Iodine Value.of Tung Oil Effect of Time, Excess of Wijs Reagent, and Temperature K. Ho,C. S. WAN, AND S. H. WEN Chemical Research Laboratory, Hankow Bureau of Inspection and Testing of Commercial Commodities, Hankow, China
I
T I S well known that iodine POTASSIUM DICHROMATE SOLUAs a result of research o n the quantitative TION. Dissolve 3.8635 grams of values determined by differrelations of time, excess of W i j s reagent, and c. P. potassium dichromate inwater ent methods do not agree. and dilute to 1 liter. One cubic of tung oil, it was temperature to the iodine value Each method has its own merits c e n t i m e t e r of this solution is found that even after 12 days of contact the iodine and drawbacks. The authors equivalent to 1cg. of iodine, STARCH SOLUTION.Dissolve 1 have been using the Wijs method value tends to increase. It is proportional to gram of soluble starch in 100 cc. in their laboratory and have anathe excess of iodine in centigrams of equivalent of boiling water. lyzed about 5000 samples of tung CHLOROFORM. Use pure dry iodine per gram of oil, instead of being proporoil during the past 5 years. They chloroform. tional to the percentage excess of W i j s solution, 0.1 N SODIUM THIOSULFATE Sohave noticed that the ratio of LUTION. Dissolve 24.82 grams of as usually stated. Wijs solution to the weight of pure sodium thiosulfate (Na& oil, the length of time of contact, I f the ratio of W i j s solution added and weight 03.5H20) in water and dilute to 1 and the temperature all affect liter. Let it stand for one month, of sample of oil is kept constant, almost identical filter, and standardize by the the iodine d u e . A slight change iodine ualues are obtained when temperature Volhard method. in any of the above items will and time are the same. W h e n time of contact cause an appreciable difference GENERALPROCEDURE and excess of iodine are constant, the iodine in the iodine value. Weigh by difference 0.13 to 0.23 Up to the present there is no value increases with increase in temperature. gram of oil and put in a 300-CO. standard specification for the W i t h the same excess of W i j s solution, almost iodine flask, add 10 cc. of pure Wijs method. The specifications chloroform and then a certain identical iodine values can be obtained at different given by different authorities amount of Wijs solution. Place of contact. temperatures by varying time the flask in a thermostat for are tabulated in Table I for comdefinite length of time and, after Standard conditions for converting iodine parison. the flask is taken out, add 10 It is not only impossible to value are proposed. cc. of 15 per cent potassium iocheck the iodine value obtained dide solution and 50 cc. of water and titrate with 0.1 N sodium by the Wiis method according to specifications of two different authorities, but also im- thiosulfate solution, using 1 per cent starch solution as indicator. The iodine value is expressed as centigrams of equivalent iodine possible to check the results obtained with the same speci- absorbed by 1 gram of oil. fication, as variations within the limits are enough to cause an appreciable difference in iodine value. EFFECT OF TIME The Wijs solution used by the authors contains about 2.6 SPECIFICAT~ONS FOR DETERMINATION OF IODINE cg. of equivalent iodine per cubic centimeter of solution, and VALUEGIVENBY DIFFERENTAUTHOR~TIES 25 cc. of Wijs solution is used for every 0.175 gram of oil. CONCEA-TRATION OF WEIQHT TIMEOF When the weight of oil is not exactly 0.175 gram, the amount WrJa OF TEMPER.4- CONTACT of Wijs solution is adjusted to this ratio. Reagents are kept AUTHORITY SOLUTION* OIL TURE IN DARK Cg. Gram C. Min. a t room temperature, while the length of time of contact Am. Soo. Testing Materials (2) 2 . 6 0.16-0.19 21-23 30 varies from 0.5 hour to 12 days, The data are tabulated in 2.6 . . . . .. . ... 10 Allen (I) 2 to 6 hours Table 11. Lewkowitsch ( 6 ) 2.6 0 15-0.18 TABLEI.
Villavecohia ( 6 ) Assoc.OffioialAgr. Chem. (5) Griffin (4) a
2.6 2.6 2.6
0110-0.20 0.10-0.20 0.10-0.20
l k l i S About 2 hours 30 lhour
TABLE11. EFFECTOF TIMEON IODINE VALUE
20-125
TIMEOF AVERAGE IODINE TIME OF AVERAGE IODINE CONTACT VALUE CONTACT VALUE Hours Days 0.5 166.8 1 180.7 2 171,8 2 183.4 4 173.9 6 192.9 177.3 10 197.0 7 12 199.6
Equivalent iodine per cubic centimeter.
The purpose of this research is to find the quantitative relations of the different factors with the iodine value of tung oil.
