ANALYTICAL CHEMISTRY
728 rases, the upper of the two bands is an orange color and thc?lower may be buff or yellow. T o avoid confusion, a mixture or 1111known should be developed until the bands actually separate. Variability of Adsorbent. The work reported herein wa- cioiic, with'a single lot of bentonite which had been in opni atoragt' in t.hc laboratory for approximately 4 years. No activation or drying \%-asnecessary for good results. A sample from cummt pi.oduction was obtained which also gave satisfactory results; however, it was necessary t o heat the material a t 110" in a vacuum oven for 6 hours before mixing x i t h the filter aid. A new T'olclay product, BC dust Volclay bentonite, also gave excellent separation but had a sloiver filtration rate than the 325-mesh T'olclay bentonite. The former should show greater uniformity from lot t o lot than the other product. The addition of more filter aid (to a 1 to 1 ratio) increased the flon- rate satisfactorily. Some indication was noted that th(' BC dust might require drying of tht, solvents for best results. Mixed Crystals. Brandstatter (I), in a study of mixed crystal formation with the 2,4-dinitrophenylhydrazones has stated that certain errors may be made in the estimation of their purity or identity. I n some eases the presence of a homologous impurity may raise the melting point of a dinitrophenylhydrazone. She also observed that certain mixed crystal systems may be mistaken for pure compounds. She found eight dinitrophenyl-,
hydrazones which shon ed thirteen complete series of niixed crystals. Of these thirteen pairs, six were studied by the author's procedure in this laboratory, and all were chromatographically separable. ACKXOW LEDGR.1ENT
The author is indebted to C. L. Ogg of the Analytical and Physical Chemistry Division for the nitrogen determinations. LITERATURE CITED
(1) Brandstktter, &I., Xikrochrmie w r . Mikrochim. Acta, 32, 33
(1944). ( 2 ) Brunner, H., and Farmer, E. H . , J . Chern. Soc., 1937, 1039. (3) Buchman, E. R., Schlatter, M .J.. and Reims, -1. O., J . Bm. C'hem. Soc., 64, 2701 (1942). (4) Drake, L. R., and Marvel, C . S., 1.O,,g. Chem., 2 , 387 (1938). (5) Johnston, C. D., Science, 106, 91 (1947). (6) Lucas, H. J., Prater, A. X., and Illorrij, R. E., J . Am. Chem. Soc., 57, 723 (1935). (7) Roberts, J. D., and Green, C . , IND. ENG.CHEM.,ANAL.ED.,18, 338 (1946). (8) Strain, H. H., J . Am. Chem. Soc., 57, 758 (1935).
RECEIVED January 15, 1948. I n giving the trade names mentioned in thin publication, the Bureau of Agricultural a n d Industrial Chemistry, United States Department of Agriculture, does not in a n y way guarantee thsee products nor are they reconimended in preference t o others not mentioned.
Accumulation of Traces of Arsenate by Goprecipitation with Magnesium Ammonium Phosphate I . 31. KOLTHOFF AND C. W. CARR, School of C h e m i s t r y , University of Minnesotu, .Minneapolis, M n n . A procedure is given for the quantitative coprecipitation of traces of arsenate with magnesium ammonium phosphate. In this way 0.075 mg. of arsenic dissolved in 500 nil. of solution can he determined with an accuracy of 2%. Metal ions that are precipitated in ammoniacal medium are made harmless b? the addition of an excess of tartrate. In the presence of much antimony a reprecipitation is necessary. The method can be applied to the determination of arsenic in steel that contains more than 0.01% of arsenic.
