February, 1946 A N A L Y T I C A L EDITION 111

A C K N O W L E D G M E N I

Table IV. Refractive Index, M o l e Per Cent Hydrocarbon Composition Data for Figure 1 for System Acknowledgment is due D. Quiggle, S. Lawroski , and Moth ylcyclohexane-Toluene-Aniline

Mole 7 Methyl- cscloRexane0 I1 <I Y 20 2 30 3 40 0 49 05 59.4 7 0 . 1 78 4 90 0 members of the staff of the w,t.

i n 70 aniline ternary 0 5

. 10 15 20 25 30 35 40 4 5 50 55 GO 65 io 75 80 82

Refracti? I 4969 1.4874 1.4784 1.4700 1.5006 1.4914 1.4831 1.4747 1.5045 1.4957 1.4878 1.4795 1.5085 1,5000 1.4926 1.4845 1.5125 1.5046 1.4974 1.4896 1.5168 1,5091 1.5024 1.4947 1.5211 1.5138 1 5073 1.4999 1.5255 1.5185 1.5124 1.5053 1.5300 1.5233 1.5175 1.5108 1.5345 1.5281 1.5227 1.5164 1.5391 1.5330 1.5281 1.5221 1.5437 1.5381 1.5336 1.5280 1.5483 1.5432 1.5392 1.5340 1.5528 1.5483 1.5449 1.5401 1.5574 1.5537 1.5506 1.5463 1.5620 1.5589 1.5564 1.5526 1.5667 1.5641 1.5622 1.5589 1,5686 1,5663 1.5645 1.5615

Composition of hydrocarbon mixture on binary basis.

re Index of Ternary 1.4621 1.4552 1.4671 1.4601 1.4723 1.4653 1.4777 1.4709 1.4831 1.4767 1.4887 1.4827 1.4944 1.4889 1.5000 1.4950 1.5059 1.5013 1.5119 1.5076 1.5181 1.5140 1.5243 1.5205 1.5308 1.5271 1.5373 1.5339 1.5441 1.5409 1.5509 1.5480 1.5578 1.5553 1.5605 1.5583

mined. Curves were easily fitted to the experimental points which are given in Table 111. Since the weight per cent aniline was the desired parametcr in this work, a cross plot was made, taking points from the curves at each 5 weight per cent aniline. These data, given in Table IV, provided nine points to establish rach curve in Figure 1.

The curves in Figure 1 are not straight lines as is sometimes assumed. Charts similar to Figure 1 can be constructed com- pletely on a mole basis or on a weight basis by converting the data in Table IV to the desired values.

Mixture 1.4479 1.4408 1.4355 1.4530 1.4461 1.4406 1.4585 1.4517 1.4462 1.4642 1.4577 1.4522 1.4701 1.4639 1.4585 1.4761 1.4700 1.4650 1.4823 1.4765 1.4717 1.4887 1.4829 1.4786 1.4953 1.4895 1.4857 1.5020 1.4964 1.4929 1.5088 1.5037 1.5004 1.5158 1.5111 1,5081 1.5229 1.5188 1.5160 1.5302 1 5267 1.5242 1.5377 1,5348 1.5326 1.5455 1.5429 1.5410 1.5534 1.5512 1.5496 1 ,5565 1 . ,5545 1.5831

1 ,4285 1.4337 i ,4394 1.4455 1 4522

Petroleum Refining Labora- tory for suggestions and help in the purification of the m a t e rials uscrl.

C O N C L U S I O N S

Ternary mixtures of methyl- I' y c 1 o he x a n e- toluene-aniline can be analyzed rapidly and with good accuracy by read- ing the refractive index of the ternary mixture, followed by reading thc refractive index of the hydrocarbon portion of the mixture after the aniline has been removed.

The same procedure may be useful for analyzing othcr types of hydrorarhon-solvent systems.

LITERATURE CITED

(1) Varteressian, K. A , , and Fenske, M. R. , IND. ENG. CHEM., 28 928 (1936).

(2) Ibid., 29, 270 (1937).

SUBMITTED by Carl 9. Carlson t o the Graduate School of the Pennsylvania S ta te College in partial fulfillment of the requirements for the degree of doo- tor of philosophy.

Rapid Photometric Determination of Iron in Aluminum Alloys

MICHAEL STEVENS PEP1 Metallurgical Laboratory, Ranger Aircraft Engines Division, Fairchild Engine and Airplane Corporation, Farmingdale, L. I., N. Y.

A method for the photometric determination of iron in aluminum alloys i s based on the reaction of ferrous iron and 1 ,I O-phenanthro- line. The information given in this report i s concerned with the for- mation, stability, and reproducibility of the reaction of ferrous iron and 1 ,lo-phenanthroline. The method i s rapid and the accuracy obtained i s t0.05% of the amount present.

NUMBER of papers (1, 5, 5, 7 ) have described the use of 1,- A 10-phenanthroline in the photometric determination of iron in foods, iron ores, and biological materials.

