INDUSTRIAL A N D ENGINEERING CHEMISTRY
948
TABLEI. SALTCONTENT OF CRUDE (Pounds of S a C l per 1000 barrels of crude. method.) A B C D r y O P O P O P O P 7 4 77 73 76 54 59 65 67 70 72 65 67 54 53 60 62 68 70 74 7 4 48 53 53 63 73 79 72 76 58 51 49 67 5 .. 67 . . 65 51 .. 63 Av. 71 73 71 72 54 53 57 64
Lrtborat o 1 2 3 4
..
0, own method. O 118 109 116 107
...
113
E
P 114 110 109 117 109 112
O 77 79 64 62
F
P , proposed P O 79 73 77 70 78 78 76 68
. . . . ..
71
78 72
G
P 76 73 72 74 68 73
coagulate the soap and prevent a pink coloration. When the soap was added to the standard potassium chloride solution, followed by the zinc acetate, and adjustment to the litmus end point, titration gave a ratio of 0,999 to 1.
Experimental The adaption of the tetraethyllead extraction apparatus to the determination of the salt content of crude oil is obvious, and requires no detailed description. The balance of the work consisted of a n exchange of samples between five laboratories of this company. Each laboratory was asked to supply samples of crude representative of the general run handled, choosing as troublesome samples as possible. Seven samples n-ere circulated, and were analyzed both by the procedure then in use a t each laboratory and by the proposed method. Table I gives the results. The proposed method was new to the operators. The reproducibility may be expected to improve with practice.
Vol. 14, No. 12
The time required for the proposed method is longer, for one sample, than that required for the other methods studied. The other methods, however, require constant activity on the part of the operator, while with the proposed method, the extraction is made without attention. With three sets of apparatus, one operator can analyze three samples every 45 minutes. Duplicate determinations by one operator check to within 2 pounds of sodium chloride per thousand barrels of crude oil. The variations shown in Table I are considerably larger than this, but inexperience with the method and difficulties in sampling prevent an exact evaluation of the reproducibility.
Acknowledgment The authors wish to thank the personnel of the other laboratories for their cooperation in the preparation and analysis of the crude oil samples.
Literature Cited (1) A. S. T. M. Designation D52641T. (1) (2) Blair, C. M., Jr., IND.ENQ.CHEM., CHEM.,ANIL. ED.,10, 207 (1938). (3) Horne, J. W., and Christianson, L. F., U . S . BUT.Mines Rept.
3517 11940).
Scott, “Standard Methods of Chemical Analysis”, 6th ed., Vol. I, p. 272, D. Van Nostrand Co., New York, 1939. ( 5 ) Universal Oil Products Co., “Laboratory Test Methods for Petroleum and Its Products”, Procedure A-3, 1940. (4)
PRESENTED before the Division of Petroleum Chemistry at the 102nd CHEMICAL SOCIETY, Atlantic City, N. J. Meeting of the AMERICAN
Colorimetric Determination of Vitamin C 3x. L. ISAACS DeLamar Institute of Public Health, Columbia University, New York, N. Y.
V
ITAMIY C as a moderately strong reducing agent is
capable of producing colored reduction products from a number of the phospho- and silico- molybdates and tungstates. One of these reactions has been adapted by Brand and Kassell to a quantitative determination of the vitamin ( 1 ) . Another, which offers certain advantages under suitable conditions, is the reaction between vitamin C and silicomolybdie acid produced by the reaction of ammonium molybdate and sodium silicate in acid solution. The reaction is sensitive, 0.01 mg. of the vitamin in 50 ml. of solution producing a discernible color; the reagent is stable and can be kept for long periods; and the blue reduction product is not reoxidized by exposure to air. I n the procedure described below, using the photoelectric colorimeter, natural coloring matter in the yellow and red part of the spectrum does not interfere with the test. The method described is suitable for determining the vitamin C content of fruits, vegetables, and other materials in which the content of other reducing substances is low-e. g., bananas and lemon juice. In other materials it gives results more nearly comparable to the iodine titration and therefore tends to run higher than the indophenol method. The molybdate reagent is easily reduced by ferrous and stannous ions and more slowly by cysteine, sulfites, and thiosulfates. PREPARATIOX OF REAGENT. Two grams of ammonium molybdate are dissolved in 50 ml. of water at about 55’ C., and 10 ml. of 1 per cent sodium silicate solution (Na&3iOa.9Hz0) freshly prepared are added, followed by 5 ml. of glacial acetic acid. The volume of the solution is then made up to 100 ml. After standing overnight the reagent is ready for use. The reagent keeps indefinitely. After several weeks a white
precipitate forms (probably molybdic acid) but the loss of this material does not interfere with the use of the reagent. PROCEDURE. An extract of the material to be examined is prepared by grinding a weighed quantity with 5 per cent acetic acid and sand in a mortar. After filtration and washing of the residue with fresh 5 per cent acetic acid, the filtrate is made up to a suitable volume. An extract of this type is stable for approximately 3 or 4 hours. If kept overnight, even in a refrigerator, loss of vitamin may run as high as 10 per cent. With some materials, such as bananas, extraction may be made directly with a measured quantity of diluted reagent and sand. In making a determination, a suitable quantity of filtrate containing up to 1 mg. of vitamin C is placed in a 50-ml. volumetric flask with approximately 25 ml. of water; 5 ml. of reagent are added, followed by distilled water up to the graduation mark. One milliliter of reagent is sufficient in the range of 0.01 to 0.1 mg. The contents of the flask are thoroughly mixed and allowed to stand for 15 minutes before making a reading. If the solution is turbid it may be filtered. The 50-ml. volume was chosen for convenience in measuring reagents; any smaller volume, however, may be used with proportionate decreases of reagent and dilution water. The depth of color may be estimated in two ways, using standards in Nessler tubes or a photoelectric colorimeter, the latter method being preferred. The Duboscq colorimeter is not suitable in this procedure because of the presence in the final product of varying amounts of excess of the yellow reagent. For the preparation of standards in Nessler tubes, solutions of pure ascorbic acid may be used. The convenient range contains 0.01 to 1 mg. per 50-ml. h a 1 volume, in steps ranging from 0.01 or 0.02 to 0.2 mg. In this higher range the colors may be matched from the side. The fact that the final color results from the partial disappearance of yellow and the formation of a blue color accentuates the difference between the standards. During the course of 2 days after preparation, the standards tend to increase in color. If at the end of this time they are readjusted with diluted reagent, they remain unchanged for several weeks. Further storage results in a gradual loss of the blue color.