G
EKERALLY, coprecipitatiori is a great nuisance in quantitative gravimetric analysis. I n rare cases, however, it can be used t o advantage in the quantitative separation of trsres of constituents from solutionb and their separation from other suhstances. In order to accomplish this, a precipitate is produced in the solution which carries the microconstitiient down quantitatively. Quantitative coprecipitation can be expected Khen the microcompound forms mixed crystals x i t h the macroprecipitate, when the distribution coefficient is favorable, and when the proper conditions of precipitation are c h o s a . For example, lead sulfate forms mixed crystal3 x-ith barium and strontium sulfates. Traces of lead can he coprecipitated quantitatively, if a barium or strontium salt and then an excess of sulfate are added to the leadcontaining solution. The principle can also be used in the coprecipitation of traces of arsenate with magnesium ammonium phosphate. T h e salts M g X H 4 P 0 4 . 6 H 2 0and MgNH&04.6H20 are isomorphous (orthorhombic), and their axial ratios are almost identical ( 5 ) : MgNI11P04.6H20
a : b : c = 0.5667:1:0.9122 M ~ N H I A S O ~ . ~ H *aO : b : c = 0.5675:1:0.9122
Moreover, the solubilities of the two compounds are of the same order of magnitude. Use of the coprecipitation of traces of arsenate with magnesium ammonium phosphate has been made in the literature ( 1 , Z ) . However, there have been no systematic studies of the best conditions for quantitative coprecipitation of
arsenate and application of the method to the determination of small amounts of arsenic in the presence of other constituents in the solution. Such an investigation is described in t>hepresent paper. PROCEDURE .%NDANALYSIS
In gt:neral, a definite amount of monopotassium phvsphatr was added to the solution containing a known volume of arsenate solut,ion. After the solution had been made distinctly acid with hydrochloric acid an excess of magnesia mixture (50 grams of magnesium chloride hexahydrate and 100 grams of water) was added. (A slight excess of ammonia &-asadded and the solution allowed to stand overnight. If a precipitate was formed, the solution was filtered, slightly acidified with hydrochloric acid, and diluted t o 1 liter.) Concentrated aninionia was then added until the solution bccame just alkaline to methyl red. The concentration of reagents used was t,he same as given by Hillebrand and Lundell (9) in t,he procedure for the determination of phosphate. After most of the precipitate had formed, 5 ml. of ammonia were added in . The solution was alloaed to stand for 4 hours unless otherwise stated, and the precipitate n-as filtered and washed wit,h dilute ammonia (1 to 20).
As a great number of arsenate determinations had to be made, the simple procedure described by Kolthoff ( 4 )was used. The precipitate was dissolved in 20 ml. of 3 N hydrochloric acid and the arsenate reduced on the steam bath in a closed vessel after addition of 0.5 gram of pot,assiuni iodide. After being heated for 2 t o 3 minutes, the flask was cooled quickly, the liberated iodine was removed with sodium thiosulfate, the solution was care-
V O L U M E 20, N O . 8, A U G U S T 1 9 4 8
7 29
___
.~
.Jitabl(' i)!'oc?dUl 'fir11 oiily I raws of arsenic. have to be determined, a blank is i t h the phosphate solutioij tlrd iodine solution used i t ) and reagents and the amount of the blank is subtracted from that used i n the actual dcterminatioii. The iodine solution is standardized unditr the saint' ronditiona as prwail dui,iny the titration of tho unknown. 01'by all)-Uthf'r'
Table 1. Coprecipitation of i r s e i t i c Pentoxide with Phosphate (10 mi. of arsenate required 10 04 i i i l . of 0 . 0 1 .V iodiiir) PzOs, Grams per 100 111.of KHrPOa Solution 1 0.100 0.02: 0 . 0_ 1 .\ ~~___ _Iodine C.rd, 111. 10 0 5 10.04 8 3(i 10.04 10 00 8 78 10.08 10 0.5 8.25 _____~__ -
___
~~~