Smith and Richter summarized work done with 1,lO-phenan- throline up to 1944 (6).

done with the mothod of Drenaration ( 2 ) . Blau gave a description of the properties of 1,lO-phenanthroline

Walden. Hammett. and eh:Lpman showed that' thc complex ion formed With fcrrouk iron and 1,lO-phenanthroline has B high oxidation potential and may be used as an indicator in certain oxidimet'ric procedures ( 7 ) . Saywell and Cunningham developed a photometric method for determining small amounts of iron in fruit. juices (5) . In the field of metallurgical analysis, hlehlig and Hulett described a method for the photonictric determination of iron in iron ores ( 3 ) .

The purpose of the work described in this paper was the de- velopment of a rapid and accurate method for the determination of iron in aluminum alloys based upon the formation of ferrous phenanthroline complex.

EXPERIMENTAL W O R K

The reaction of 1,lO-phenanthroline and ferrous iron is the basis for the work described in this paper. At the time of the in-

vestigation, there were no known published papers describing the use of 1,lO-phenanthroline in the determination of iron in aluminum alloys.

The reaction of 1,lO-phenanthroline and ferrous iron produced an orange colored solution, the color intensity varying with the iron content.

Rlethods for dissolving aluminum were investigated. Hydro- chloric acid (1 to 1) was found to be the best solvent for this pur- pose; it also aided in the removal of interfering ions, which are insoluble in hydrochloric acid. If sodium hydroxide mere used, hydroxylamine hydrochloride when added would act as an oxi- dizer of iron instead of a reductant (4).

The following were the available reductants: 10% aqueous solution of hydroxylamine hydrochloride, 0.25 molar solution of stannous chloride, 10% solution of sodium sulfite, formaldehyde, and hydroquinone. The 10% solution of hydroxylamine hydro- chloride proved to be the best, as appreciable errors showed up when the other reductants were used. This was due to the com- plexes formed with iron which kept the 1,lO-phenanthroline from reacting completely with it.

All spectrophotometric measurements were made with the Coleman Universal spectrophotometer Model 11; the cell thick- ness for this instrument is 13 mm. For routine work the Fisher AC Model electrophotometer may be used with a filter of 490 mp; the cell thickness is 23 mm.

To determine the wave length which would produce the maxi- mum absorption, a representative concentration of the solution was examined a t a series of wave lengths. The peak of absorp- tion when using the Coleman spectrophotometer is a t 490 mp The representative sample used contained 0.50% iron.

A series of photometric measurements showed that 15 minutes after the 1,lO-phenanthroline was added the color became stable and remained so for a t least 48 hours. The tests were discon- tinued a t the end of this period.

112 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 Vol. 18, No. 2

Very few ions interfere with the determination of iron in alu- minum alloys. Fortune and Mellon made an exhaustive general study of ions which interfere with the reaction of ferrous iron and 1,lO-phenanthroline. The writer found that silicon, copper, and bismuth interfere with the determination of iron in aluminum alloys (z), but these elements are insoluble in hydrochloric acid and, therefore, can be removed by filtration. Zinc forms a pre- cipitate with &IO-phenanthroline. With small amounts of zinc, it was possible to prevent appreciable interference by adding a slight excess of 1,lO-phenanthroline. Unless the concentration of zinc was greater than 10 parts per million it caused no appre- ciable error. The absence of interfering ions makes the method ideal for rapid, routine work.

REAGENTS REQUIRED

HYDROCHLORIC ACID (1 to l), 1000 ml. of distilled water and 1000 ml. of C.P. hydrochloric acid (specific gravity 1.19).

HYDROXYLAMINE HYDROCHLORIDE (10%). Dissolve 10 grams of C.P. hydroxylamine hydrochloride crystals in 100 ml. of dis- tilled water. Do not use if the solution (Store in refrigerator. has a brown color.)

~ ,~~-PHENANTHROLINE (0.257,). Dissolve 0.500 gram of C.P. 1,lO-phenanthroline monohydrate crystals in 150 ml. of boiling distilled water. Cool. transfer to a 200-ml. volumetric flask, -and dilute with distilled water. (Store in refrigerator. Do not use if the solution has a brown color, as this indicates decomposition.)

Dissolve 1.000 gram of pure iron wire in 50 ml. of concentrated hydrochloric acid. Transfer to a 1000-ml. volumetric flask. Dilute to the mark with distilled water (1 ml. = 0.1% iron or 0.001 gram of iron).

STASDARD IRON SOLUTION.

Beer’s law was followed by the color system, as shown by the straight line obtained when the readings of the observed trans- mittancies at 490 mp for the solution containing up to 5 00% iron were plotted logarithmically.

DISCUSSION

The formation of the complex when ferrous iron reacts with 1,lO-phenanthroline is represented by the radical: (C12H8N2)S- Fe++. This is an orange-colored compound, formed when 1 molecule of ferrous iron combines with 3 molecules of 1,lO-phe- nanthroline.

