V O L U M E 2 4 , NO. 1 2 , D E C E M B E R 1 9 5 2 could be readily applied to the toxicological estimation of carbon monoxide in air (4)and in blood ( 6 ) . ACKNOWLEDGMENT
This Jvork was supported by a grant from the Division of Research Grants and Felloiyships of the Sational Institutes of Health, C. S. Public Health Service. LITERATURE CITED
(1) Ayres, G. H., ANAL.CHEM.,21, 652 (1949). (2) Ayres, G. H., and Tuffly, B. L., Ibid., 24, 949 (1952).
1997 (3) Brady, 0. L., and Goldstein, R. F., J . Chem. Soc. (London), 1927,
1960. (4) Christman, A. A , , Block, W. D., and Schults, J., IND.ENG. CHEX,ANAL.ED.,9, 153 (1937). ( 5 ) Christman, A. A., and Randall, E. L., J . Biol. Chem., 102, 595 (1933). (6) Hayes, J. R., and Chandlee, G. C., 1x0. ENG.CHEDI.,AXIL. ED., 14,491 (1942). (7) Roe, J. H., and Rice, E. W., J . Biol. Chem., 173, 507 (1948). (8) Syrokomskii, V. S., and Gubel'bank, S. RI., Zhur. Anal. Khim., 4, 203 (1949). RECEIVED for r e i i e w June 30, 1952. Accepted July 28, 1952.
Estimation of Sodium Triphosphate Improvement in Zinc Titration Method RUSSELL N. BELL, A. R. WREATH, AND WILLIAM T. CURLESS Research Laboratories, Victor Chemical Works, Chicago Heights, 111.
hCE the publication of the Bell method ( 1 ) the commercial sliroduction of sodium triphosphate has increased tremendously and with i t the quality of the product. Formerly the commercial material often contained only 75 to 85% sodium triphosphate, the remainder consisting largely of tetrasodium pyrophosphate with occasional small percentages of ortho- and metaphosphatc,s. Improvements in production methods have led to commercial products which now usually assay over 90% sodium triphosphate. Because of these recent advances, a more highly refined method for the estimation of sodium triphosphate became desirable. The Bell method for the estimation of triphosphoric and pyrophosphoric acids in the presence of ortho- and metaphosphoric acids consists of the following steps: 1. Titration of the sulfuric acid liberated when a solution of zinc sulfate is added to a solution of the mixture adjusted to p H 3.8. 2. Gravimetric determination of the pyrophosphate precipitated as the zinc salt. Excess of liberated acid over that required by the pyrophosphate is calculated as triphosphate using an empirical factor.
+ 2Zn++ +Zn2P207.1 + 2 H HnPaOlo--- + Zn+- F-* ZnPBOlo--- + 2" H2P?07--
The present work was undertaken to determine the effect of certain variables on the method in an effort to increase the accuracy when applied to present-day commercial sodium triphosphate. PREPARATlON OF PHOSPHATES
Tetrasodium Pyrophosphate. The sodium pyrophosphate (SaaP,Or) was recrystallized commercial material dried a t 400 C. Sodium Triphosphate Hexahydrate. The sodium triphosphate (NasP8010. 6 H 2 0 ) was prepared from commercial anhydrous sodium triphosphate by t\To methods. 1. A 14% aqueous solution of sodium triphosphate was prepared and filtered. Alcohol was added to the filtrate until the first permanent precipitate appeared. The slurry was allowed to stand until all of the triphosphate had precipitated. The crystalline product was filtered and washed first with 50% alcohol, then with 95% alcohol, after which it xvas air-dried. Table I.
