224
INDUSTRIAL AND ENGINEERING CHEMISTRY
lent chromium content, as shown by Tables I1 and 111. Inasmuch as these steels have varied in manganese from 0.39 to 4.75%, it is assumed that there is no interference of manganese in the determination of silicon.
Vol. 17, No. 4
ACKNOWLEDGMENT
The authors wish to take this opportunity to express their sincere gratitude to R.David Thomas, Jr., director of research and engineering, for his interest and helpful criticisms throughout this investigation.
SUMMARY
A spectrophotometric determination of silicon in low alloy and stainless steels is described which is rapid and simple, and uses water as a reference sample. The method is subject to interference from chromium only. Using precalibrated curves for various general types of steel, silicon can be determined with an accuracy of *0.04% silicon without correcting for chromium, or +0.020/, when the correction is made. The deviation in the observed percentage of silicon is directly proportional to the concentration of chromium. The method may be used with many of the colorimetry instruments now available.
LITERATURE CITED
(1)
(2) (3) (4)
(5)
Case, 0. P., IND.Ewo. CHEM., ANAL.ED.,16,309 (1944). Hadley, W.H., Analyst, 67, 5-8 (1942). Kahler, H. L., IND. ENQ.CHEM., ANAL.ED.,13,536 (1941) Robinson, R. J., and Spoor, H. J., Ibid., 8, 455 (1936). Schwarts, M . C., I b i d . , 6, 364 (1934).
(6) Zbid., 14, 893 (1942). (7) S c o t t , B. A., Analyst, 67, 389 (1942). ( 8 ) Swank and Mellon. IND.ENG.CHEM..ANAL.ED.. 6. 348 (1934). (9j Urech, P., AnaZyst,’65, 131 (1940); abstracted from Helu.‘Chim. Acta, 22, 1023-6 (1939). (10) Weihrich, R., and Schwartz, W., Arch. Eisenhiitten., 14, 501-3 (1941).
Determination of Gamma-Tocopherol in Vegetable
Oils
G. S. FISHER Southern Regional Research Laboratory, N e w Orleans, La. The details of a method for determining y-tocopherol in the presence
of a-tocopherol b y oxidation with nitric acid in the presence of acetic acid, followed by photometric estimation of the red color produced, are presented with results of its application to several vegetable oils. Use of the method presupposesabsence of 8-tocopherol.
T
BE sntiouygenic activity of the three tocopherols (alpha, beta, and gamma) in fats and oils was recognized (10) shortly after their isolation. It was observed that in the substrate used by Olcott and Emerson (IO) 7-tocopherol has about three times the antioxygenic index of a-tocopherol, and that the activity of 0-tocopherol is intermediate between the other two. However, it h a s been impossible to evaluate quantitatively the protective action afforded natural oils by virtue of the presence of tocopherols, since there has been no satisfactory method of determining the concentrations of the individual tocopherols in the oils. The same limitation has been encountered in attempting to predict the antioyygenic activity of tocopherol concentrates and in correlating vitamin E activity with tocopherol content. The desirability of a method of determining one of the individual tocopherols in the presence of one or both of the others has frequently been stressed (3, 14, 15), but only two methods for the determination of the concentration of an individual tocopherol have been suggested. One of the methods ( 2 ) is based on the difference in rate of oxidation of the three tocopherols by silver nitrate in methyl alcohol solutions; the other (IS) is based on the reaction of -,-tocopherol with diazotized p-nitroaniline to give a red color which is measured