The pi.ncedurt~gavr. satisfar1 ory resulti eveii with v c y ~diluic, arsenic. solutions. As little as 0.075 mg. of arsenic. in ,500 nil. of solution cwuld he tleterniincd wit11 ~an accuracy of 2 7 (s'is determinations). In thic Table I!. Effect of 'I'inie of S t a n d i n g upon Coprecipitation case thr iodine \vas atantlardizorl b y taking 2 mi (10 1111. of 0 . 0 1 N .Idh i n 300 1111.: blank, 10 11 iiii. of 0 01 .\- Izr of 0.001 .V arsttnio tiiositl(, which was oxiclizcd nit11 I ' i i i i e o f standing a f t e r precipitation, i n i n . 0 ,j 30 60 120 240 broniino \vatel, and r c d u c 4 h y thcx yriwc.tlurt5 giveii. 0 0 1 .V iodine, in1. 8.6.5, 9 I O $4 .io, 9 7.5 9 . 3 . 7 ,9 . 6 0 Y.53, 1 0 . 0 0 10.09, 10 10 .A hlank deterniinatiori \vas riin to tlt~termim ~ ~ ~ ~ . _ _ _ the amount of 0.001 .\. iodine, added from B niicroburet, which was necessary to give H full!. ueutraliztd \\ 11 11 sidiuiii iiic.ai,iioiiatcL, and an ('xcesb ( i f tiicat,perceptible color change of the starch, This blank \vas subbonatc. was added. The araenic trioxide \\-as then titra Kith tracted from the anlounts of iodine used in tllc. stantlardizatiorl of an e s c standard 0.01 .V iodine solution i n thc ptwc~rict~ and in the actual titrations. carbonate, using starch solution as indicator. Blank txsp Determination of Small Amounts of Arsenic in the Presence of wit>h5- to 10-ml. portions of 0.01 .Y arwriatt, yivltltd thiwri.1 ic'al results within 0.3@;. Iron, Antimony, Tin, Aluminum, and Zinc. The precipitation of antimony, tin, aluminum, and iron in aninioniacal medium n-a+ COPHECIPITATION OF A H S k;S ATE U I T H J I A G N ESIUXI pitvented by the addition of tartaric acid. These mctalv in the AMMONIUiM PHOSPHATE I-,ighest state of oxidation form complvx c*onipoundawith tartrate Effect of Amount of Phosphate Used. Ten milliliters of 0.01 ,vhic.h I l o t prr,cipitatedt,.itb amrIionia, N arsenate were added t o 500 nil. of nionouotassium ohosuhatc ~* solution of varying strength; hence the original concentration of Procedure. To the solution containing 3 ml. of 0.01 ;V arscnatt. (1.9 mg. of arsenic) and 100 mg. of one of tht. above metals in the arsenate \vas only 0.0002 N . hftc,r prtxcipitatiori according to the form of its chloride, hromine rvater was a d d d until an ~ x c e s sw a ~ described, the results giver, in Table I ere prescnt. Two hundred milliliters of water, 1 gram of nioriopotaFAn amount of 500 nig. of phosphorus prntoxide per 500 nil. of siuln phosphate,, 3 gl'anis of tartaric acid, arid 25 1111.of magnesia solution t o be precipitated was sufficient t o give a quantitative niisturr n-ere added and then s l o d y 15 nil. of conc~r~ntrartd aninioiiia. After 2 hours of standing thtx precipitatr \VW f i l t ( . I ' c d and coprecipitation of tire arsenate. Therefore, this aniourlt of phosn.ashetl with dilute ammonia (1 to 20). Thc>arsenatv \vas deterphate was used in the following experiments. mined in the precipitate by the method described previously. In Effect of Time of Standing before Filtration of Precipitate. In t,he of antimony a reprecipitationn-as ncccssary, as sonle the general procedure the precipitate was allowcd to stand for 4 of the antimony was coprecipitated and interfered i n the determination of arsenate. After the precipitatr was dissolved in hyhours before filtration, 111 the c:xp,,,$ile1>ts reportcvJ in Table 11 drochloric acid, 0.5 gram of tartaric acid, 5 ml. of magnesia mixperiods of folthe precipit,ate ,ras filtered aft,sr ture, and ammonia were added, and filtration was niadc after 2 lowing addition of thrt excess of riiagnesia mixture. A4fter 30 hours of standirlg, .isevicieIlced from t h e &fa i n Tat,le ~ y , minutes of standing 96 to 9 7 7 ~of the arsenatt. \vas found in the rcwilts w r e obtained by t,he proc.cdurc~. precipitate. As the results depend somewfiat upon the exact The method v-as also used in the dt~terminatioii of awenic in manner of precipitation, which is hard t o reproduce, I\-aiting at samples of steel that contained more than 0.017; of arsenic. least 4 hours before filtration is rrcoinnit~nded. K i t h such unfavorable ratios of arsenic to iron a reprccipitation Effect of Shaking. Shaking t h e suspensions after additioIl oi is 11t'cessarY. the e x c c of ~ ~magnesia mixture pruniotcs precipitation of the arsenate, but the effect is not large enough to make shaking imperasample of steel containing at least 0. I nig. ( i f Pwcwum. tive in the general procedure. Thus, in the coprecipitation of the . arsenic is Tveigkledinto a 250-Inl, ~ ~flask anti dissolved l ~ in 25 ml. of 6 S nitric acid. In ordrr to enwre coniplrtv osidatioii arsenat,ein 500 ml. of 0.0001 S solution with 100 mg. of