T H E J O U R N A L OF I N D U S T R I A L A N D EiVGINEERING C H E M I S T R Y
578
.
Finally t h e lead bottoms are pounded into cubes t o remove any adhering particles of slag and are then weighed. The accuracy of t h e results were found t o depend upon the temperature a t which t h e fusions were made. The requirements are t h a t a high temperature should be used throughout, in order t h a t t h e required time may be short, so as t o minimize t h e reoxidation of t h e lead. According t o t h e equation 2Al 3PbO = AlzO; 3Pb, t h e weight of t h e lead multiplied b y t h e factor 0.0872 will give t h e equivaient weight of aluminum. The following results were obtained' on 3-8. samples of aluminum:
+
+
LSAD
-ALUMINUM--. Grams Per cent 2.9283 97.61 2.9489 98.29 2.9338 97.79 2.9195 97.32 2.9371 97.90 2.9271 97.57 2.9270 97.57
Grams 33.580 33.181 33.645 33.480 33.683 33.568 33.567
I t should be noted t h a t this method permits t h e use of a comparatively great weight of aluminum and further t h a t t h e fact t h a t t h e lead produced weighs nearly 1 2 times as much as the aluminum contributes t o t h e accuracy of t h e results. The method is quick, easy, and accurate from a practical standpoint. 111-DETERMINATION
O F NITRATES SALTS
IN
COMMERCIAL
At t h e present time t h e nitrates of potassium, barium, and strontium are extensively used in t h e manufacture ..of military pyrotechnics. A rapid and easy method for t h e determination of t h e pure nitrate content of t h e commercial salts depends upon the fact, t h a t when any of t h e above compounds are heated with an excess of tungstic anhydride (Woa), oxygen a n d oxides of nitrogen empirically corresponding t o N206 are liberated. Gooch and Kurzirian' have shown t h a t sodium paratungstate NaIcW12041 has t h e property of decomposing nitrates. It was found on trial, however, t h a t t h e use of tungstic anhydride gave better results owing t o t h e fact t h a t there was no loss b y spattering during t h e fusion, a loss difficult t o avoid if t h e paratungstate was used. One gram of t h e nitrate is mixed in a platinum crucible with approximately 5 g. of tungstic anhydride, prepared by igniting tungstic acid in a platinum crucible with a good Bunsen burner for an hour, and subsequently kept in a desiccator over sulfuric acid. The mixture is heated carefully over a Bunsen burner, finally using t h e full heat of t h e flame. The reaction is generally complete within I O min. From t h e loss in weight t h e percentage of t h e pure compound in the commercial sample is easily calculated. This method was tested with carefully purified samples of potassium nitrate, barium nitrate, and strontium nitrate, yielding results within 0.0j per cent of t h e theoretical in each case. 1
A m . J . Sci., [41 81 (1911), 497.
Vol.
12,
NO. 6.
THE APPLICATION OF THE ROTATING ZINC REDUCTOR IN THE DETERMINATION OF MOLYBDENUM By Walter Scott KENT CHEMICAL LABORATORY, YALE UNIVERSITY, NEWHAVEN,CT. Received January 5, 1920 INTRODUCTION
I n former articles' results have been given showing t h e efficiency and rapidity of rapidly rotating metallic reductors in t h e reduction and determination of vanadic acid and ferric sulfate. I n the present work a similar method has been applied t o molybdic acid. The reduction of molybdic acid b y zinc is well known. Wernke2 carried t h e reduction with zinc and sulfuric acid approximately t o t h e condition of MOIZO~Q. Using t h e Jones reductor, Dudley3 obtained slightly different results, while Jones4 and Doolittle and Eavenson6 obtained results similar t o those of Wernke. Blair and Whitfield,6 and Miller and Frank7 obtained a reduction approximately to t h e condition of Moq403,, while W. A. Noyes and Frohman,8 b y replacing a i r with carbon dioxide, got a degree of reduction corresponding t o MozO3. Randall,Qusing ferric alum in t h e reducing flask and decolorizing with phosphoric acid according t o Reinhardt'O obtained a reduction t o t h e condition of Moz03. REDUCTION O F
MOO3
B Y ROTATING ZINC CYLINDER
