in fixing suitable details. We should not expect a n y deposition of cadmium during the electrolytic separation of t h e copper. With t h e very small concentrations of cadmium in question, a high potential would be required for its deposition under t h e most favorable conditions. It is well known t h a t the concentration of nitric acid here employed (about 3 per cent) will prevent the separation of cadmium even from strong solutions. As a n added precaution, t h e electrolysis should never be carried on long enough t o cause much reduction of nitric acid, and should be stopped before all t h e copper is deposited. The second vital step in t h e method is t h e precipitation of cadmium with hydrogen sulfide and its separation from zinc. I n a solution of hydrogen sulfide1 we have t h e following relation between t h e ions:
[Hfl2 X [ S = ]
=
Kz =
1.1
x
10-~3
The concentration of t h e sulfide ion is inversely proportional t o t h e square of t h e concentration of t h e hydrogen ion. Now for t h e precipitation of cadmium sulfide t o occur we must have [Cd++l X Is=]> Keds, where KCds represents t h e solubility product constant of cadmium sulfide. Obviously, t h e larger t h e value of S= (hence t h e smaller t h e value of HT), t h e smaller will be t h e concentration of Cd++ remaining in solution in equilibrium with t h e precipitated gulfide. If, however, t h e value of S= is made too large, t h e solubility product of zinc sulfide will be exceeded and we 1
Stieglitz, “Qualitative Analysis,” 1, 199, et seq.
I12
THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
shall fail t o effect a separation. We therefore seek t o regulate the acidity so as t o permit cadmium b u t not zinc t o come down. I n t h e standard method for spelter (starting with a 2 j g. sample) this is done b y dilution t o 300 or 400 cc. Now i n diluting in this way, while we increase S= we a t t h e same time decrease Cdf’. It would therefore appear better t o keep t h e solution as concentrated as possible in cadmium and regulate t h e acidity b y other means t h a n dilution. Moreover, since for a given hydrogen-ion concentration t h e concentration of cadmium in solution is fixed, t h e more dilute the solution t h e more cadmium will escape precipitation. T o p u t t h e same proposition in another way-if we start with a I O g. sample and precipitate in a volume of I O O cc., t h e percentage loss will be no greater t h a n starting with 40 g. and precipitating in a volume of 400 cc:, provided t h e acidity is t h e same in both cases. By using a smaller sample, therefore, we should lose nothing i n t h e ability t o separate cadmium, avoid t h e trouble of r e m o v h g t h e large amount of copper, a n d greatly simplify manipulations. With a I O g. sample 0.01: per cent cadmium will give 0.0019 g. of cadmium sulfate which can be weighed with suficient accuracy. T h e third important question concerns t h e freedom from contamination of t h e cadmium sulfide, and t h e means taken t o purify $t, The repeated precipitations in regulated acid solution insure complete separation from zinc, iron, and manganese, while t h e boiling with dilute sulfuric acid accomplishes separation from small amounts of copper and lead not removed during electrolysis. Finally, t h e treatment with ammonium polysulfide removes a n y sulfides of tin, arsenic, or antimony which would not have much effect on t h e color of t h e precipitate. (This precaution appears in most cases unnecessary, since these elements can be separated in previous operations. If, however, a great amount of tin were originally present i t is safer t o adopt it.) It is considered b y some t h a t t h e alkaline sulfide treatment results in loss of cadmium, b u t Noyesl has shown in his “System of Qualitative Analysis” t h a t i t is possible t o t r e a t 500 mg. of cadmium sulfide with ammonium polysulfide and not find any cadmium in the filtrate. Rowever, i t must be recognized t h a t cadmium sulfide has a tendency t o go through t h e filter in t h e colloidal condition, b u t this can be avoided by adding ammonium chloride, as recommended b y Noyes, and in carrying out t h e final precipitation in small volume. Under these conditions t h e cadmium sulfide does not go into t h e colloidal condition and can safely be treated with ammonium polysulfide. IV-EXPERIMENTAL
RESULTS
The first method used, based on t h e principles discussed above, was as follows: Dissolve I O g. of brass in 75 cc. of nitric acid (I : I ) and boil for 30 min. Filter off the metastannic acid, dilute to 350 cc., add I O cc. of sulfuric acid (I:I), and electrolyze till nearly all the copper is removed and the lead deposited on the anode as peroxide. The solution is then treated as in the standard method for spelter, except that precipitations are made in smaller volume, and that a final treatment with ammonium polysulfide is employed. 1
Technoloey Quarterly, 19, 274. \
Vol.
11,
No. z
T o test t h e method, analyses were made of several brasses with and without additions of cadmium. T h e results are given in Table I. TABLE I Cadmium Added Per cent 0.0 0.016 0.0 0.020
SAMPLE
No. 1 2
................. .................
