680
ANALYTICAL CHEMISTRY
The results of the iodine number determinat,ions are given in Table I, which lists the means of the triplicate iodine numbers determined by the two methods and the differences between them. There is no difference between the means of the methods. I n s3me individual samples the difference is relatively large but a st'atistical analysis of all the results showed t,hat these differences are not significant. The reduction in the volume of Wijs solution did not, affect the accuracy of the determinat,ion to any significant extent. The st,andard error of a single mean, based on triplicate determinations, was calculated for each type of oil. I t was the same by both methods for soybean ( *0.7), saffloiver ( + 0 . 7 ) , and t.he miscellaneous group ( *0.5). For flaxseed by the .4.O.A.C. method it was 1 0 . 9 and by the modified mercuric acetate method *0.8, whereas for sunflower it Tvas *0.7 and * 0.3, respectively. With the volume of Wijs solution reduced to 10 ml. it seemed advisable to determine how far t,his vias above the theoret,ical requirements and how close to the theoretical the volume could be brought without affecting the iodine number. For this purpose composite samples of freshly pressed oil from soybeans, safflower, and flaxseed were used. The iodine number was determined in triplicate on 0,100-gram samples, using varying amounts of Ki js solution. Five-minute absorption periods were used except for oil from flaxseed, where 6 minutes were allowed. From the values obt,ained using 25 ml. of Kijs solution the theoretical volume required for 0.100 gram of each oil was calculated. The results of this experiment are presented graphically in Figure 1. The equations for the lines were calculated from the first five values for flaxseed, six for soybeans, and all for the safflower. The lines have been extended in the graph only as far as these values. The position of 10 ml. of V-ijs solution is indicated on each line by the vert,ical broken line marked X . The line extends well beyond this point in each case, so 10 ml. of Kijs are more than sufficient for the satisfactory determination of iodine numbers. The regression coefficient was calculated in each case and was insignificant,. The lines, for all practical purposes, are parallel to the axis. Inspection of Figure 1 shows that for iodine
numbers of 200 no excess of Kijs solution is present. Consequently when only 10 nil. are used, the weight of sample must be reduced i f the iodine number is over 200. In all but the safflower samples the value of the iodine number decreases when the volume of TTijs solution closely approaches the theoretical volume. Thiq decrease may be partly compensated for by an increased time interval. Khen the smallest volume of Wijs solution 11-as used in the experiment n i t h Aaxseed and the time was increased to 10 minutes, the value of the iodine number \$as increased from 181.5 to 183.7. K i t h soybeans. the increase was from 127.1 to 128.2. SUMMARY AND COR-CLUSIONS
The mercuric acetate method of determining iodine numbers was modified by reduring the volume of Kijs solution and using unstoppered flasks. Comparison n-ith the official Kijs method of the Association of Official Aigricultural Chemists on a large number of samples shon-ed no significant difference between the results obtained. The effect of decreasing amounts of Kijs solution on the value of iodine numbers !vas investigated. K i t h nonconjugated fat's a,nd oils 10 ml. of Wijs solution are sufficient for 0.1-gram samplrs, provided the iodine value is not more than 200. ACKhOWLEDGBIENT
Alcknowledgmentis made to the Adanis Chemical Company for the supply of sulfonated castor oil. LITERATURE CITED
(1) Assoc. Official h g r . Chem., Official and Tentative Methods of
.Inalysis, p. 495 (1945). (2) Hoffman, H. D., and Green, C. E., Oil and Soap. 16, 236 (1939). and Buswell, R. J., IKD. ENG.CHEM?., A N ~ LED., . (3) N o r m , F. Ai.. 15, 258 (1943). (4) Ihid., 16, 417 (1914). (5) Skell, P. S., and Kadlove, S. B., Ihid., 18, 67 (1946). RECEIVED September 17, 1947. Contributlon 139, Division of Chemistry, Science Service, Dominion Department of Agriculture.
New pH Indicator for Titration of Sodium Carbonate Disodium 4,4'-Bis(d-amino-l-naphthyla~o)-2,2'-stilbenedisulfonate JIICH-IEL TAKhS, D e p a r t m e n t of W a t e r Supply, Detroit, Jllich.