The iodine value increases with the increase in time of contact and, a t the end of 12 days, is 199.6. This value is much higher than any given in reference books and will continue to increase if the time of contact is lengthened. It may b e possible to reach a n end, but it takes too long a time.
REAGENTS WIJS SOLUTION.Dissolve 13 grams of pure iodine in 1 liter of glacial acetic acid (Kahlbaum 99 t o 100 per cent) and then pass in chlorine gas, which has been previously dried by passing
through two washing bottles, one containing water and the other containing concentrated sulfuric acid. The addition of chlorine gas is stopped when the halogen content is doubled. This solution must be stored in an ice box during the summer and it is better not to use any solution which has been made up more than one month; otherwise the unstable iodine trichloride will be formed and it is not suitable for determining iodine values ( 5 , 5 ) .
EFFECT OF EXCESS OF IODINE The excess of Wijs solution is usually expressed in percentage. Most reference books state that the iodine value is usually directly proportional to the percentage excess of 96
ANALYTICAL EDITION
March 15, 1935
Wijs solution, but this statement is not strictly true. It is clearly seen in Table I11 that samples 1 to 5 have different ratios of Wijs solution and also different iodine values, though the percentage excess is practically the same. From Table I11 it appears that the iodine value is proportional to the excess of Wijs solution only when the percentage excess is above 39. If we add still less of Wijs solution, the percentage excess will remain around 39, but the iodine value will become considerably lower. If, however, the excess is expressed in centigrams of equivalent iodine per gram of oil, the iodine value will then be proportional (Table IV). TABLE111. EFFECT OF EXCESS OF IODINE ON IODINE VALUE SAMPLEWEIGHT OF No. OIL Gram 0.2153 0.2090 0.2109 0.1985 0.2282 0.1785 0.1844 0.1723
(1 hour at 21.5O C.) RATIOOF WIJS EXCESSOF WIJS SOLUTION TO OIL SOLUTION Cdnram % .. 38.7 ii.ijo.13 37.8 11.8/0.13 37.0 12.5/0.13 37.2 13.7/0.13 38.8 14.4/0.13 45.1 16.4/0.13 54.1 20.0/0.13 64.7 26.5/0.13
IonIh-E VALUE 123.3 133.1 143.4 156.9 160.3 163.6 167.1 170.1
to set up arbitrary conditions and consider the iodine value thus obtained as the standard iodine value, so that it will be possible to compare the results obtained in different laboratories. RELATION OF TIMEAND TEMPERATURE With the same excess of Wijs solution added, it was possible to get almost identical iodine values a t different temperatures by varying the length of time of contact. TABLEVII. EFFECTOF TIMEAND TEMPERATURE AT DEFINITE EXCESS
1 2 3 4 5 6 7 8
(1 hour at 21.5' C.) WEIGHT OF EXCESS OF WIJS IODINE OIL SOLUTION EXCESS OF IODINE VALUE Gram % 123.3 38.7 77.8 0.2153 37.8 80.9 133.1 0,2090 37.0 84.2 143.4 0.2109 37.2 92.9 156.9 0.1985 38.8 101.6 160.3 0.2282 45.1 134.4 163.6 0.1785 54.1 197.0 167.1 0.1844 170.1 64.7 311.8 0.1723
OF IODINE IODINE TEMPERA. EXCESS VALUE TURE IODINE VALUB
TEMPERA- EXCESSOF TURE IODINE
c.
Cg./gram
O
c.
.
Cg /gram BERIEBB. 0 . 6 E O U R
SERIES A. 1HOUR
19.5
203.0 203.2 204.0 203.3
166.0 166.3 165.7 166.0
29.5
202.3 201.8 201.8 201.5
166.0 166.3 166.2 166.5
19.9
204.0 202.9 202.8 202.7
165.2 165.5 166.0 165.4
29.9
200.4 200.4 201.2 200.5
165.6 166.0 165.2 165.6
24.5
202.2 201.6 202.0 201.2
166.8 167.3 167.1 167.5
34.6
198.7 199.0 199.2 198.9
166.9 167.1 167.0 167.0
25.1
209.0 200.7 200.6 201.2
166.4 166.8 166.8 166.7
34.9
198.1 199.1 199.3 198.2
167.0 166.3 166.3 167.6
29.9
198.0 197.7 198.0 198.3
168.6 168.1 168.1 167.7
40.5
195.0 195.9 195.6 194.2
168.1 167.6 167.5 168.3
TABLEIV. RELATION OF EXCESSOF IODINE TO IODINE VALUE SAMPLE No.
97
.