The basic reaction of hydrochloric acid and the sample does not form any ferric iron, but, upon heating, some of the ferrous iron may be converted to the ferric state. The addition of the reductant, hydroxylamine hydrochloride, converts this ferric iron t o ferrous. The reverse occurred when the sample of aluminum was dissolved in sodium hydroxide; instead of hydroxylamine hydrochloride acting as a reductant, it became an oxidizer of iron. This method compares favorably with other methods of determin- ing iron in aluminum alloys.

An important advantage over other photometric methods for determination of iron is that the pH need not be regulated closely. However, the ferrous color will not develop at a pH much below 2, and the reduction of iron with hydroxylamine is slow at a pH much above 3. The color formation occurs in the acid solution, eliminating the difficulties usually caused by precipitation of metal hydroxides and hydrated oxides in alkaline solution. An- other advantage is freedom from interference of diverse ions.

Table 1. Comparison

Sample No.

114B 85 86B

4064 3044 2624 9193

N1218 N122R

of 1 ,lo-Phenanthroline and Other Methods

Other Methodsa %

0.66 0 . 3 8 1 .52 0 . 3 3 0 . 6 8 0 . 8 0 0.32 0 .98 1 . 0 2

Photometric Method

1,lO-Phenanthroline Photometric Method

%

. .__.

Each value is an average of 12 determinations.

a Permanganate and dichromate methods.

0 .66 0.39 1 .53 0 .33 0.67 0 . 8 0 0 .33 0 . 9 8 1 .00

METHOD

Dissolve a 0.500-gram sample of aluminum in 30 ml. of hydro- chloric acid (1 to l), using a 250-ml. beaker and heating if neces- sary. Filter into a 500-ml. volumetric flask, using Whatman No. 41 filter paper. Wash five times lvith hot distilled water, cool, and dilute to mark with distilled water. Pipet 10 ml. of solution jnto a 100-ml. volumetric flask if the sample contains up to 0.507, iron. Pipet 5 ml. of solution into a 100-ml. volumetric flask if the sample contains over 0.50% iron. Add 1 ml. of hyroxylamine hydrochloride (10%) and mix. Add approximately 70 ml. of dis- tilled water and mix. Add 10 ml. of 1,lO-phenanthroline (0.25%) and mix. Dilute to the mark with distilled water, shake thor- oughly, and let stand for a t least 15 minutes. Using the Coleman spectrophotometer, set the wave length dial a t 490 and measure the color density of the solution. If a Fisher electrophotometer is used, a 490 mp filter is required. Use distilled water as refer- ence solution.

A shortage of standard samples made it necessary to develop a method by which a pure iron solution could be used. This was possible because of the absence of interfering elements. A 1.000- gram sample of pure iron wire was dissolved in 50 ml. of concen- trated hydrochloric acid, then transferred to a 1000-ml. volumet- ric flask and diluted to the mark viith distilled water (1 ml. = 0.1% iron or 0.001 gram of iron).

All results obtained in this study were calculated on the basis The percentage of a pure iron solution standard (Table I).

error was approximately t0.057, of the amount present.

SUMMARY

The reaction of 1,lO-phenanthroline and ferrous iron produces an orange-colored complex. Any ferric iron present is reduced with hydroxylamine hydrochloride.

Silicon, copper, and bismuth are the most common elements present in alumi- num alloys which interfere with the formation of the ferrous- phenanthroline complex, but they are eliminated by filtration because they are insoluble in the solvent for aluminum.

Tests prove that the color reaction is stable for a t least 48 hours, thus confirming the observations of other workers.

The wave length of 490 mp produces the maximum absorption of these instruments.

Representative samples, analyzed and plotted logarithmically, prove Beer’s law holds for the concentrations employed.

An accuracy of *0.05% is possible with this method. I t is more rapid than the standard volumetric or gravimetric methods for determining iron in aluminum alloys.

F7ery few ions interfere with the color reaction.

ACKNOWLEDGMENT

The author wishes to express his appreciation to Richard B. Faurote, chief chemist, for his interest and helpful criticism during the development of this method.

LITERATURE CITED

(1) Blau, F., Monatsh., 19, 648 (1898). (2) Fortune, W. B., and Mellon, bl. G., ISD. ESG. CHEY., ANAL. ED.,

10, 60-4 (1938). 13) Mehlia, J. P., and Hulett, H . B., Ibid., 14, 869-71 (1942). (4) Xlello;, J. IT., “Comprehensive Treatise on Inorganic and Theo-

retical Chemistry”, 1-01, XIV, pp. 80, 81, London, Longmans, Green & Co., 1985.

(5 ) Saywell, L. G., and Cunningham, B. B., IXD. ENG. CHEM., AN.4L. ED., 9, 67 (1937).

(6) Smith, G. F., and Richter, F. P., “Phenanthroline and Substi- tuted Phenanthroline Indicators”, Columbus, Ohio, G. Freder- ick Smith Chemical Co., 1944.

(7) Xalden, G. H., Hammett. L. P., and Chapman, R. P., J . Am. Chem. SOC., 53, 3908 (1931).