Cadmium Found Per cent 0.007 0.025 0.034 0.049
Added Cadmium Recovered Per cent 0.018
0.015
Determinations of cadmium on I O samples of manganese bronze were carried out, t h e results ranging from o t o 0.034 per cent. On several of these, duplicates were r u n and good checks obtained. Some time after t h e experiments just described had been completed, t h e matter of cadmium determinations again came up, and t h e work was resumed i n a n effort, if possible, t o simplify t h e manipulations. M y attention was called t o t h e complication caused b y t h e presence of arsenic. I n working on a sample containing 0.1j per cent arsenic and low in cadmium t h e original method was modified in several respects. I n t h e first precipitation with hydrogen sulfide, ammonia was added till zinc began t o come down. Only one treatment with I : 5 sulfuric acid was employed. T h e second precipitate of sulfides (containing much of t h e arsenic) was extracted with cold dilute hydrochloric acid ( I : I ) , t h e arsenic sulfides remaining unattacked. After a third precipitation with hydrogen sulfide, t h e solution was evaporated t o dryness with suifuric acid and t h e first weighing of cadmium sulfate made directly. As a check in some cases t h e cadmium was again taken into solution, reprecipitated as sulfide, and t h e latter purified as before. T o test this modified procedure a mixture of salts was made up containing 6 g. of copper, 3.j g. of zinc, and 0.1g. each of tin, manganese, iron, lead, and arsenic. This mixture was run as a blank and with graded additions of cadmium. T h e results of these experiments are given in Table I1 and some analyses of brasses in Table 111. TABLE11-ANAZYSES OF SALTMIXTURESCONTAINING Cu, Zn, P b , Fe, Mn, As, AND Sn Cadmium Found Per cent
Cadmium Added Per cent 0.00
...
0,008 0.013 0.015 0.019 0.024 0.030 0.035
0.01 0.01 0.02 0.02 0.03 0.03 0.04
------Difference-
Per cent
Actual
...
-0,002
i-0.003 -0.005 -0.001 -0.006 0.000
-0.005
Mean 0 000
0.000
-0.003 -0.003
-0.005
TABLE111-ANALYSES OF BRASSES Cadmium Found Per crnl
MATERIAL Arsenical Brass.
........................
................................. ............................... Brass C . . ............................... Brass D . ................................ Brass A
Brass B . .
0.013 0.013 0.014 0.054
0.057 0.020 0.019 0.027 0.022 0.021 0.022
T h e results in Table I1 on salt mixtures show t h a t t h e values obtained are wi%hin 0.005 per cent of t h e true cadmium content and t h a t they tend t o be slightly
Feb., 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
low rather t h a n t o o high. This is what one would naturally expect, since there are a number of precipitations a n d filtrations, with opportunity in each operation f o r a slight loss of cadmium, b y solution as well as b y mechanical loss. Brasses can be r u n with a t least t h e same degree of accuracy, since t h e salt mixtures used contained a greater proportion of possible interfering substances t h a t is likely t o be met with in a n ordinary brass. Table I11 shows t h a t excellent agreement can b e obtained. As a final check, a n d t o guard against t h e possibility of t h e results obtained being d u e t o a balancing of errors, t h e cadmium sulfate residues from t h e salt mixtures, as well as from t h e brasses, were carefully examined. T h e y were pure white a n d completely soluble in water. T h e combined solutions failed t o give a n y test for interfering substances which could conceivably have been present. T h e procedure for determination of cadmium in brass as finally adopted is as follows: Dissolve IO g. in 75 cc. of nitric acid (I : I). Boil the solution ‘/z hr. and filter off metastannic acid. Dilute to 350 cc. which should bring the concentration of nitric acid to about 3 per cent. Add I O cc. of sulfuric acid (I:I) and electrolyze with a current of 4 amp., using rotating anode, until the copper is nearly all removed, which should take about zl/z hrs. Siphon off the electrolyte, add another IO cc. of sulfuric acid, and evaporate over night nearly to dryness. Dissolve in IOO cc. of water, neutralize with ammonia, add 5 cc. of I : I sulfuric acid, pass hydrogen sulfide into the cold solution 30 min. until the sulfides settle. Add ammonia until zinc begins to come down and pass in hydrogen sulfide 30 min. more. Filter, using water containing ammonium chloride and hydrogen sulfide to wash the precipitate out of the beaker. Boil the precipitate 15 min. with 20 cc. of I :5 sulfuric acid, maintaining the volume by adding water occasionally. Filter and wash, keeping the volume down to 50 cc. Add 5 cc. of strong ammonium hydroxide, pass in hydrogen sulfide 112 hr., adding