December 15, 1942
949
ANALYTICAL EDITION
For more precise readings a photoelectric colorimeter can be used to great advantage. As in other methods with this type of instrument, a curve of instrument readings against concentration is plotted with known standards and subsequent readings obtained with unknowns are translated into concentration by reference to the curve. The most important problem in the use of the colorimeter is the choice of a proper light filter. The reagent, although yellow in color, transmits practically all of the red end of the spectrum. If, therefore, a red filter is used, the reagent itself gives no reading, while the blue compound, which absorbs red light, is effectively measured by the photoelectric cells. A number of filters, such as the Pyrex No. 241 pyrometer red glass and the Klett Summerson
'
66, have proved satisfactory. Use of red light for absorption has a number of advantages: (1) Certain turbidities such as result when fresh lemon juice is tested, and which cannot be removed by filtration, do not affect the readings, and ( 2 ) , a variety of natural colors are in the yellow or red part of the spectrum and therefore have no appreciable effect on the absorption of the beam of light. The method should prove useful for routine comparative tests in materials free from interfering substances or where such substances are present in quantities that can be ignored.
Literature Cited ( 1 ) Brand, E., and Kassell, B., J . Biol. Chem., 125, 115 (1938).
The Distribution of Cut Fiber Lengths In Wool Sampled by Cylindrical Tube Borings IRVING hIICHELSON AND LOUIS TANNER, u. s. Customs Laboratory, Boston, >Iass., U. S. Treasury Department, Washington, D. C.
Tn
HE sampling of raw wool by the method described by
and Tanner (4) results in the cutting of some fibers of the wool. The distribution of the various resulting lengths of cut fibers is of interest both to the laboratory testing the wool samples and to the manufacturer using the wool. The presence of considerable quantities of fiber of very short length in the sample may result in error, since these may be lost in the subsequent analysis. On the other hand, the presence of considerable quantities of short fiber in the bulk of the raw wool may introduce difficulties in certain manufacturing operations. The distribution of cut fiber lengths by physical measurements of staple lengths can be determined by the usual equipment used for such purpose, provided, of course, that the precision of the method is sufficient to reveal the increase in short fibers resulting from sampling. This problem may also be subjected to mathematical analysis. The mathematical treatment presented herein attempts to determine the average distribution of cut fiber lengths when the fiber cutting incident to sampling is a t a maximum. While this calculation of cut fiber lengths is made with particular reference to the sampling method described (C), it may also be useful in other sampling or cutting problems of similar nature. The sampling method consists of drawing a cylindrical core of wool from a bale by means of a rotating sharp-edged circular tube. Figure 1 shows such a tube partly thrust into a bale, ABDC outlining the core which would be withdrawn. The fibers which are cut are those lying in the path of the cutting edge. Part of the cut fibers is in the core of wool in the sampling tube: the balance is left in the bale. Formulas for determining the quantities of cut fibers both inside and outside the tube, and tables of weights and percentages calculated from these formulas, are given below. The I derivations of the equations are B W . presented following the tables. The formulas deal only with the short fibers resulting from the sample cutting operation, and not FIGURE 1 0llner
@
AND
H. J. WOLLNER,
with such quantities of short fibers as may already be present through double cutting in the original shearing of the wool. Equations 1 and 2 express the bulk volume of cut fibers of length IC or less in terms of practical physical factors which can be determined easily. These factors are the average original fiber length, the sampling tube diameter, and the depth of penetration of the tube into the bale. These equations represent the average effect of maximum cutting. Remaining in the bale (outside the sampling tube) : dpk2
J7 = -
f
I n the core sample (inside the sampling tube) : Ti
=
k p l / d 2 - k2 (k/f
-
d2p + r360 arc sin ( k ; d )
(2)
n here V
= volume of cut fibers of length k or lei% k = any given cut fiber length d = diameter of sampling tube p = depth of penetration of tube into bale .f = average original fiber length Arc sin ( k / d ) is expressed in degrees.
FIGURE 2
A formula for the weight of cut fibers of length k or less remaining in the bale is obtained by multiplying Equation 1 by the density of the bale, D. Weight
dpk2D
=-
f
(3)
