c
24
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEVII. TALLOW Original
.. 54
Fraction % Iodine v h u e (Wijs)
High-Titer 40
31
65
Approximate Composition
ro
% Tristearin Distearin monoolein Monosteirin, diolein Triolein
18 32 46 4
Low-Titer 60
Free fatty acid Oleic Stearic
9 5 plus
5 minus
segregation of the fat itself. Typical data are given in Table
VI1 for a sample of tallow (not the same as that shown in Table V). While Tables 11,111,and IV may be employed to show the fallacy of the use of iodine values to calculate the composition of a mixed fat, this has been done in Table 1-11 to give an approximate composition. It was assumed that tri- and distearin constituted the high-titer fraction, while tri- and diolein formed the low-titer component. A more accurate result could be obtained by segregating the fat as shown, then obtaining the separated fatty acids from each fraction, and segregating them. The term “stearin” and “olein” may include homologs of stearic and oleic acids.
Vol. 13, No. 1
A similar segregation of the “adulterated tallow” (Table VI), with similar calculations, shows a higher percentage of both tristearin and of triolein, with smaller amounts of the intermediate compounds. The mixture of olive oil and tristearin indicates its composition definitely when separated in this manner. This segregation method map also be applied to a fat as such in order to determine the nature of the free fatty acid. From the acid numbers of the original fat and of the highand low-titer fractions, it was found that the free acids of the tallow of Table VI1 were over 95 per cent oleic acid. A less direct method also may be used, titrating the free acids, extracting them as soap, liberating them as acids, and segregating. Literature Cited Brown and Stoner. J . Am. Chem. SOC..59.. 3 (19371. > , Hartsuch, P. J., I b i d , 61, 1142 (1939). Irwin, W H., 1x11.EXGCHEM Anal. Ed., 8, 233 (1936). Kass and Burr, J . Am. Chem. Soc., 61, 1062 (1939). Xu, P. S., IND. ENG.CHEM.,Anal. Ed., 9, 103 (1937). Lewkowitsch, “Chemical Technology and Analysis of Oils, Fats and Waxes”, Vol. I, p. 610, London, Maomillan Co., 1921. Skellen, J. H., J . SOC.Chem. Ind.,50, 131T (1931). ~
Quantitative Determination of Phosphorus in Phosphor Bronze A Spectrographic Study WM. E. MILLIGAN AND WALTER D. FRANCE Hanimond Metallurgical Laboratory, Yale University, New Haven, Conn.
An investigation of the spectrographic determination of phosphorus in copper-tin alloys which have been deoxidized with Phos-copper is described. The essential requirement of arc currents of high amperage, of the order of 10 amperes, is demonstrated. The effect of other factors on the characteristics of the arc is presented, and photometric methods of measuring line intensities are discussed. The resulting arc temperatures eliminated the use of solid metallic electrodes and required the use of the standard regraphitized carbon electrodes with a 200mg. sample. The proposed method makes possible the spectrographic determination of 0.001 per cent of phosphorus in these alloys, with an accuracy of * 5 per cent.