colorimetrically. The originators of these methods applied them only to concentrates, derived from natural oils, containing several per cent of tocopherol. I n neither case was the method described in sufficient detail to permit its general use. Smith el al. ( 1 7 ) have suggested the possibility of determining a-tocopherol by polarographic analysis, and Scudi and Buhs (15) have reported that 8- and y-tocopherols, but not a-tocopherol, give red colors when treated with nitrous acid and then treated with a base. No method of analysis has been developed as a result of either suggestion. No vegetable oil has been reported t o contain both 8- and y tocopherol, and only wheat germ oil has been shown t o contain &tocopherol; therefore the principal problem confronting workers in this field is the determination of either a- or y-tocopherol in mixtures containing both these tocopherols. If the concentration of either a- or y-tocopherol can be determined, the concen-
tration of the other tocopherol can then be calculated by (liference between it and the total tocopherol content, for which determination several methods are available (4, 6, 6, 8, 11, 1 2 , 15). The present investigation was undertaken t o develop a method for determining the content of y-tocopherol in a vegetable oil which also contains a-tocopherol. Smith et al. (16) stated with regard t o the oxidation of tocopherols by nitric acid, “An alcohol is necessary as a solvent in order t o produce the red solutions from the tocopherols.. .Red solutions are not formed in petroleum ether, acetic acid, or acetone.” It has been found that this statement applies only to CYtocopherol. Red solutions are formed when either % , or y-tocopherol is treated with nitric acid in acetic acid solution, but CYtocopherol gives only a slightly yellow solution under these conditions. Since the intensity of both the red c‘olor obtained with ytocoplierol and the yellow color obtained with a-tocopherol on treatment with nitricacid isproportional to theconcentrationof tocopherol, i t is possible to determine the amount of ytocopherol in the presence of a-tocopherol by use of a photoelectric colorimeter and the principle of differential spectral separation. The details of a method of determining y-tocopherol by oxidation with nitric acid in the presence of acetic acid, followed by photometric estimation of the red color produced, are presented here, together with the results of its application to several vegetable oils. REAGENTS
The following solvents and reagents are required. SOLVENT, 60 parts by volume of acetic acid (c.P.) mixed with 40 parts by volume of chloroform (c.P. or U.S.P. XII). KITRIC ACID. Concentrated nitric acid is freed from oxides by boiling and stored in the dark until needed. SULFURIC ACID, 85 grams of concentrated sulfuric acid (c.P., density 1.84) added to 15 grams of distilled water. POTASSIUM HYDROXIDE, 1 gram of solid potassium hydroxide dissolved in 100 ml. of distilled water. SKELLYSOLVE B. Skellysolve B is purified by washing it first with successive portions of concentrated sulfuric acid until the sulfuric acid no longer turns brown, then with 1% aqueous potassium hydroxide solution, and finally with distilled water. It is dried with anhydrous sodium sulfate and distilled. TOCOPHEROLS. Synthetic d,l-a-tocopherol (Merck), E;?& (290 mp) 70.0; synthetic d,l-D-tocopherol (Merck)Ei?!, (296 mp) 83.5; and y-tocopherol (Distillation Products, Inc.) Et (296 mp) 92. [The tocopherols were used without further puri-
Fm.