In Table VI1 the results of two series of experiments are tabulated. The excess of iodine for both series is approximately the same, but for series A the reaction temperature is pIf,the Wijs solution added and the weight of oil are kept about 10" lower and the time of contact twice as long. It is a t a'constant ratio, we get practically identical iodine values noteworthy that the iodhe values of the different groups (Tabley), when temperature and time are kept the same. in series A are nearly identical with those of the corresponding groups in series B. It may therefore be assumed that the TABLEV. IODINEVALUEOF OILWITH PROPORTIONAL AMOUNTS reaction velocity is approximately doubled with a temperature OF WIJS SOLUTION increase of 10" C. (Temperature, 21.5O C.) The relation of time and temperature has been worked WEIGHTOF OIL IODINEVALUE WEIQHTOF OIL IODINEVALUE out on this assumption with 1 hour a t 20" C. as the basis @am Gram 1 HOUR 2 HOURB and the result is presented in Table VIII. 0.1343 0.1456 0.1527 0.1642 0.1740 0.1804 0.1910 0.2008 0.2142
167.0 167.1 167.4 167.2 167.2 167.0 167.2 167.1 167.2
0.1398 0.1668 0.1722 0.1850 0.1950 0.2226
174.6 174.9 174.9 174.4 174.4 174.8
EFFECTOF TEMPERATURE We know that both time (Table 11) and excess of iodine (Tables I11 and IV) affect the iodine value. Now we keep the time a t 1 hour and the excess around a definite value and determine the iodine values a t different temperatures. The data presented in Table VI show that the iodine value increases with the increase in temperature. TABLEVI. EFFECTOF TEMPERATURE ON IODINE VALUE TEMPERATURE Excnsa OF IODINE
c.
20.0 26.3 32.0 38.6
Cg./gram 218.8 210.8 223.5 216.6
IODINB VALUE 166.5 167.8 170.1 171.9
From the results obtained above, it is clear that the iodine value given by any laboratory, up to the present, is only an approximate figure obtained under a certain set of conditions which, even in the same laboratory, can never be all kept identical a t different times. It is therefore necessary
TABLEVIII. RELATION OF TIMEAND TEMPERATURE
1
TEMPERATURE REACTION VELOCITYTIMEOF CONTACTVELOCITY TIME
c.
1
2v 4v 8V
..
t
Hours
v
20 30 40 50
'/a
:ji..
..
2
(7) v
2-
Constant
(9)
From this table we see that the time in hours, H, required for a definite temperature equals 2-(%?: t
-20
H = 2-(rO) = 2 log H
(%-'I
- 5og2 10
= 2o
= 0.030103 (20
- t)
(1)
That is, the iodine value obtained by working a t t o C. for a contact of H hours will be approximately the same as that obtained a t 20" C. for 1 hour, when the excess of iodine is the same in both cases. The equivalent time, H, in hours is calculated for various temperatures by Equation 1 with 20" C. and 1 hour as the basis. When H is converted into minutes and plotted as shown in Figure 1, it is easy to read the time of contact necessary for any given temperature.
INDUSTRIAL AND ENGINEERING CHEMISTRY
98
Vol. 7, No. 2
o, le #a yo
/IO
*E ” bm
E m PIX
d,
m 40
rn 20 10
10.
IO’
w
4 6 .
s#
Temperature,‘C.
FIGURE1. RELATION OF TIME AND TEMPERATURE AT DEFINITE EXCESSOF IODINE
V
80
hW
NO
/&
/60
/80
ZG,
120
W
260
280
300
320 340
360 34 4W 420 440
Excess of Iodme@y,yrumoi/l
FIGURE2. IODINEVALUEvs. EXCESSAT DIFFERENT TEMPERATURES
FIGURE4. SLOPEOF LOGCURVEvs. TEMPERATURE
FIGURE 3. LOOIODINEVALUEvs. LOGEXCESSAT DIFFERENT TEMPERATURES In order to verify this relation, a series of experiments has been carried out with temperatures and their corresponding time read off from Figure 1. The iodine values thus obtained turn out to be practically the same (Table IX), and prove the validity of Equation 1.