Analysis of Phosphates KasPsOlo
~
NarPzOi Calcd., Found,
7 PoOa % Loss'on ignition,
9%
53.4 0.0
0
Caicd.,
%
%
53.4 0,O
44.7 22.7
F o u n d , 70 Method 1 Method 2 44.2 44.7 23.2 23.0
2. A 25% solution of commercial sodium triphosphate, type 11, was prepared and treated with a saturated sodium chloride solution. The amount of sodium chloride solution added was equivalent to 45% by weight of the sodium triphosphate solution. The sodium triphosphate hexahydrate Jvhich precipitated upon standing overnight was filtered and washed thoroughly with cold Tvater. The product was air-dried. Table I contains the results of the analysis of the tetrasodium pyrophosphate and the sodium triphosphate hexahydrate prepared by the methods described above. DISCUSSION AND DAT4
Variations in the pyrophosphate content of sodium triphosphate-sodium pyrophosphate mixtures have a marked effect on the results of the determination as shown in Table 11. Between 15 and 20y0 sodium pyrophosphate must be present to assure complete precipitation of the pyrophosphate in the presence of sodium triphosphate. If a sample contains more than 25% sodium pyrophosphate, the amount of pyrophosphate apparently recovered is substantially greater than the actual amount present. This is possibly due to occluded sodium dizinc triphosphate. The temperature was maintained a t 25' =t1" C. throughout each of the titrations. The temperature was found to affect both the titration value and the amount of zinc pyrophosphate precipitate. A temperature of 25' C. was found to give the most accurate results. Cale ( 2 ) also found that temperature affects the titration of triphosphate-pyrophosphate mixtures evidently to a much smaller degree than it does with this method, The empirical factor for the calculation of sodium triphosphate as given by Bell ( 1 ) gives high values when applied to the conditions now used for the determination. Calculations of triphosphate and pyrophosphate content are interdependent; the per cent triphosphate found is high when the per cent of pyrophosphate found by precipitation is less than the amount actually present. A change in the triphosphate factor from 0.0258 to 0.0252 serves to correct the difficulty, as shown from the data presented in Table 11. The effect of raising the p H of the triphosphate-pyrophosphate solutions from p H 3.8 to p H 4.5 before addition of the zinc solution was also investigated and m s found to aid in the precipitation of the pyrophosphate. However, zinc hydroxide tends to precipitate excessively during the titration a t the higher p H and is difficult to redissolve. Sodium dizinc triphosphate also tends to precipitate prematurely. Adjustment of the solution to be analyzed to p H 3.8 is therefore recommended. METHOD
Apparatus. Glass electrode p H meter with outside titration assembly and mechanical agitator.
1998
ANALYTICAL CHEMISTRY dium pyrophosphate equals 1 ml. of standard base). If the amount of liberated acid requires more than 28 ml. of 0.1 X sodium hydroxide the pyrophosphate, when determined gravimetrically, will be high and the triphosphate result correNaaPzOl, % spondingly low, After the titration as described in the paragra h 31.4 directly above has been completed, vash t i e 25.0 19.2 titration assenibly off into the beaker contain13.9 ing the precipitate and alloiv the precipitate t o 4.9 settle for 30 t o 60 minutes. Filter, using a rapid 24.26 17.6h paper such as S.and S. 604, and mash the precip10 8 6 itat,e three times with water at room temperature. 5.4h Then reprecipitate the zinc pyrophosphate as 3.06 -2.6C follows : Puncture the filter paper and wash the precipitate into a clean 100-ml. beaker. Any adhering precipitate ma>- be dissolved by washing with 10 ml. of 0.2 A\- hrdrochloric acid. Dilute t o auproximately 250-rh. volume and add sufficieit 0.2 N hydrochloric acid to dissolve all the precipitate. Add 25 nil. of the zinc sulfate reagent and adjust the pH t o exactly 3.8 with 0.1 .\-sodium hydroxide. The pH should be brought back to 3.8 as quickly as possible after dissolving the precipitate t o prevent hydrolysis. -MIOW the precipitate t o settle and filter on S.and S. 604 or similar, fast ashless paper. JVash well with water a t room temperature and ignite the precipitate a t 500" t o 600' C. until theresidueisgray; then a t 900" C. until it is light gray or TThite. T e i g h as ZnpP207. A blank should be run containing no triphosphate and only t h e amount of pyrophosphate added to the sample. Most of the steps in the above procedure are critical. It is therefore necessary to follow each step esactly if accuracy is t o be achieved.
Table II.a Effect of Variations i n Pyrophosphate Content Composition XaaPoOm, % NadPzOr, % 70.0 30 75.0 2.5 80.0 20 85.0 15 90.0 10 80.0
85.0 90.0 95.0 97.0
100.0
6 C
20 15 10
5 3 0
Extra NaaPzOi added from Standard Solution, G r a m None Sone None &*one Kone 0 0750 0 0750 0.0750 0 0750 0 0750 0.0750
Found NasPaOio, % Old factor S e w factor (0.0258) (0.0252) 68.4 76.0 82.4
87.4 97.4 74.5
66.8 74.3 80.6 85 3 96.1 73.3
90.3 96.2
94.5
81.3
98.5
..
79.5
88.3 96 4
Corrected for added Sa4Pz01. Less XarPzOl was recovered than originally added.