April, 1945
ANALYTICAL EDITION
fication, since the extinction coeffic'ients given are in excellent agreement with those reported by Baxter et al. ( 2 ) for their highly purified products.] OPTICAL EQUIPMENT
A Coleman spectrophotometer, hlodel 10-SDM, 7.5-mfi slit width, 1.25-cm. (0.5-inch) cell is used for determining the spectral characteristics of the oxidation products and an Evelyn colorimeter, equipped with filters 490 and 420: is used for measuring the colors produced by oxidation with nitric acid, from which the concentration of y-tocopherol is calculated. PROCEDURE
DEVELOPMEKT AKD MEASUREMENT OF COLOR. Samples of pure tocopherols or oils which are free from interfering pigments are weighed directly into the absorption cell or colorimeter tube and diluted to exactly 9.6 ml. with a mixture of acetic acid and chloroform (3 to 2). The tube is placed in the colorimeter with filter 420 in place, and the light intensity is adjusted to give a galvanometer reading of 100. The tube is then removed, and the galvanometer reading with no tube in the holder (center setting) is recorded. Filter 490- is substituted for filter 420, and the center setting for this filter is determined in the same way; 0.4 ml. of nitric acid is then added to the tocopherol solution with shaking; the light intensity is adjusted to give the proper center setting with filter 490; 30 seconds later the colorimeter tube is inserted, and the galvanometer reading is recorded. The filter is then chaneed, and after the center setting is readjusted and the tube containing the sample is inserted, the galvanometer reading is recorded. The L values corresponding to the recorded galvanometer readin s are calculated from the equation L = 2 log G, in which is the galvanometer reading. The sample used should contain 0.20 to 2.00 mg. of y-tocopherol. The absorption of light by the oxidation CALCULATIONS. product of a-tocopherol is too great to permit the general use of sin le filter photometry. Hence, the method of differential s ec tray separation proposed by Knudson ( 7 ) , Ashley (I), and otgers (19, 20) must be used to calculate the concentration of y-tocopherol. The necessary equations are:
8
= Ky490Cy
+ Ka4"Ca
(1)
L42u= K y 4 W y
+ Ka'Wa
(2)
L490
and solving Equations 1 and 2 for Cy
emulsion which forms. The supernatant liquid is then transferred to another centrifuge tube, washed with about 20 nil. of 1% potassium hydroxide solution, and again crntrifuged (ca. 10 minutes at 1500 r.p.m.). Suitable aliquots of thd Slielly?olve B layer are transferred to the colorimeter tube, arid the solvent is removed by evaporation on a steam bath, preferably in an inert atmosphere. The color development and measurenient are then carried out on the residual oil, as previously desribcd. This treatment also serves to remove both the peroxides and tocoquinones (15) from artly oxidized oils. ~.4PosmcaTIoN #ROCEDURE. Since quantities of oil greater than 1.5 grams do not yield homogeneous solutions after the addition of the nitric acid, very dilute solutions of y-tocopherol in oil are concentrated by saponification in the presence of pyrogallol as a protective a ent ( 9 ) , followed by estrnction of the unsaponifiable matter wit! peroxide-free ether in the usual manner. The ether extract is dried and made up to a suitable volumee.g., 100 mi. Aliquots are transferred t o the colorimeter tube, the solvent is removed, and the color is developed and nieasureti as described. The concentration of y-tocopherol in the oil is calculated directly, since the weight of oil represented by the aliquot. is known. It is unnecessary to weigh thc unsapoiiifiablc mattw. RESULTS A N D DISCUSSION
SPECTRAL ABSORPTIOK.The spectral absorption values of the crude reaction mixtures produced when the color development was carried out on three samples of pure tocopherols were determined with the Coleman spectrophotometer; they arc pres sented graphically in Figure 1. The spectral absorption valueof an authentic sample (18) of the chroman-5,6-quinone (tocopherol red) formed from a-tocopherol by oxidation in alcohol with nitric acid is given for comparison. On the basis of a previous comparison of results obtained with this instrument and those obtained with the Beckman spectrophotometer (18), the value 1.27 cm. w&s used as the cell length in the Lambert-Beer equation to calculate from the measured optical densities. The identical position of the maximum and the great'similarity in shape of the spectral absorption curves for tocopherol red and the oxidation product of y-tocopherol is very strong evidence that y-tocopherol is converted to tocopherol red by oxidation with nitric acid in acetic acid solution. Furthermore the heights of the maxima indicate that 96% of the y-tocopherol was converted to tocopherol red at room temperature in about 30 seconds.