T
HE increasing application of the spectrograph to quantitative determinations of compositional variations of industrial raw materials has been very striking in the past decade, although applications appear to have been relatively few with respect to certain insensitive elements, particularly carbon, sulfur, and phosphorus. Phosphorus was selected for study, since for many years it has been the major tieoxi-
dizer for the copper-tin alloys. Such alloys carry percentages of phosphorus particularly applicable to spectrographic determination, roughly in the range from a trace to 0.50 per cent. A review of the literature reveals a lack of information on the spectrographic analysis of phosphorus. One reason for this is probably found in a list of arc sensitivities of 50 elements developed by Ryde and Jenkins (11) in which phosphorus was assigned an arc sensitivity between 2 and 3. By definition, therefore, a sensitivity of 2 is equivalent to 1 part in 100 or 1 per cent, while that of 3 is equivalent to 1 part in 1000 or 0.10 per cent. Recently Rollwagen and Ruthardt (IO),reporting on the spectrographic analysis of a platinum alloy containing 0.005 per cent of phosphorus, announced tbe detection of the phosphorus lines of X 2535.65 and X 2553.28 A. (All wave lengths used are those given by Harrison, 5 . ) This result was secured when solid electrodes were excited by a direct current arc of 12 amperes a t 110-volt potential. Condensed spark excitation, on the other hand, in the case of a similar alloy containing as much as 0.10 per cent of phosphorus, pr:duced a positive record of the strong line at X 2535.65 A,, with the next sensitive line 2553.28 A. barely visible. The arc data more nearly coincide with American practice, since the detection of phosphorus in bronze has been extended beyond the 0.10 per cent claimed by Ryde and Jenkins (11). Subsequent to the initiation of the experimental work, Pierce, Torres, and Marshall (9) reported negative results with respect to phosphorus in a sample of pig iron containing by chemical analysis 0.08 per cent of phosphorus. More recently, Gregg and Irish (4) have again noted the insensitivity
January 15, 1941
ANALYTICAL EDITION
25
of carbon, sulfur, and phosphorus in ferrous products. The negative statements previously quoted, together with the absence of any mention of phosphorus determinations in many recent articles on spectrographic analysis of steel and iron products, would appear t o have established the insensitivity of that element by this method of analysis. Despite the apparent general belief in the insensitivity of phosphorus, spectrographically, it was decided to investigate the possibility of extension of the range of determination of this element in low-phosphorus bronzes of the 95-5 or Grade A type. Apparatus The spectrograph available for the investigation was of the large Littrow type as manufactured by the Bausch & Lomb Optical Companx. The dispersion in the operation range was of the order of 2.5 A. per mm. The instrument was equipped with a standard Bausch & Lomb 220-volt direct current arc excitation system. However, in the course of experiment, the standard resistance was discarded in favor of a more flexible and extensive one, giving a range from 1 to 20 amperes. Eastman S o . 33 plates were used throughout. All plates were developed under standard conditions of time and temperature, with developer of Eastman D-11 formula. The plates were calibrated by using a standard Bausch & Lomb sector disk of a step ratio of 1 to 1.5, rotated by a constant-speed, split-phase motor of 1800 revolutions per minute. This figure was established by measurements with a tachometer stroboscope.
low a content of 0.10 per cent. It was concluded that increased sensitivity might be obtained a t amperages well above the 4.5 employed. Accordingly, sample 3 (0.067 per cent phosphorus) was exposed under similar conditions with the exception of increased amperage. The results were positive. Later, additional plates were taken of alloys of even lower phosphorus content, with the final plate obtained when a new sample of 0.001 per cent phosphorus alloy was exposed at amperages of 8, 10, and 1,2. This plate indicated that the phosphorus line X 2534.01 A. was barely visible for the latter two exposures. Observations of experimental conditions indicated the essentials of consistent results to be a function of several variables. The effect of increasing the amperage from 10 to 12 is not so great as might be expected, since the negative effect of the mechanical ejection of small globules from the sample is greatly increased. This is not opposed to the findings of Slavin ( I S ) , mho recently correlated the increase in emission with increase in amperage when operating his fed iron arc. Duffendack and his co-workers ( 3 ) showed the importance of studying the effect of variations in arc current. It was decided to make all future determinations on arcs employing a current of 10 amperes.
Excitation A range of analyzed phosphor bronze samples was gener-
This factor mas studied using a range of samples weighing 5 , 10, 20, 50, 100, 200, and 500 mg. Observations made during the excitation period indicated that less mechanical loss was occasioned with the three higher weights. The spectra showed slight choice between the exposures made with 100 and 200 mg. However, better sampling conditions prompted the choice of 200 mg. The 500-mg. sample would require a larger cup. The authors' conditions were definitely unsatisfactory for small weights, since in some cases all of the sample was ejected on striking the arc or after a relatively short portion of the exposure was made. It is possible t h a t smallerdiameter rods and different-dimensioned cups might overcome this difficulty.
ously supplied by the Scovill Manufacturing Company. These samples differed widely in form, as drillings, millings, and thin sheet, and it was early rehlized that the method of excitation employed must be prepared to accommodate this dissimilarity in form. The choice appeared t o be limited t o the carbon arc electrode. Smith ( 1 4 ) reported extensively on this method when applied to analysis of impurities in lead. Brownsdon and van Someren ( 2 ) described a technique using a copper rod 3 cm. in diameter as a positive sample container. Hitchen (6) detailed the use of carbon rods in the quantitative spectrographic determination of impurities in tin. It remained for Milbourn ( 8 ) to investigate comprehensively and establish the increased sensitivity of the globule arc method with a carbon electrode. He recommended a sample between 0.20 and 0.50 gram, using a positive copper electrode and a negative carbon rod-supported globule. In this way, Milbourn was able to detect small percentages of bismuth, arsenic, lead, antimony, and tin, whereas under similar conditions of excitation no traces of these elements were detectable with metallic solid electrodes.