ammonia until the cadmium begins to come down. Filter and treat the precipitate with a little cold hydrochloric acid (I :I). Neutralize the solution with ammonia and add 5 cc. of I :5 sulfuric acid, keeping the volume down to about 30 cc. Pass in hydrogen sulfide as before and add ammonia to start the precipitation of the cadmium, Filter, dissolve the cadmium sulfide on the filter in a little I :I hydrochloric acid. Collect the solution in a weighed platinum or porcelain dish, add I cc. of sulfuric acid, evaporate to fumes, and add a little concentrated nitric acid. Evaporate carefully to dryness and finally weigh as sulfate. If there is any possibility of the presence of tin, dissolve the cadmium sulfate in 2 5 cc. of water and 5 cc. of I :5 sulfuric acid and reprecipitate with hydrogen sulfide, adding a little ammonium chloride to the solution. Let the sulfide settle, decant through a filter, add a little ammonium polysulfide and ammonium chloride to the precipitate in the beaker, warm for several minutes, and pour through the filter. If there is any turbidity, refilter until the solution comes through clear. Finally dissolve the cadmium sulfide in hydrochloric acid and proceed as before with the evaporation and weighing. In conclusion, it will b e well t o call attention t o cert a i n possible sources of error a n d i m p o r t a n t precautions to b e observed, Because of t h e mass of salts present, t h e first precipitation with hydrogen sulfide must b e made i n a somewhat larger volume t h a n t h e later precipitations, i. e., under less favorable conditions. T w o means are t a k e n t o counteract this. A small p a r t of t h e copper is allowed t o remain in solu-
I I3
tion after electrolyzing a n d t h e copper sulfide precipitated tends t o a c t as a carrier a n d bring down t h e cadmium. I n addition t h e acidity is reduced so a s t o permit t h e precipitation of p a r t of t h e zinc, under which condition t h e solubility of cadmium sulfide is greatly lowered. I n later preFipitations t h e volume of solution is so small t h a t t h e cadmium sulfide forms readily, a n d t h e acidity can be so regulated as t o effect a separation from zinc without a n y great proportion of t h e cadmium remaining in solution. I t may sometimes happen, however, if t h e concentration of hydrogen ion is too small, t h a t some zinc will come down with t h e third precipitate of cadmium sulfide. This can usually be detected b y t h e color of t h e precipitate or b y t h e appearance of t h e cadmium sulfate residue, a n d when it occurs a fourth precipitation must be made. Finally, it must be remembered t h a t cadmium sulfide is insoluble in a solution containing z or 3 per cent sulfuric acid only when t h e solution is saturated with hydrogen sulfide. Such solutions, however, are unstable a n d if allowed t o s t a n d i n a n open beaker, gradually lose their hydrogen sulfide. As a result of t h e removal of t h e sulfide ion t h e solubility product of cadmium sulfide is no longer exceeded, t h e reaction is reversed, a n d finally all of t h e cadmium goes back into solution. On t h e other hand, if insufficient time is allowed, t h e cadmium sulfide remains in a colloidal condition a n d runs through t h e filter. As pointed o u t above, t h e presence of ammonium salts t e n d s t o coagulate t h e sulfide, which can be successfully filtered under t h e conditions described. If a n y runs through, a second filtration will suffice t o retain it. I n case i t is desired t o allow t h e precipitate t o stand, t h e solution must be placed in a tightly stoppered vessel or i n communication with a hydrogen sulfide reservoir so t h a t equilibrium m a y be established between t h e solution a n d a definite pressure of t h e gas. It is doubtless through neglect t o consider one or several of t h e conditions dwelt on i n this paper t h a t low results f o r cadmium have been sometimes reported. RESEARCH DEPARTMENT AMERICAN ZINC,LEADAND SMELTING COMPANY a b ST. LOUIS,MISSOURI
THE DETERMINATION OF PHOSPHORUS IN VANADIUM STEELS, FERROVANADIUM, NON-VANADIUM STEELS, AND PIG IRON B y CHAS. MORRISJOHNSON Received July 12, 1918
I-METHOD
FOR
S T E E L CONTAINING 2.6 P E R C E N T
VANADIUU UP
TO
Ibbotson a n d Brearley, i n 1902,~ recommended t h a t phosphorus be precipitated from t h e reduced solution of vanadium, using ferrous sulfate as a reducing agent, claiming thereby t o aid in t h e precipitation of phosphorus when vanadium is present. Cain a n d Tucker, i n 1g13,2 recommended t h a t t h e vanadium present be reduced with ferrous sulfate a n d sulfurous acid for t h e same purpose. 1 2
“Analysis of Steel Works Materials.” THISJOURNAL, 5 (1913), 647.