1 C a and Cy are the concentration of a- and y-tocopherol expressed in grams per 100 ml., L490and L420 are the usual L values determined with the Evelyn colorimeter using the filter indicated by the superscript and using the acetic acid-chloroform solution of the sample &s the blank, and the K's are specific L values determined from known mixtures of pure a- and y-tocopherol. In oils, the percentage of y-tocopherol equals 10 X Cy divided by the weight of the sample in grams. Similar equations can be written for mixtures involving @-tocopherol. REMOVAL OF INTERFERING SUBSTANCES. Two types of interference may be observed in highly pigmented oils and concentrates; one is the result of bleaching certain pigments, such as carotene, by the nitric acid, thus making it impossible to prepare a suitable blank; and the other results from the development of yellow to red colors by the action of nitric acid on extraneous substances originally either colored or colorless. The Parker-McFarlane (11) treatment of oils prior to treab ment with nitric acid has been found very satisfactory for removal of both types of interfering substances. I n the ParkerNcFarlane procedure as applied here, 1 to 2 grams of the oil are weighed into a 100-ml. oil-centrifuge tube and dissolved by the addition of 80 ml. of purified Skellysolve B. Ten to 20 ml. of sulfuric acid (8570 by weight) are added to the solution, and the tube is stoppered with a cork coated with sodium silicate to protect i t from attack by the sulfuric acid. After the tube is inverted several times to assure adequate contact between the sulfuric acid and the Skellysolve B solution, the mixture is centrifuged (ca. 5 minutes a t 1500 r.p.m.) to separate the brown
225
I
1
I
I
I
I
1
T-TOCOPHEROL+ ti
2215.0
w I-
z k!
0 LL
& 10.0 0 0
z
0
I-
o 2
5
5.0
w
I
0.0 380 Figure 1.
~
a-TOCOPHEROL
~~
460 4 8 0 500 5 2 0 400 4I20 . 4 4 0 WAVELENGTH, MILLIMICRONS
Spectral Absorption pf Oxidation Products of a-,8-, and y-Tocopherol and Tocopherol Red
226
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 17, No. 4
DETERMINATION OF ~-TOCOPHBBOL CONTENTOF VEGETABLE OILS. Thirteen samples of oila representing 7 different oilseeds were analyzed for ytocopherol, In addition, the recovery of ytocopherol waa checked by adding i t t o one of the oils and also by adding both a- and -,-tocopherol to a cottonseed oil from which all but 0.008% of tocopherol had been removed by adsorption on carbon and alumina (18). The results of these determinations are given in Table 111. Duplicate determinations were made in Table II. Percentage of 7-Tocopherol Found in Known Mixtures d a- and -pTocophrrol all c a e s . Of the oils examined, only crude cottonseed oil, rice bran oils, a-Toco hero1 ?-Tocopherol Ad&d Added Found Difference Found and okra seed oil required treatment by the Parker-McFarlane MU. Mg. M9. MR. % method for the removal of interfering substances. 2.26 0.49 0.47 -0.02 96 0.00 100 0.97 0.21 0.21 The ytocopherol contents of the soybean oils, crude peanut 1.43 1.04 1.10 f0.06 106 4.83 0.52 0.65 t0.03 106 oil 1, and refined cottonseed oil 2 were determined both with and 0.28 1.79 1.80 +0.01 101 without prior treatment by the Parker-McFarlane method., The 2.02 0.93 O.Q2 -0.01 99 3.80° 0.77 0.74 -0.03 96 agreement in the values found with the treated and untreated 1.10 gram of eanut oil freed from tocopherol by molecular distillation oils indicates that tocopherol is not destroyed by the Parkerand chromstograp%a adsorption were also added. McFarlane treatment. Several of the oils were saponified, and the 7-tocopherol content of the unsaponifiable matter waa determined. The values so obtained are compared in Table IV with those obtained on the On the other hand, the dissimilarity of the spectral absorption of oil. the oxidation product of crtocopherol, and the complete absence The agreement between the values determined with and withof any extinction maximum in the region 460 to 480 m p indicates out prior saponification indicates that there is no oxidation of the that none of the a-tocopherol was converted to tocopherol red tocopherol during saponification and that the pyrogallol is reunder these conditions. Exact determination of the spectral moved during washing of the unsaponifiable material. Hence absorption of the reddish-violet product from @-tocopherol was this procedure may be considered satisfactory for the determinadifficult, owing to the rapid fading of