'--'
HE dye resuking from t.he coupling of 1 mole of 4,4'-diTaminostilbene-2,2'-disuiionic acid with 2 moles of @-naphthylamine is assigned the formula by Schultz ( 4 ) . hccording to this SO3H
"2
c> I
I
X=N
CH=CH
XH1
SOjH
I
(_7>
'
N=S
p H of 3.8, t,he indicator lends itself advantageously to the titration of 0.2 S and 0.5 S sodium carbonat'e solutions on the one hand, or alternatively, to t'he direct titration of proportiorlate amounts of t,he solid salt. INDICATOR PROPERTIES
a
authority, the dye is known in the color trade as Hessian Purple N extra and Direct Purple. A study of the dye's properties discloses that it may function profitably as a tit'rimetric indicator in the p H region near 4.0. The defects of methyl orange in&cat,or in the acid titration of crtrbonat,es have long been recognized. UP to the present, the remedy has consisted principally in modifying the indicator through the addition of inert dyes like cyanole xylene FF ( 2 ) . Occasionally, bromophenol blue has been substituted for methyl orange in this tit,ration (6). More recently, modified methyl yellow indicator ( I ) has been proposed for this titration. Each indicator Dossesses Deculiar merits and. handled discriminatingly. -_ .provides advantages over the older methyl orange dye. Inasmuch as the sharpest color change of disodium 4,4'-bis(2-amino-l-naphthylaeo)-2,2'-stilbenedisulfonateoccurs a t a
The dye was prepared by the tetraazotization of 9.5 grams (0.025 M ) of 4,4'-diaminostilbene2,2'-disulfonicacid, Eastman Kodak T4614, and coupling with 8.0 grams (0.06 M) of @-naphthylamine,Eastman Kodak 174 (5). The amine was first dissolved in 50 ml. of glacial acetic acid and distilled water was added with stirring to a 100-ml. volume. Coupling was accomplished in this 50% acetic acid solution. The disodium salt was formed by grinding a weighed quantity of the dye in a mortar with the calculated volume of 0.05 Av SOdium hydroxide and diluting to the proper concentration. Two concentrations of the dye were tested for indicator efficiency: 0.5 and 0.1%. Both solutions have a deep red color. Two or 3 drops of the 0.5% solution suffice for every 50-ml. volume titrated. In the case of the 0.1% solution about 10 drops are
n e ~ ~ ~ ' , ' ~ ~ ~ h a~sirupy , ~ ~consistency, ~ ~ ~ ~presenting ~ s e sa minor problem of handling, On this account, most of the titrations reported in this paper were performed with the 0.1% sohtion. The color characteristics of the indicator were tested using sodium dibasic phosphate-citric acid buffers ( 3 ) . These buffer solutions shoxved the alkaline color of the indicator to be a delicate
V O L U M E 20, NO. 7, J U L Y 1 9 4 8
681
Table 1. Titration oC S o d i u m C a r b o n a t e Solutions* Volume of &SO. A".
Na?COa
N~~CO* Taken M1. 10.00 25.00 4n.00
moo
L"
mu-
tion Gram o.1060
n.z6&n
0.2
N M1. in.02
25.03
n.4240 40.00 0 . 2 6 ~ 0 ... 0,6625
...
deviation from mean
M1. 0.01
0.02
Used A". &vistion 0.6 froln mean A'
1x1. ...
iM1.
1O:Oo 26.08
n:Oi
...
0.02
.. ..
.. ..
0.02 40.00 1.06oo .,. ., 40.05 0.03 All v&lues represent average 01 five deterrninationi. 25.00
rhcoJ Found
Gram 0.1062 0.2653 0.4240 0.2650 0.6632 i.0612
~ ~ lion
% fO.lQ +0.11 0 0
+O.I~ +O.II
red The first transition occu~sat a pH of 4,0 with the appearance of a faint color. At a p~ of 3 4 an emphatic and sharp change to purple takes place. This was the end point to which %lltitrations were conducted, The final conversion to n bluish purple takes place new a pH of 3.0.