It mas concluded from the above evidence that increased sensitivity of phosphorus might be expected from some modification of the globule arc method of excitation, particularly in view of the close periodic group relationship with several of the previously mentioned elements. Preliminary experimental work was initiated with the object of verifying this assumption. I t was decide4 to examine the egect on the sensitivity of the lines X 2534.01 A. and X 2554.93 A. when amperage, weight of sample, and length and portion of arc were varied, employing Acheson regraphitized carbon electrodes of 0.78-em. (0.31-inch) diameter. The positive electrode cups were drilled to a depth of 3.0 mm. with wall thickness of 0.75 mni., then purified by the solution method of Standen and Kovach (15). The upper negative carbon electrodes were pointed in a pencil sharpener and similarly purified. Current in -Arc A series of exposures of six analyzed samples ranging from 0.25 to 0.008 per cent phosphorus, of 250-mg. mass, were excited for 4 minutes, a t 4.5 amperes, with the plain sector disk set to expose the plate for one fourth of that interval. The slit width was maintained constant a t 15 microns for all exposures. This plate reyealed no evidence of phosphorus be-
Mass of Sample
Length and Fraction of Arc Registered Efforts in this direction were confined to several plates. The first investigated the effect of variation of electrode spacings of 1, 2, and 3 mm. This effect was negligible, and since manipulation of the image of the arc on the slit was less difficult a t 3 mm., all subsequent exposures were made with that setting. Continual adjustment of the electrodes is required because of their rapid rate of combustion when such high currents are used, Increasing this spacing appreciably beyond this figure diminishes the current amperage with resultant critical diminution in intensity of emission. Evidence was developed to indicate that a reduction of 1.0 ampere between 10 and 9 amperes was sufficient to eliminate all trace of phosphorus lines in spectra produced from arc excitation of samples containing phosphorus of the order of 0.001 per cent. It mas further noted, under the prevailing conditions of excitation, that a period of 15 seconds was required to melt the material and to establish a steady arc. To determine whether this procedure introduced loss of phosphorus, two plat'es were taken with a continuous series of exposures covering excitat'ion for 8 minutes. The samples selected for this multiple exposure contained 0.008 and 0.19 per cent of phosphorus, respectively. Examination of t'hese spectra showed that for each concentration the line intensities were the same for the first 3 minutes. I n both cases, traces of phosphorus were detected even after 5 minutes of excitation. The absence of traces of phosphorus after that period was attributed to the mechanical ejection of the globule. The persistency of pliosplionis lines in the spectra of both series n-ai surprising.
26
INDUSTRIAL AND ENGINEERING CHEMISTRY
intensities has been treated in several different ways. Mankowich (7) evolved one procedure in which he defined opacity as equal to: clear plate reading - zero reading molybdenum line reading - zero reading
I0
I0
14
when determining molybdenum in an alloy steel. A working curve was then plotted using log opacity against log concentration. Brode ( 1 ) adopted a method of plotting log of intensity ratios against log of concentration. I n this case, intensity is clear plate deflection less line image deflection, with the intensity ratio that between the unknown and an internal standard line. Strock (17) established what he designated as a blackening curve in which I D (density) = log 2 I
12
D
Vol. 13, No. 1
IO
00
06
04
a7 0
02
04
Ob
LOG
OS
10
I2
Id
IS
EXPOSURE
FIGURE 1. TYPICAL BLACKENING CURVE
Summary of Excitation and Development The foregoing results were interpreted to indicate the following method of operation.