the developed color. RELATION BETWEEN INTENSITY OF COLORAND TOCOPHEROLtion of less than 0.02% of ytocopherol in oils. The lowest value that can be determined will be governed to a large extent by the CONCBNTBATION. I n order to establish the proportionality beamount of interfering material which cannot be removed by the tween the intensity of the color developed by the oxidation of aParker-McFarlane procedure. and 7-tocopherol and the concentration of the tocopherol, several DETERMINATION OF TOTAL AND TOCOPHEROL CONTENT or’ samples of each of these substances were treated as described VEGETABLEOILS. The total tocopherol content of the vegetable above, and the L values determined. The results are shown oils being investigated was determined by a modification of the graphically in Figure 2. There is a linear relation between the L Emmerie-Engel (4)method, which includes the Parker-McFarvalue and the concentration of tocopherol over the range of conlane treatment. The a-tocopherol content was then calculated centration covered for both tocopherols and both filters. DETERMINATION OF CONSTANTS FOR TOCOPHEROL MIXTURES. by difference. Total and a-tocopherol content of the various oils studied are given in Table 111. Since the method is t o be applied t o mixtures, the constants in the equations given above were determined by use of two known mixtures of a- and y-tocopherol. The value of L 4 W was determined exactly 30 seconds after the addition of nitric acid, and I I I Ithe value of L4*0waa determined exactly 30 seconds later. The 0.4 values were nearly constant a t this time but showed a gradual increme on longer standing, particularly when oil wm present. The values of the various constants obtained in this way for a- and 7-tooopherol, as well as those obtained in a similar manner for 8-tocopherol, ace given in Table I. f- T FILTER 4 2 0 0.3 When @-tocopherol is present it is essential that the values be read a t exactly the times indicated, since the color fades rapidly after 30 to 60 seconds. This marked fading is a qualitative indication of the presence of @-tocopherolin samples of unknown w composition. 2 -I RECOVEBY OF -,-TOCOPHEROL IN KNOWN MIXTURES. In order 0.2 to check the accuracy of the method and of the constants, several -I known mixtures of a- and 7-tocopherol covering a wide range of concentrations were prepared, and the -ptocopherol content was 7 aFlLTER420 determined aa described above. The results are given in Table 11. As indicated in this table, the amounts of added 7-tocopherol which were detected by this method ranged from 96 to 106%. 0.I Since the -ptocopherol samples were weighed only t o +0.01 mg. ,--Q FILTER 490 (total weight, 0.20 to 2.00 mg.), this deviation does not seem unreasonable. The relatively good agreement between the amounts of 7-tocopherol taken and found also serves as a proof of the validity of the constants given in Table I. I n working with 0.0 natural products this accuracy may be decreased by the presence 1 I .o 2.0 3.0 4 .O of small amounts of &tocopherol or chromogens not removed by TOCOPHEROL CONCENTRATION ( m p / l O m l . ) saponification or by the Parker-McFarlane treatment. As shown by the last entry in Table 11, as much as 1 gram of oil does not inFigure 2. Relationship of Concentration of a-and y-Tocophterfere with the dekermination. erol to L Value of Solution after Oxidation with Nitric A c i d
Table I. Constants for Determination of 8- or -,-Tocopherol by Means of the Evelyn Colorimeter and Standard Filter Glasses Tocopherol KO0 K4lO Alpha 4.13 1.15 8.6 13.1 Beta 24.4 Gamma 31.5
2
--
ANALYTICAL EDITION
Apd, 1945
227 ACKNOWLEDGMENTS
Table Ill. Toiopherol Content ef Vegetable Oils Tocopherol Content Total y a
%
%
%
Cottonseed oil 1 refined 0.095 0,024 0.071 Cottonseed oil 2: crude 0,110 0.034 0.078 Cottonseed oil 2. refined 0.087 0.037 0.060 Peanut oil 1, crude 0.036 0.018 0.018 Peanut oil 2 , crude 0.052 0.022 0.030 Peanut, oil 3, refined 0.048 0.024 0.024 Corn oil 1. refined 0.090 0.081 0.009 Soybean oil 1. refined 0.099 0.078 0.021 Soybean oil 2 refined 0.094 0.074 0.020 Pecan oil l,,r;fined 0.042 0.022 0.020 Rice bran oil 1 , crude 0.101 0.026 0.075 Rice bran oil 1, refined 0.091 0.033 0.058 Okra seed oil 1, crude 0.074 0.043 0.031 Cottonseed oil 1 0 . 0 2 3 % 7-tocopherol 0.046 . Oil tocopherols’ o:ioi 0.045 o:ob Cottonseed oil 1 freed from tocopherol by adsorption, +0.050% of or-tocopherol and 0.050% of y-tocopherol.