I n all t h e following results t h e molybdenum has been estimated as RiloO3, t h e source of molybdenum being ammonium molybdate1' which contained 81.35 p e r cent Mo 0 3 . Preliminary experiments showed t h a t t h e rate of reduction at temperatures between 20' and 30' C. was nearly as rapid as when started a t t h e boiling temperature of t h e solution, complete reduction being accomplished in about j min., for t h e amounts of M o o 3 taken. A t temperatures below 2 0 ° C., however, t h e reduction was much slower. I n t h e first series of experiments, t h e results of which are shown in Table I, t h e reduction was brought a b o u t b y a solid zinc cylinder into which was fixed an i r o n spindle attached t o t h e shaft of a small motor which was r u n by t h e ordinary city current. When an electrolytic current was used, i t was obtained from 8 storage cells. This cylinder was used in obtaining all 1 Gooch and Scott, A m . J . Sci., 46 (1918), 427; Scott, THIS JOURNAL, 1 1 (1919), 1135. 2 Z . anal. Chem., 1 4 (1875), 1 . 8 J . A m . Chem. Soc., 15 (1893), 519. 4 Am. Inst. M i n . Eng., 18 (1889-go), 705. 6 J . Am Chem. Soc., 16 (1894), 234. 6 I b z d . , 17 (1895), 747. 7 I b i d . , 26 (1903), 919. 8 I b i d . , 16 (1894). 553. 9 A m . J . Sci., [41 24 (19071, 313. 10 Chem.-Ztg., l a (1889), 323. 1 1 Treadwell-Hall (3rd Ed. (1911), p, 284) states that molybdenum trioxide may be obtained from ammonium molybdate b y heating carefully in a spacious crucible, finally t o dull redness. The writer found that a t very low redness a small amount of molybdenum trioxide always sublimed. This sublimation was overcome by thoroughly mixing the ammonium molybdate with 5 or 6 times its weight of acid tungstate of sodium, applying heat gently at first and finally t o low redness. The anhydrous acid tungstate .was prepared b y adding tungstic trioxide to fused sodium tungstate. The composition of the tungstate was practically NaaWzO7 or NaaO.2WOs.
June,
1920
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
the results which follow. A split cover-glass, in which a hole had been made slightly larger t h a n t h e iron spindle, was placed over the top of t h e tall, narrow beaker during every reduction. After reduction t h e solution was poured into a larger beaker and the volume made up t o about 350 cc. with ordinary distilled water (the solution changed from green t o amber) and titrated with standard permanganate. A correction factor of 0.09 cc. of the standard permanganate has been applied t o all t h e results recorded in this paper. This factor was determined under conditions exactly similar t o those of the experiments. TABLEI Total volume of solution reduced 53 cc Concentrated sulfuric acid, 5 cc (or better, 10 cc. 1 : 1 acid) Zinc surface in contact with solution, 70 sq. cm. Volume at Titration Cc. 350 350 350 350 350 350 350 350 350 350 350, 350 350 350 350 350 ~~
~
4-It seems advisable to allow the hydrogen in the solution t o collect in bubbles. These may be removed by slight jarring or by slowly moving a glass rod along t h e side and bottom of t h e beaker. 5-The permanganate is run into the beaker, and with careful stirring t h e reduced molybdenum solution need not come into contact with t h e air until about the Mo608 stage, when t h e oxidizing effect is negligible. Except where specified, t h e conditions of reduction are the same as in Table I. When reduction was started a t room temperature t h e solution warmed up 6' or S o ; when started a t t h e boiling point t h e temperature a t t h e end of t h e reduction was 70' t o So". TABLEI1
A-PRELIMINARY Time Temp. Temp. of before at Moo3 Reduc- Reduc- TitraMoOa Taken Found Error tion tion tion a C. O C. G. G. G. Min. 1 21 18 0.0818 0.0313 -0.0505 20 2 22 0.0818 0,0488 -0,0430 3 21 20 0.0818 0.0612 -0,0206 4 22 21 0.0818 0.0713 -0.0105 5 21 21 0.0818 0.0720 -0,0098 5 22 22 0.08181 0.0798 -0.0020 B-QUANTITATIVE Boiling 4 0.0818 0.0723 -0,0095 Boiling 4 0-.0818 0.0724 -0.0094 Boiling 4 0.0814 0 0702 -0.0 112 Boiling 4 0.0818 0:0709 -0,0109 22 5 0.0815 0.0705 -0.0110 22 5 0.0819 0.0704 -0.0115 22 5 0.0814 0.0704 -0.0110 22 5 0.0814 0.0716 -0,0098 22 5 0.0814 0.0705 -0.0109 22 5 0.0814 0.0697 -0,0117 1 Reduced and titrated in same beaker.
