ANALYTICAL CHEMISTRY
732 precipitating the phosphate with magnesia mixture and igniting to magnesium pyrophosphate. The results in set 3 indicate a slight pickup of phosphorus when the proposed mercury cathodehydrogen sulfide procedure is used. The resulting error caused by this apparent pickup of phosphorus approaches insignificance when a 4-gram sample is used. This error is overcome when the photometer is set a t 100% transmittance with the reagent blank. Table I11 shows typical values of the effect of silicon and arsenic additions on the recovery of phosphorus from the high purity iron sample. The preswce of small amounts of silicon can be tolerated without the use of hvdrofluoric acid, but large amounts make its use mandatory. The addition of 5 ml. of hydrobromic acid (1 to 4) prior to the final perchloric acid fuming will eliminate errors cauwd by the presence of arsenic.
Table 111. Effect of Silicon and Arsenic on Phosphorus Recovery Sample (FeA), Grams
rirsenir Added.
Siliron Added.
Y
Y
fll? Added
Apparent
HUr Added.
phosphor^^
1111.
Y
Reroi.ery,
Sufficient iron may be removed a t this stage to cause no difficulty with the subsequent development of the color complex. The removal of mercury by hydrogen sulfide is necessary because its presence causes turbidity which leads to erroneow transmittancy readings; i t is not sufficient merely to remove tliP metallic mercury by filtration since there are always small amounts of soluble mercury salts found in the electrolyte. As i t is not necessary to remove the iron completely, it should be possible to conduct the electrolysis satisfactorily in a watercooled beaker in the event a water-cooled Melaven cell is not available. The use of perchloric acid for conducting mercury cathode electrolyses is far from new. I n spite of this, the trend seems to favor the use of sulfuric acid. While sulfuric acid may be preferable for some analyses, perchloric acid offers certain advantages with iron and steel samples. Dehydration of steel sample solutions with perchloric acid proceeds rapidly and smoothly xitti no danger of bumping arid spitting, which is not true in the caw of sulfuric acid. h thoroughly dehydrated sample of ferric sulfate is extremely hard to redissolvr upon dilution, whilr ferric perchlorate dissolvrs very readil?-.
... 4
4 4
ACKNOWLEDGMENT
...
400 400 400
2 drops.
...
..
ii J
.i
5.0
Grateful acknowledgment is made to C. AI. Bible, Analytical Chemistry Section, for advice and suggestions during the investigation, and for making available water-cooled mercury cathode cells of hi3 design. LITERATURE CITED
COiMMENTS
K i t h little or no change in technique the method should be applicable to phosphorus microdeterminations in any high-purity element or material that forms soluble perchlorate salts and that may he separated by rlectrolysis with the mercury cathode. While greater sensitivity may be had by measuring the transmittancies a t 830 mp, the sensitivity is great enough to permit the determination of 0.0001% phosphorus on a Cgram sample with a 650 mp filter, which is still used by many laboratories to measure the molybdenum blue complex photometrically. S o attempt was made to determine phosphorus in the electrolyte after the firPt electrolysis with the mercury cathode.
(1) Boltz, D. F., and Mellon, SI. G., IND.ENG.CHEX, ANAL.En.,
10, 873-7 (1947).
(2) Bright, H. A., -4ppendix to Thompson, J. G., and Cleaves, H. E..
J . Research Natl. Bur. Standards, 23, 163-79 (1949). ( 3 ) Hague, J. L., and Bright, H. A., I b i d . , 26, 405-13 (1941).
Kitson, R. E., and Mellon, XI. G., IND.ENG.CHEM.,~ A L ED., . 16, 46G9 (1944). (5) Melaven, A . D., Ibid., 2, 180 (1930). ( 6 ) Rodden, C. J., “Analytical Chemistry of the Manhattan Project,” p. 511, New York, McGraw-Hill Book Co., 1950. (7) Short, H. G., Appendix to Hopkins, B. E., Jenkins, G . C. H., and Stone, H. E. S . . J . Iron Steel Inst. (London), 168, 377-83 (1951). (4)
RECEIVED for reyiea 1 I a y 27. 1 9 3 .
.Arrepted Dei,ember 23. 19.54,
Molar Absorptivity of Dithizoae in Chloroform A. S. LANDRY’ and SILAS FONSECA REDONDO2 Departamento Higiene Industrial, Servicio Cooperativo lnteramericano de SaIud PbbIica, Lima, Per;
I
T IS possible to prepare pure dithiaone solutions of known concentrations b j utilizing the extr‘iction procedure of Cooper and Sullivan ( d ) , thus eliminating the necessity of obtaining the solid dithizone in a highly purified form. This purification is accomplished by stripping the dithizonechloroform solution twice with dilute ammonium hydroxide ( 1 to 100) with volumes equivalent to 10 times the volume of dithizone solution. After removal of the chloroform layer, the aqueous dithizone phase is filtered through a pledget of cotton inserted in the stem of a Squibb funnel into another Squibb. The filtrate is carefully neutralized with metal-free 1 to 1 hydrochloric acid t o precipitate dithizone. which is then re-extracted into chloro1 Consultant. Industrial Hygiene Chemistry, Institute of Inter-American Affairs, % American Embassy, Lima, Peru. 3 Present address, Sen-ipo de Iligiene e seguranca do Trabalho, Secretaria d o Trabalho, Industria e Coinercio. S&o Parilo. Brasil.
form purified according to Bambach and Burkey ( 1 ). The concentration of dithizone in moles per liter may be obtained by dividing the observed absorbancy, A , a t 606 mp by the molar absorptivity a t this wave length, using a cell of 1.0-rm. light path As the result of 25 replicate determinations, the molar absorphas been found to be 40.6 tivity of dithizone in chloroform, f 0.5 X lo3. This was obtained by shaking 25.0 ml. of a dithizone-chloroform solution (4.99 mg. per liter) with an equal volume of an aqueous solution, buffered a t p H 3.4 with potasEium acid phthalate, of known but deficient mercuric content (0.498 X 10-5M). Since mercuric dithizonate does not absorb a t 606 mp, the absorbancy of the miled-color, .45,, is equal to the absorbancy of the excess dithizone, AS,. T h e latter value when subtracted from the absorbancy of the original dithizone solution, AaO,gives the change in abaorbancy, AA8. Dividing the molar concentration of dithizone entering the complex into this change i n absorbancy gives the molar absorptivity, or
V O L U M E 2 6 , NO. 4, A P R I L 1 9 5 4 A further advantage may be obtained from this procedure in the preparation of dithizone solutions of reproducible concentrations. This is readily accomplished through the use of a stock solution prepared by purifying 100 mg. of solid dithizone, dissolving in 100 ml. of chloroform, extracting as indicated with the exception t h a t the ammonia concentration is increased tenfold (1 to lo), and re-extracting into 500 ml. of chloroform a t 20.0' C. Utilizing 25.0- and 40.0-ml. portions of the stock (and 1 to 100 ammonia) produced standard dithizone solutions of 4.4 and 7.1 mg. per liter, respectively, when the final volume n-as 1.0 liter a t 20.0 ' C. These doubly purified solutions were stable, not easily oxidized, had a very narrohv range of variation in concentration,
733 and proved t o be highly satisfactory for use in the determination of cadmium, lead, and mercury. LITERATURE CITED (1) Bambach, K., and Burkey, R. E., IND.ENG.CHEW,ASAL. ED., 14, 904 (1942). (2) Cooper, S. S., and Sullivan, 51.L., ;IN