+
+
IV.
Recovery of 7-Tocopherol from Vegetable Oils after. Saponification y-Tocopherol Content of Oil as Determined on: Unsa oniBa&e Oil material Recovery % % % Cottonseed oil 1 , refined 0.024 0.024 100 0.027 0.028 98 Cottonseed oil 2, refined Peanut oil 1, crude 0.018 0.018 100 0,083 102 Corn oil 1, refined 0.081 Soybean oil 1. refined 0.078 0.077 99 Soybean oil 2, refined 0.074 0.081 109 0.023% y-tocopherol 0.048 0.044 96 Cottonseed oil 1 tocopherols“ 0.045 0.045 100 Oil Table
+
+
I, Cottonseed oil 1 freed from tooopherol by adsorption, tocopherol and 0.050% of y-toaopherol.
+ 0.050%
of a-
It is notable that in oil from a given species of oilseed both the a- and 7-tocopherol contents are relatively constant.
There is, however, a wide variation in both the total tocopherol content and the ratio of a-tocopherol to 7-tocopherol in oils from different species of oilseed. Since the tocopherols are antioxidants and 7-tocopherol is about 3 times as active as a-tocopherol, it might be expected that the oils having the highest content of 7-tocopherol would be the most stable. However, refined soybean and. corn oils, which contain about 0.08% of 7-tocopherol, are in general less resistant to oxidation than refined peanut oil, which contains only about 0.02% of 7-tocopherol. It is apparent that the stability to oxidative rancidity of refined vegetable oik in general cannot be predicted solely on the basis of their content of a- and 7-tocopherol. Other factors, such as degree of unsaturation, must be considered, SUMMARY
It has been demonstrcted that 8- and 7-tocopherols form red compounds when treated with nitric acid in acetic acid solution, whereas a-tocopherol does not. The red compound from 7tocopherol has been shsnn to have spectral absorption indicating its identity with tocophcrol red. A colorimetric method of analysis has been developed for y-tocopherol in the presence of a-tocopherol by application of the principle of differential spectral sepa ration after nitric acid oxidation, and has been used to determine the 7-tocopherol content of 13 samples of vegetable oil. These values and the total tocopherol content as measured by the Emmerie-Engel reaction were used to calculate the a-tocopherol content. The use of this method in its present form presupposes the absence of @-tocopherolin the oil t o be analyzed. If 8-tocopherol is present, the characteristic fading observed when the method is applied to 8-tocopherol will generally indicate its presence, and will vitiate the applicability of the method. However, the method may generally be used in analyzing oils of unknown tocopherol(s) content because, so far as is now known, few natural oils contain 8-tocopherol.