Reagents. Sodium hydroxide, 0.1 N . Hydrochloric acid,, 0.2 N . Zinc sulfate, 12.5% solution of zinc sulfate heptahydrate' adjusted to pH 3.8. Bromophenol blue indicator, 0.047, solution. Standard tetrasodium pyrophosphate solution, 1.33 grams1 of sodium pyrophosphate per 100 ml. of solution. Procedure. Weigh accurately 0.5 gram of sample and dissolve in 50 ml. of water. Place the sample on the glass electrode assembly, previously rinsed with ca. 1 X hydrochloric acid and adjust t o ea. p H 3.8 with 0.2 N hydrochloric acid. Four drops of the bromophenol blue reagent may be used if desired. Dilute the sample t o 100 =t2 ml. with water and make a final adjustment to exactly p H 3.8 with 0.2 N hydrochloric acid or 0.1 14' sodium hydroxide. The temperature of the solution should be paintained a t 25" i 1" C. throughout the entire titration. Add ( 0 ml. of zinc sulfate solution a t 25" 1" C. and allow the solution t o agitate 1 t o 2 minutes. Titrate to a pH of 3.8 with 0.1 N sodium hydroxide. The entire titration should be carried out slowlr. When a oH of. 3.7 is reached, stop the addition of sodium'hydroxide $nd stir the solution for 2 minutes to allow equilibrium t o be established. Continue the titration t o p H 3.8 by adding small increments of sodium hydroxide. At least 30 seconds should elapse betneen additions. J\-hen it is believed that the end point has been reached, continue agitation for another 2 minutes, If the value of the titration equals 23 ml. i 1 ml. of 0.1 S sodium h\ droxide, the determination may be continued. (-4 small either a meta or an orthophosphate amount-e.g., 1 to 2%-0f may be present without interfering appreciably n ith the results. However, larger amounts will result in a Ion er titration value due to dilution of the sample mith these nontitrating substances.) If the titration is less than 22 nil. of 0.1 -2' sodium hydroxide, it is to be expected that all of the pyrophosphate has not been titrated and therefore has not precipitated. It is then necessary t o repeat the titration, adding a known amount of standard pyrophosphate solution such that the total titration value will lie between 24 and 28 ml. of sodium hydroxide (0.0133 gram of so-
*
Calculation. Corrected weight of ppt. = total weight of ppt. - weight of blank ppt. Corrected titration = total titration - blank titration Corrected weight of ppt. X 0.872 X 100 Weight of sample
=
[Corrected titration - (corrected weight of ppt. 65.5)] 0.0262 X 100 Weight of sample
% Sa4P207
x =
% NajPjOlo
ACKWOW LEDGMEIIT
The authors wish to thank L. F. Audrieth for his helpful suggestions and criticism. LITERATURE CITED
(1) Bell, R. K., AXLL.CHEM.,19, 97 (1947). (2) Cale, IT. R.,Can. Chem. Process Inds., 32, 741 (1949). RECEIVED for review June 23, 1952. Accepted September 5 , 1952.
Identification of Molybdenum and Tungsten Oxides By X - R a y Powder Patterns ARNE RI
~ G N B L I ,GEORG ANDERSSON, BIRGITTA BLOMBERG,
AND LARS KIHLBORG I n s t i t u t e of C h e m i s t r y , Cniuersity of Cppsalo, Vppsala,Sweden
A previous investigation carried out a t this institute ( 7 ) the IN(approximate) compositions and other data were obtained for
the molybdenum and tungsten oxides formed by reducing the trioxides with the corresponding metal a t about 700" and 1000" C., respectively. The phase analyses were partly performed by means of powder photographs, which, however, in several cases could not be interpreted in detail owing to the very complicated x-ray patterns of these substances. Similar investigations have been made by Glemser and Lutz (4)on molybdenum oxides and by Glemser and Sauer (6) on tungsten oxides. The results of these authors are essentially in agreement with those obtained here as regards the number and approximate compositions of the
existing phases. Further studies carried out a t this institute by means of single-crystal methods have revealed the crystal structures of these compounds and in this way also made it possible to determine the accurate compositions of the complicated intermediate oxides (8, 9, 11-13). [For a survey of the results of these investigations see ( I & ) . ] The existence of the following phases was thus established. RTolybdenum oxides: RIoOz, ModO11, M 0 8 0 t a , RIo9OZ6, and 3100s Tungstenoxides: j\-02,IT,^^,^, \\7,,0ss, and l\-Os The considerable technical importance of the molybdenum and tungsten oxides has caused the authors t o investigate