A 200-mg. sample of material, drillings, millings, or otherwise, was weighedout on an analytical balance,and transferred to a 0.78cm. (0.31-inch) regraphitized rod, which was cupped t o a depth of 3 mm. with wide walls of 0.75 mm. This container was made the lower and positive electrode while the negative electrode was a rod, similar in composition and diameter, but pointed. The space between electrodes was carefully adjusted t o 3 mm. and the rheostat adjusted t o yield an arc of 10 amperes. The arc was struck and the final adjustment of current was made t o give exactly 10 amperes on the ammeter scale. The plate exposure was started after an interval of 15 seconds and continued for 1 minute. A constant current of 10 amperes was maintained throughout the exposure period. The final spectrum of each plate was for calibration and was obtained by exposure of a similar sample but with the step sector rotatin in-front of the slit. All pfates used were of the standard Eastman 33 type and were develoDed for 5 minutes with Eastman D-11developer at a temperat&e of 18.3" C. (65" F,). (Mechanical loss is always encountered in excitation of this high current density, but it was believed from observation that this effect was reduced t o a constant minimum value.)
Microphotometer Plate Calibration
a method using a step slit, while Strock (17) has detailed a step sector procedure. The
where D is blackening or optical density, 10 is the galvanometer deflection when this reading represents a measure of the difference between a completely unexposed portion of the plate or clear plate and of the zero setting of the instrument or that for a completely exposed portion of the plate (maximum blackness), and I is the difference between zero setting and the reading for the blackening of the image of the desired line. From the microphotometer readings, values of D are calculated and are plotted against the log of the relative exposures. These are obtained by calculation involving the use of the characteristic factor of the step sector and the particular step. Such a curve is shown in Figure 1,while the plotted data appear in Table I. TABLEI. BLACKENING Step (No. 1, smallest 8 1 2 3 4 5 6 7 ope~1ng) Relativeexposure 1.00 1.50 2.25 3.38 6 . 0 7 7 . 6 0 11.1 16.7 0 0.170 0.352 0.529 0.705 0.881 1.045 1.223 Log of exposure
I n order to compensate for slight variations in excitation and photographic conditions, i t is customary to plot the log of the intensity ratio of a line of the unknown against a line of some internal standard element. The region of the spectra in which the strong lines of phosphorus are located, is not particularly favorable for the selection of a suitable comparison line, However, several lines of the major elements (copper and tin) were selected and measured photometrically and the log of the resulting intensity ratio was plotted. Only three of the sensitive phosphorus lines, X 2534.01, X 2553.28, and X 2554.93 A., were used. The line X 2535.65 8. was discarded becavse of the proximity of the high intensity iron line,
X 2535.604 A. The most consistent results were obtained when the inten-
ANALYTICAL EDITION
January 15, 1941
standard. This line is not entirely free from objections; it would have been more desirable a t somewhat longer wave length, although there is no other closer copper line. The, intensity is relatively high as compared to that of the phosphorus lines. On the other hand, the existence of 95 per cent of the alloy as copper ensures freedom from variations due to changes in composition. There are several lines of tin in this region, but these-were discarded, since it was planned to investigate subsequently alloys of lower tin content. 0 ,
I
I
I
I
I
I
I
I
27
This approach to a straight-line condition is lost through bending of the curve a t a concentration of above 0.03 per cent phosphorus. Apparently, the high amperage excitation current so essential to produce any trace of phosphorus in alloys of lower content is no longer necessary. Strock (16) discussed in great detail the factors which coiitribute to such variations, emphasizing the dependence of exposure on two factors-time and the intensity of the light. This explains the authors’ ability to detect traces of phosphorus in the original experimental plate when the content was in the range above 0.03 per cent and the excitation amperage was approximately 4.5. I p 2531 Figure 3 shorn two curves, plotting log against concentration. Curve 1is that for standard phosphor bronze alloy, while S o . 2 is a phosphorized Admiralty, containing 28.0 per cent zinc, approximately 1.2 per cent tin, and small quantities of phosphorus. This shifting of the curve has been attributed to the presence of high percentages of zinc. Similar phenomena have been obtained by many workers in this field.
Conclusioii The determination of the quantitative spectrographic analysis of phosphorus in phosphor bronze has been investigated. Evidence indicates the possibility of estimating phosphorus in amounts of the order of 0.001 per cent or higher, using the globule arc method with high excitation amperage. An accuracy of * 5 per cent is claimed for this method. 0
01
.02
03
PERCENT
.04
.OS
06
07
08
Acknowledgments
PHOSPHORUS
FIGURE 3
After the blackening curve for a plate was constructed, the D values of the measured spectral lines were calculated from the microphotometer readings. Using these calculated values the intensities of the lines were taken from the blackening curve, and then intensity ratios of the desired lines nrere calculated. The log of these intensity ratios was then plotted against per cent concentration. The working curve was made I by plotting log 2 against log of per cent phosphorus. Three Icu of these curves were developed using the three previously mentioned phosphorus lines against the same value for the copper line X 2441.6 A.