The author wishes t o express his thanks t o Merck & Co. for the generous donation of the ,%tocopherol used in this work, and to R. T. O’Connor of this laboratory for determining the punty of the tocopherols. LITERATURE CITED
(1) Ashley, S. E. Q., IND. ENQ.CHEX., VAL. ED., 11, 72-9 (1939). (2) Baxter, J. G., Robeson, C. D., Taylor, J. D., and Lehman, R. W., J . Am. Chem. SOC.,65,918-24 (1943). (3) Devlin, H.B., and Mattill. H. A,, J . Biol. Chem., 146, 123-30 (1942). (4) Emmerie, A., and Engel, Chr., Rec. trav. chim., 57, 1351-5 (1938). (5) Furter, Ma, and Meyer, R . E., Helv. Chim. Acta, 22, 240-50 (1939). (6) Karrer, P., and Keller, H., Ibid., 21, 1161-9 (1938); 22,253-9, 617-18 (1939). (7) Knudson, H. W., Meloche, V. W., and Juday, D., IND.ENO. CREM.,ANAL. ED., 12,715-18 (1940). (8) Kofler, M., Helv. Chim. A d a , 25, 1469-74 (1942). (9) Moore, T., and To&, J., Biochem. J., 37,No. 4,xiv (1942). (10) Olcott, H.S.,and Emerson, 0. H., J . Am. Chem. SOC.,59,10089 (1937). (11) Parker, W. E., and McFarlane, W. O., Can. J . Rcrrarch, 18B, 405-9 (1940). (12) Quackenbuah, F. W., Gottlieb, H. L., and Steenbock, H., IND. ENQ.CHEM.,33, 1276-8 (1941). (13) Quaife, hl. L.,J . Am. Chem. Soc.. 66,308-9 (1944). (14) Riemenschneider, R. W.,Turer, J., and Ault, W. C., Oil and s o a p , 21, 98-100 (1944). (15) Scudi, J. V., and Bdhs, R. P., J . Biol. Chem., 141, 1-6 (1942). (16) Smith, L. I., Irwin, W. B., and Unmade, H. E., J . Am. Chem. SOC.,61, 2424-9 (1939). (17) Smith, L. I., Spillane, L. J., and Kolthoff, I. M., Ibid., 64,44741 (1942). (18) Swift, C. E., Mann, G. E., and Fisher, G . S., Oil and Soap, in
press.
(19) Twyman, F.,and Allsop, C. B., “Practice of Absorption Spectrophotometry with Hilger Instruments”, 2nd ed., pp. 414, London, Adam Hilger, 1934. (20) Wiegert, F., Ber., 49, 1496-1532, particularly 1525-32 (1916).
N e w Standard Samples Issued by the National Bureau of Standards The National Bureau of Standards has added new standard samples of potassium dichromate, boron steel, cobaltrmolybdenumtungsten steel, and titanium dioxide to ita list. Boron steel No. 151 contains 0.0027% boron. The composition of the cobalt-molybdenum steel is: carbon 0.86, cobalt 8.5, molybdenum 8.3, tungsten 1.5, chromium 4.1, vanadium 2.0. Standard potassium dichromate No. 136 is issued as an oxidimetrio standard, and standard titanium oxide No. 154 as a standard in colorimetry and oxidimetry. Standard boron steel No. 151 is priced at $2 per 150 grams: standard Co-Mo-W Steel No. 153,at $3 per 150 grams; standard KsCrrOl No. 136,at $4 per 75 grams; and standard TiOt,$2 per 40 grams. The bureau now issues more than 150 different kinds of standard samples, comprising steels, irom, ferroalloys, nonferrous alloys, ores, ceramic materials, certain high-purity chemicals, hydrocarbons, and melting-point standards. A complete list of the standards, fees, and other information is given in the Supplement to Circular 398, which can be obtained free of charge upon application to the National Bureau of Standards, Washington 25. D. C.
Collective Index, Analytical Edition The fifteen-year collective index to the ANALYTICAL EDITIONof ENGINEERIXG CHEMISTRY has been printed. All copies ordered at special prepublication price have bean mailed. This index should prove invaluable to all analytical chemists. A low price ($2.25)has been set to encourage wide distribution. IhPlJslTLIAL AND