579
A-Reduction Rev. per Min. 700 700 700 700 700 700 700 700 700 700
These calculations are based on the assumption t h a t t h e MoOa is reduced t o MozOa. T h e low results indicate t h a t oxidation had taken place, yet t h e color showed t h a t t h e reduction was originally complete. T h e last experiment in (A) would seem t o indicate t h a t if t h e solution were titrated in t h e same beaker in which it was reduced quantitative results might be obtained. Later experiments proved this t o be true. QUANTITATIVE DETERMINATIONS
R E D C C T I O N A N D T I T R A T I O N I N S A M E BEAKER-In order t o obtain quantitative results, as recorded in Table 11, some care must be exercised t o prevent oxidation and undesirable reduction. I-The glass cover holds back enough hydrogen (from t h e action of sulfuric acid on zinc) t o form a protective covering during reduction. 2-When reduction is complete, as indicated by t h e appearance of a dark green color, t h e cover is removed, a n d t h e zinc cylinder (rotating slowly) is raised out of the solution and water sprayed on it. T h e rotary motion of t h e cylinder throws t h e water against t h e side of t h e beaker and it runs down on the surface of t h e reduced solution without causing any stirring or mixing. This water being lighter t h a n t h e reduced solution remains on t o p as a distinct layer, and forms a protective covering after reduction. 3-Small pieces of zinc are sometimes thrown off t h e cylinder and go into t h e solution. When this happens the solution should stand until t h e acid completely dissolves t h e zinc.
MOO3 Taken
G.
Started a t Boiling: Zinc Time of MOO3 ReducFound Error tion G. G. Min. 4.5 0.0808 -0.0010 4.5 0.0809 -0,0005 6.5 0.0809 -0.0010
0.0818 0.0814 0.0819 B-Reduction
Washed with Distilled Water Temp. Temp. Volume beat at Revolufore TitraTitrations tion per Reduc- tion * tion C. C. Min. Boiling 21 100 700 Boiling 21 100 700 Boiling 20 100 700
Started a t Boiling Temperature; Zinc Washed with Freshly Boiled Distilled Water 4 Boiling 50 100 700 0.0815 0.0807 -0.0008 4 .Boiling 55 100 700 0.0819 0.0813 -0.0006 C-Reduction Started a t Room Temperature; Zinc Washed with Distilled Water 6 20 27 100 700 0.0818 0.0810 -0.0008 5 21 28 100 700 0.0817 0.0817 -0,0010 5 22 28 100 700 0.0817 0.0805 -0.0012 5.5 20 28 100 700 0.0817 0.0810 -0.0007 D-Reduction Started at Room Temperature: Zinc Washed with Freshly Boiled Distilled Water 0.0817 0.0812 -0.0005 5.5 21 31 100 700 0.0816 0.0818 +0.0002 5 21 30 100 700 E-(Quantitative) Reduction. a t Room Temperature; Zinc Washed with Freshly Boiled Distilled Water 5.5 20 28 100 700 0,0816 0,0820 +0.0004 5.5 22 30 100 700 0.0818 0.0821 +0.0003 5.5 21 25 100 700 0.0818 0.0821 +0.0003 5.5 20 31 100 700 0.0819 0.0821 +0.0002 5.5 22 27 100 700 0.0816 0.0817 + O . O O O l
Table I1 shows t h a t t h e best results were obtained when reduction was started at room temperature and t h e cylinder washed with distilled water which had been freshly boiled. R E D U C T I O N BY R O T A T I N G Z I N C ANODE-The results in Table I11 were obtained by making t h e zinc cylinder t h e rotating anode and a piece of platinum 5 b y I O cm. t h e stationary cathode. Otherwise t h e conditions were t h e same as in Table 11-E. TABLEI11 A-PRELIXINARY MOO, Taken
MOO3 Found
Error
G.
G.
G.
0.0814 0.0814 0.0814 0.0814
0.0516 0.0670 0.0775 0.0512
-0,0298 -0.0144 -0.0039 -0.0002
0.0815 0.0815 0.0816 0.0814
0.0813 0,0811 0.0814 0.0811
-0.0002 -0.0004 -0.0002 -0.0003
Time TemD. Vol. of befope at Reduc- Reduc- Titration tion tion Min. O C. Cc. 1 22 150 2 22 150 3 22 150 4 22 150 B-QUANTITATIVE 4.5 22 150 4.5 21 150 4.5 23 150 4.5 21 150
Rev. per Min. 700 700 700 700
Current Used Amp. 6 6 6 6
700 700 700 700
6 6 6 6
These \results show t h a t t h e reduction, when t h e electrolytic current was used, was brought about in a little less time t h a n when no electrolytic current was used. D E T E R M I X A T I O N O F M O L Y B D E N U M USING I R O N S O L U -
TIoN-The
results in Table I V were obtained b y
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
580
reducing the molybdenum by the rotating zinc cylinder (no electrolytic current) and then pouring the reduced solution into a beaker containing ferric alum and phosphoric acid (2 j cc. ferric alum solution, made by dissolving IOO g. ferric alum in I liter ot water; j cc. sirupy phosphoric acid). TABLEI V MOO8 Taken
G.