phosphoof arsenic to arsenate a few milliliters of broniinv wat(Jr are rus pentoxide the results given in Table 111were obtained. The SolUtion is boiled for a f P W IllinUtes and COOk'd. Ten E~~~~~of ~~~~~~i~ ~ i ~ d d ~~ d~h~ . tspeed of ~ precipita~ ~added. grams of tartaric acid for each gram of stcsel are added lx-ith 0.2 tion of arsenate increascs with iiirrcasing excess of magnesia mixof monopotassiurnphosphate and 50 nil, of magnt>sia niixture added. K h e n 500 ml. of 0.00008 S arsenate and 5 nil. of t,ure (tenfold escess). The solution transferred to a 250-nil. bottle, and concrntratrd ammonia i addrd until t h i w are at magnesia niixture tvere used-i.e., 2 1111. in escess-gOc7, !vas found l lvast 10 i d . in esrehi. Thr misturr is shakcn for 4 hours, ~ r l t the if the precipitate \vas filtered after 30 rrlinutes,y 5 ~ ; after 1 hour, and 99.,5% after 2 hours. K h e n 10 ml. of magnesia mixture -i.e., 7 ml. in excess--\\-ere used the figures were 08, 99, and 100% after 0.5, 1, and 2 hours of shaking. Thus, with an Table lll. Eflect of S h a k i n g ,,f Statlditlp amount of phosphate corresponding t o 300 mg. of phosphorus (Blank 5 04 i i i l . o f 0 0 1 5 iodine) pentoxide in 500 ml. the us(> of 10 nil. of inagnesia mixture is T h e of Standing 0 . 0 1 .\- Iodine, 311. recommended. niter Precipitation, ~~~
~
~
~~
~~
~
~
~~
11inu tes
Pilaken
~
~
~~~
S o t shakrn
Recommended Procedure. To the solution containing the at'30 4.55 4. 3 3 60 4.98 4 .8.i senic are added enough bromine water to give a yellow color (oxi5.04 4.53 120 dation of arsenic trioxide t o arsenate), an amount 340 5.03 .5 06 of phosphate corresponding t o 500 mg. of phos. phorus pentoxide per 500 ml. of solution, 1 ml. of hydrochloric acid, and 10 nil. of magnesia mixTable 1V. Deterniination of krsenic i n Presence of O t h e r I o n % ture. The solut,ion is neutralized with ammonia ( 1 . 9 rng. of arbenic. 100 ing. of other ions. Blank. 4 . 5 1 ml. of 0.01 .V iodiiit, and after most of the precipitate has been formed Elernent added Iron Tin Antiirionya hlurninuni Zinc 5 nil. of concentrated ammonia are added in excess. It is filtered after 2 to 4 hours standing, washed 0 . 0 1 S i o d i n e , rnl. 4.48, 4.4Y,4 . 5 1 4.49, 4.50, 4.52 4.48, 4 . 5 0 4,47. 4 . 4 9 4 48. 4 5 0 * Keprecipit,ation: after one precipitation 7 ,Os nil. of iodine were required. with dilute ammonia, and arsenate in the precipittLte is determined by the primdure mentioned ____
ANALYTICAL CHEMISTRY
730 precipitate is filtered off and dissolved in 3 S hydrochloric acid. One gram of tartaric acid, 10 ml. of magnesia mixture, and a n excess of ammonia are added to the solution. After shaking for 2 hours the precipitate is filtered and washed with dilute ammonia (1 to 20). The precipitate is dissolved in 3 S hydrochloric acid and the arsenat,e determined as described previously. When t.he amount of arsenic is small (of the order of 0.1 mg.) the titration is carried out with 0.005 iodine added from a microburet,. A blank is run following the same procedure, except that no steel is added. The amount of iodine required in the blank is subtracted from t,hat used in the det,ermination. The method was checked ivith a Bureau of Standards sample of ingot iron, 90.55, containing 0.012$, of arsenic. The results in cight determinations varied between 0.011 and 0.14Yc, n-ith a n average of 0.012%. K h e n the amount of arsenic in the steel \vas lcss than O . O l % ,
the blank was so large compared t o the amount of iodine used in the determination, that the resultswere not satisfactory. LITERMTURE CITED
(1) .Jssoc. Official d g r . Chem.. Official and Teiitative Methods of Analysis, 4th ed., p. 2 5 2 , 1935. ( 2 ) Beriitrop, Tudschrift 1'001'toeycpaste Scheikunde e n Hugiene, 4, 112
(1900-01).
IT.F., and Lundell, G. E. F., "Applied Inorganic Analysis," pp. 211, 509. Sew Tork, John Wiley &Sons, 1929. (4) Kolthoff, I. -M., "J-olunieti.ic Analysis," by N. H. Furman, Yol. 11,p. 410, New York. John Jl-iley Br Sons, 1929. ( 5 ) Mellor, J. IJ-,, "Coiiipreliensive Treatise on Inorganic and TheoVol. I V , p. 584, Val. IX, p. 177, London, Longmans, Green and Co., 1923. ( 3 ) Hillebraiid,
From a master's thesis submitted by C. \I-. Cam to the Graduate School, Uni\-ersity of Alinnesota, 1939.
RECEIVEDFebruary 5 , 1048.