Discussion of Curve All three phosphorus lines yielded working curves of satisfactory value. However, since the curve obtained on plotting Ip2834 J which is the weakest line of phosphorus, was log I c u 2441.6 usable a t the authors’ lowest concentration, and the resulting plot more nearly approached a straight line, that curve only has been shown in Figure 2. Data for the curve appear in Table 11.
0.008 0 , 0 1 6 11.5 G.6 1.061 0.819 0.301 0.488 0.730 0.09 0.2s 0.50 cu, deflection, cm. 0 . 9 0.9 0.8 cu, log of deflection 0,046 0.046 0.097 1.595 1 , 6 4 6 D (calcd.) 1,595 I C ” (from Fiz. 1) 1 35 1 , 3 5 1.39 0.067 0 , 2 0 7 0.360 IP/I’CU 1.174 Log I P / I C n 0.684 0.444 0.001 17.7 1.248
0.030 4.1 0.613 0,936
0.70
0.7
0.155 1.704
0.100 2.3 0.361
1.187 0.89 0.8 0.097 1.646 1.39
1.45 0.482 0.640 0.317 0.194
0.190 0.250 1.9 1.3 0 . 2 7 9 0.114 1.270 1,436 1.03 1.19 0.8 :55 0.097 1 . 7 0 4 1.G46 1.45 1.39 0.710 0 . 8 5 5 0.149 0.068
::
The authors wish to express their gratitude to W ,B. Price, F. 3.1. Barry, and R. K. Bailey of the Scovill Uanufacturing Company for their gift of analyzed samples; to B. H. McGar and P. A. Leichtle of the Chase Copper and Brass Workb for permission to use their microphotometer; and to P. A. Leichtle for his kind service in measuring 5ome of the plates.
Literature Cited Brode, W.R., “Chemical Spectroscopy”, Sew York, John Wiley & Sons, 1939. and van Someren, E. H. S., J . Inst. Metals, Brownsdon, H . W., 46, P a r t 2, 97 (1931). Duffendack, 0. S., Wolfe, R . h..and Smith, R. W., ISD. ESG. CHEX.,Anal. Ed., 5, 226 (1933). Gregg, J. L., and Irish, P. R., Iron Age, 195, No. 19, 33 (1940). Harrison, G. R., ‘Wavelength Tables”, New York, John Wiley & Sons, 1939. Hitchen, C. S., Am. Inst. .lfii~ing.Vet. Engrs. Tech. Pub. 494 (1933). Mankowich, Abraham, Jfetuls Le. Alloys, 9, 131-7 (1938). Milbourn, M., J . Inst. Metals, 55, Part 2, 275 (1934). Pierce, W. R . , Torres, 0. R., and Marshall, IT. IT., I s u . ESG. CHEII.,Anal. Ed., 12, 41 (1940). and Rnthardt, K., Jletallwirtschaft, 15, 187-9 Rollwagen, W., (1936). Ryde, J. W.,and Jenkins, H. G., “Sensitive Arc Lines of 50 Elements”, London, Adam Hilger, 1929 (rev. 1930). Scribner, B. F., Proc. Fifth Summer Conference on Spectroscopy, 1937, pp. 51-6, New York, John Wiley & Sons, 1938. Slavin, Morris, ISD. EXG.CHEJI.,Anal. Ed., 12, 131 (1940). Smith, D. M., “Metallurgical Analysis by the Spectrograph”, British Kon-Ferrous Metals Res. Assoc. Monograph 2, p. 87, 1933. Standen, G. IT.,and Kovach, L., A. $. T. A I . Syniposium on Spectrographic Analysis, Proc. Am. SOC.7 e s t i n g 3fateriaZs. 35, Part 2, 33 (1935). Strock, L. W.,Proc. Seventh Summer Conference on Spertroscopy 1939, p. 134, New York, John W l e y & Sons, 1940. Strock, L. IT;., “Spectrum Analysis with the Carbon Arc Layer”. pp. 28-37, London, Adam Hilger, 1936. Thomson, I(.B., and Duffendack, 0. S.,J . Opticul Soc. A m . . 23, 101-4 (1933).