0.0815 0.0818 0.0816 0.0819 0.0816 0.0815 0.0814
Moos
Found by KMn04 0.0818 0.0818 0.0811 0.0812 0.0814 0.0815 0.0810
Error G. 4-0.0003 0.0000 -0.0005 -0.0007 -0.0002 0.0000 -0.0004
Time of Temp. Vol. at Reduc- before Titrstion Reduction tion Min. O C. cc. 5.5 5.5 5.5 5.5 5.5 5.5
5.5
25 30 23 22 22 21 22
400 400 400 400 400 400 400
Rev. per Min. 700 700 700 700 700
700 ,700
The above results show t h a t the reduced molybdenum solution may be titrated in a separate beaker from t h a t in which i t was reduced, provided the mixture of ferric alum and sirupy phosphoric acid is used to effect t h e preliminary oxidation of the molybdenum while in the very sensitive stage.
Vol.
12,
No. 6
desired. A situation arose a t this plant not long a g o demanding t h a t the arsenic content of each shipment of acid be determined before the shipment was received. The literature on this subject was accordingly examined, and various methods tried, but all proved: laborious and time-consuming. Some of t h e methods involved the reduction of t h e arsenic in the arsenic form, some a precipitation with hydrogen sulfide, and some both of these procedures. T h e ones giving t h e best results were t h e most time-consuming, t h e operation requiring t h e greatest amount of time being t h e reduction of the arsenic form. I t was thought, accordingly, t h a t a method involving t h e determination of e&ch form of arsenic separately would be very advantageous. The determination of arsenious arsenic presented no particular difficulty, as a slight modification of one of the standard methods would suffice. T h e method for the determination of each form finally adopted is given below.
CONCLUSIONS
The foregoing results show t h a t molybdic acid in dilute sulfuric acid solution may be reduced by a rotating zinc cylinder, either with or without the aid of the electrolytic current, when certain precautions have been observed; also t h a t when ferric alum a n d sirupy phosphoric acid are added immediately t o t h e reduced molybdenum solution, t h e titration may be made in a separate beaker from t h a t in which reduction is brought about. The molybdic acid may be determined quantitatively in all cases by titrating the reduced solution with standard potassium permanganate. The above processes may be advantageously used in place of the ordinary Jones reductor, after interfering substances have been previously removed by any of t h e ordinary methods. Assuming ammonium phosphomolybdate t o have the composition ("4)sP04.12Mo03, P or PzOs may be indirectly determined by this method. I t might also be added t h a t when t h e work on this series of articles terminated, t h e writer was working on a volumetric method for the determination of tungsten (or tungsten trioxide) and had succeeded in keeping it completely in solution practically t o t h e W 0 2 stage. This process will be further investigated a t some future time. ACKNOWLEDGMENT
This work was done in the Kent Chemical Laboratory of Yale University in 1916, and the writer wishes t o thank Professor F. A. Gooch, whose interest was stimulating and kindly advice most helpful a t all times. A RAPID METHOD FOR QUANTITATIVE DETERMINATION OF ARSENIC IN COMMERCIAL SULFURIC ACID By A. A. Kohr SEABOARD BY-PRODUCT COKECo.,JERST~Y CITY,N. J. Received January 29, 1920
I n various commercial operations where sulfuric acid is used, an acid of low arsenic content is often
METHOD
A R S E N I O U S FORM-weigh o u t 2 0 g. of acid and dilute with a small amount of distilled water, and add a f e w drops of methyl orange indicator. Carefully neutralize with a saturated solution of sodium carbonate until t h e methyl orange shows a very faint pink (about o n e drop more would t u r n the solution completely yellow), and add about 2 g. of sodium *bicarbonate powder in excess. Make up solution t o about 2 5 0 cc. with distilled water, if necessary, and titrate with 0.1 N iodine solution, using starch as a n indicator. A blank determination should be made on the reagents and suitable correction made. Cc. 0.1 N iodine X 0.004gj = g. As203 in t h e arsenious form. ARSENIC FORM-weigh out 2 0 g. of the acid t o b e tested into a small beaker, and place in a n oven regulated a t ~ o j 't o 110' C. for about a n hour. Dilute with a small amount of distilled water, and add a. saturated solution of sodium carbonate until just in excess (red color with phenolphthalein). Boil, and: filter into an Erlenmeyer flask. Wash thoroughly a n d add about 3 g. sodium bicarbonate powder, add 1 5 0 cc. strong hydrochloric acid slowly with occasional agitation, then add about I g. potassium iodide crystals, and cover the flask t o keep out air. Agitate and then allow t o stand j min. Titrate the iodine liberated with 0.1N thiosulfate, with starch as indicator. Cc. 0.1 N thiosulfate X 0.004gj = g. As203 i n arsenic form. arsenic in arsenious. Arsenic in arsenic form form = total Asi03. Total As20s X j = per cent total AszOa. Per cent total AszOs x 0.757 j = per cent total As.
+
DISCUSSION
+ +
+
H ~ A s O ~ 2HI HaAsOs I2 HzO The above reaction proceeds from left t o right whern t h e hydrogen-ion concentration is low, and there.