Determination of Diphenyl Carbonate JEROME GOLDENSON AND SAMUEL SASS
Chemical Corps, Technical Command, Army Chemical Center, .Wd. Three analytical methods are described for estimating diphen11 carbonate in cloth: bromination of the phenol produced by alkaline decomposition, estimation of the blue indophenol color formed by the phenol decomposition product with 2,6-dibromoquinone chloroimide, and ultraviolet absorption nieasurements. A modification of the colorimetric indophenol method markedly stabilizes the color and is applicable to determinations of small amounts of phenol as well as diphenyl carbonate.
D
I P H E S l L carbonate, one of t h e new industrial chemicals available in commercial quantities, is being used for pharmaceutical manufacturing purposes. It has been found, by the U. S. Department of Agiiculture, Bureau of Entomology, Orlando, Fla., to be a promising miticide and larvacide, and is permitted for restricted use on the skin by the Division of Pharmacology of t h e Food and Drug Administration. I n connection with the study of miticides for impregnation in clothing being conducted a t the Army Chemical Center, it became necessary to devise methods of analysis foi this compound applicable t o clothing impregnated a ith the compound. h divcrsity of methods is desirable during development itages. The methods described in this paper involve broniinatiiig the phenol produced by alkaline decomposition of the compound; estimating the blue color formed by phenol 11 ith 2,6-dibromoquinone chloroimide by tpiansmittance measurements a t 565 to 630 millimicronq, using a photoelectric colorimeter; and measur ing ultiaviolet absorption. They x e r e found satisfactory for estimating various amounts of the compound in cloth and with niinoi changes may be of value in othei applications of diphen>l carbonate. APPARATUS
Soshlet typc extraction apparatus with standard-taper Erlenineyer flask. Beckiiian quartz spectrophotometer, AIodel CUV, range 220 to 1000 millimicrons, with interchangeable hydrogen discharge lamp in housing, and a pair of fused silica absorption cells with Pyrex covers. Nett-Summerson photoelectric colorimeter, 3lodel900-3, with brown color filter No. 59 with maximum transmittance a t 565 to G30 millimicrons, and calibrated test tubes. REAGEYTS A\D MMTERIALS
Cndyed pure-finish cotton herringbone twill, undyed, sized cutton herringbone tjvill, and olive drab cotton herringhone twill cloth.
Diphenyl carbonate, prepared by Chemical Division, Army Chemical Center, and recrystallized three times from ethanol, melting point 79 "-80' C. Reagents for Bromination Method. C.P. ethyl ether; potassium hydroxide solution approximately 0.2 IT; C.P. hydrochloric acid, concentrated; potassium bromate-potassium bromide solution of 3.5 grams of C.P. potassium bromate, and 13.0 grams of C.P. potassium bromide, made up to 1 liter with water; potassium iodide solution, 10%; sodium thiosulfate solution, 0.1 S ; and starch indicator solution, 1%. Reagents for Colorimetric Indophenol Method. Buffer solution of 28.4 grams of C.P. sodium tetraborate (?ITa2B107.10HnO1, and 5.9 grams of C.P. sodium hydroxide, made up to 1 liter with boiled and cooled distilled water ; 2,6-dibromoquinone chloroiniide (Eastman Kodak KO. 2304) solution prepared by dissolving 0.08 gram of the compound in 50 ml. of 95% ethanol and filtering into a dark brown bottle: and 0.3 S sodium hydroxide solution. The 2,6-dibromoquinone chloroimide solution should be kept in a cool, dark place and made up fresh a t least every second day. Thc buffer solution should be adjusted to a p H of 10 n i t h boric acid or sodium hydroxide, so that a solution of 0.20 ml. of thc buffer and 10 ml. of distilled water will have a p H of 9.8. DEVELOPMEVT OF METHODS
Ultraviolet Absorption Measurement. 9ome preliminary work vias done to make ultraviolet absorption measurements the basis of a n analytical method. The procedure applied was essentially the same as described by Gibb (-5) and KIotz (9). In order to obtain the optimum Xvave length, which is regarded as the wavc length of maximum absorption, the absorption spectra of diphenyl carbonate in concentrations of 0.01, 0.10, and 0.80mg. per nil. in 95Yc ethanol were determined. I t was indicated t h a t the most, pronounced absorption of diphenyl carbonate in 95c70 ethanol solution occurs in a wave band somewhere below 210 to 220 millimicrons, which is the lower limit of the Beckman quartz spectrophotometer used for this work. -knother lesser absorption peak for this compound occurs a t about 256 millimicrons, and it was found that concentrations of diphenyl carbonate in the range of 0.05 to 0.8 gram per liter of 95% ethanol may be estimated by