I n the electrometric standardization of the sulfuric acid six determinations were made on esch solution. Results of determinations on the 0.2 N acid showed au average deviation from the mean of 0.03%; those of determinations on the 0.5 N acid showed an average deviation from the mean of 0.0140/0. The indicator titrations were conducted in Erlenmeyer flasks i resting a on a white background. Five determinations were made on each of 10.00-, 25.00-, and 40.00-ml. volumes of the sodium carbonate solutions. One drop of 0.1% indicator was used for each 10 ml. of solution a t the end point. Titrations were conducted to the first definite purple color. No eolar standard was used; the color response is so good as to render such a standard superfluous, and artificial light or daylight can be used with equal &. *.r t i" r. i. o" n ~" ." ~". I..
Results given in Table I indicate the precision and accuracy obtainable when the new indicator is used. Comparable results were obtained i n 6 series of determinations in whioh samples of solid carbonate were titrated directly. One may conclude t h a t the new indicator is satisfactory for ordinary titrations of sodium cmbonate with sulfuric acid. LITERATURE CITED
EXPERIMENTAL DETAILS
I n t h e experimental work standmd 0.2 N and 0.5 N solutions of sodium carbonate were prepared by dissolving the reagent grade salt in carbon dioxide-free distilled water. Sulfuric acid solutions
honate solutions, with the experimental indicator. Experimental conditions were equalized as far as possible by employing the same burets for the electrometric and the indicator titrations.
(1922). (3) MoIlvaine, T.C.,J . B i d . Chem.,49.183-6(1921). (4) Sehulte, Gustav. "Farbstofftabellen," p. 293, Berlin, Weidmernnsche Buchhandlung. 1929. ( 5 ) Taras, M., ANAL.Cniu., 19,339-41 (1947). (6)Willard. H.H., and Furman. N. H., "Elementary Quantitstive Analysis," p. 115, New York. D. Van Nostrand Co.. 1935. R ~ c m v mJune 13, 1947
Kinematic Viscometer Tube Cleaning Apparatus JAMES MCGLYNN, Socony-Vacuum Laboratories, Technical Seruiee Department, Brooklyn, N . Y . ANY petroleum laboratories, where large numbers of kinematic viscosity determinations are made, are confronted with the problem of cleaning the modified Fenske-Oswald kinematic viscometer tubes. This operation normally, in addition to being time-consuming, requires large volumes of solvent, necessitates a large stock of tubes, and is accompmied by high breakage. This paper describes an apparatus by means of which a number of tubes may he attached to a manifold and solvent circulated through them until the mineral oil has been thoroughly flushed out. From one to eight viscometer tubes can he cleaned in
approximately 5 minutes. I n the author's laboratory this allows twice as many tubes to be washed in unit time. The use of this equipment results in a reduced consumption of solvent for cleaning and cuts down the amount of tube breakage by reducing the required handling. A somewhat similar apparatus has previously been affersd for sale by laboratory supply houses, includiag C. J. Taglisbue Company, Park & Nostrand Aves., Brooklyn, N. Y. The apparatus described in this article may he purchased from the Emil Greiner Co., 1151Sixth Ave., New York, N. Y. APPARATUS
The kinematic viscometer tube cleming apparatus (shown in Figure 1) consists of the following park: Solvent reservoir construeted of sheet brass having a capacity of approximately 3 gallons. G.E. explosionproof motor, 1\20 h.p., 110-volt, 60cycle, I-phase, G.E. catalog No. 5 KH 23 AC 15. Centrifugal pump, capacity 3 gallons per minute, M. L. Oberdorfer Brass Company, Syraeusc, N. Y. Valve manifold far connecting the modified Fenske-Ostwald kinematic viscometer tubes to the system. Pressure relief valve set a t 1pound pressure per square inch. Line filter, Located on the discharge side of the pump. Rack for supporting the viscometer tubes in an inverted position. An amembly drawing of the equipment is shown in Figure 2 (key cocks &s indicated on this drawing are to he preferred to the needle valves shown in Figure 1). PROCEDURE
F i g u r e 1. K i n e m a t i c Visoometer Tube C l e a n i n g Apparatus
The solvent reservoir is charged with a light petroleum solvent. The usual precautions relative to the use of inflammable solvents should he observed. The viscometer tubes, drained of excess oil, are connected to the valve manifold in inverted positions. The large-diameter side arm of the viscometer is connected to the manifold by means of a 2-inch length of thick-walled synthetic rubber tubing, 0.375 inch in inside diameter. The smdlll-diameter side arm of the tube is placed in the opening in the topof the reservoir and supported in the rack provided. The valves are opened