EFFECTOF TEMPERATURE AND EXCESS OF IODINE
It is easy to adjust the time according to the temperature and obtain identical iodine values, but rather inconvenient to add proportional amounts of Wijs solution to oil samples of different weights. It is desirable to find some definite relation of temperature and excess of iodine with the iodine value, in order to determine the iodine value with certain excess of iodine a t room temperature and convert to any
fixed excess of iodine and fixed temperature chosen as standard. In order to keep the Wijs solution a t the same terpperature, an automatic buret is used in the same thermostat. The oil is weighed by difference into an iodine flask, chloroform Temperuiure,”C. * added, and then placed in the thermostat. FIGURE5. Kt vs. TEMPERATURE After both have attained the temperature of the thermostat, the Wijs solution in the automatic buret is then added to the iodine flask. The flask is taken out after exactly 1 hour and titrated in the usual way. The result is given in Table x. The data in Table X are plotted in Figure 2 with excess of Wijs solution expressed in centigrams of equivalent iodine per gram of oil as abscissa and iodine value as ordinate. From the curves it is clear that the iodine value increases with increase in temperature and with increase in excess of
ANALYTICAL EDITION
March 15, 1935 TABLEIX.
OF EXCESS OF IODINE AND TABLEX. RELATION IODINE VALUEAT DIFFERENT TEMPERATURES
IODINE VALUES AT DIFFERENTTEMPERATURES EQUIVALENT TIMEOF CONTACT
WITH
(1 hour a t 20n C. a# basis) EXCESS OF WIJS E X C E E OF~IODINE TEMPERATURETIME SOLUTION AVERAGEVALUH~ IODINEV A L U ~ Min % Cg./gram O c. 54.92 166.5 74 54.92 203.9 166.3 17.3 54.92 166.4 Av. 54.92 Bv. 166.4 54.88 166.4 59 64.90 203.6 166.5 20.2 54.86 166.4 AT. 54.88 Av. 166.4 54.75 166.8 51 54.79 203.2 166.8 22.3 54.79 166.8 Av. 54.77 Av. 166.8 54.84 166.3 42 54.79 203.1 166.5 25.1 54.86 166.0 Av. 54.83 Av. 166.3 54.57 166.4 36 54.52 201.0 166.6 27.7 54.54 166.5 Av. 54.54 Av. 166.5 54.29 166.9 29 54.39 199.6 166.7 30.4 54.31 166.9 Av. 54 33 Av. 166.8 54.17 166.8 20 54.20 198.3 166.8 36.1 54.13 166.8 Av. 54.17 Av. 166.8
.
I
Ififi.6 .....
54.17 .....
38.0
17
54.07 64.04 64.08 Av. 54.09
167.0 166.8
197.7
166.8
Bv. 166.8
iodine, when the concentration of Wijs solution and the time are kept the same for the different series. Since no general relation can be deduced from Figure 2, the logarithms of all the values are plotted in Figure 3. All six curves then give fairly straight lines for abscissas 2.15 to 2.65. Now, if we let mt be the slope of the line at t o C., theiodine value, Yt, at excess X can be expressed by the following equation:
(Time of contact, 1 hour) CONCN. EXCESS WIJS OF IODINE WIJa OF SOLUTION IODINE VALUE SOLUTION IODINE Cg./cc. Cg./gram Cg./gram Cg./cc. Cg./gram 20.00 c. 32.0' C. 333.4 169.9 124.6 109.7 159.5 386.5 266.8 169.3 297.5 2.549 191.2 165.5 2.532 223.5 160.2 163.6 181.2 127.3 161.9 154.2 144.6 97.5 155.5 391.5 114.7 160.1 279.6 168.2 164.2 211.2 2.548 218.8 166.5 2.530 181.0 270.0 169.0 154.1 111.2 350.0 171.3 428.0 172.4 142.0 26.3' C. 35.6' C. 400.1 174.4 403.0 281.6 171.1 298.7 169.0 165.2 236.0 2.546 146.3 163.8 2.524 179.4 128.1 162.2 103.8 102.5 158.8 120.8 154.7 350.4 172.4 375.5 266.5 170.5 263.0 208.3 167.2 211.5 2.544 183.7 167.0 2.523 94.9 142.5 163.8 122.6 117.6 161.4 148.7 210.8 167.8 29.20 c. 38.6O C. 175.0 357.2 363.0 172.3 98.3 289.8 159.5 267.0 104.3 169.0 2.516 195.4 221.0 2.537 165.4 161.4 158.3 160.9 136.7 111.7 166.2 112.5 169.2 176.4 408.0 371.6 173.3 318.8 276.8 171.8 273.4 216.6 2.516 202.3 168.0 177.7 2.600 121.5 162.4 99.0 166.1 116.7 166.6 162.2 120.2 147.0 CONCN.
EXCESB
...
where
Am =
...
162.7 176.9 173.1 170.1 167.6 165.5 164.8 177.0 172.0 168.7 167.0 166.1 160.6 165.2 179.5 176.0 173.1 169.0 159.7 163.5 167.3 178.7 173.6 170.3 156.0 163.1 166.3
...
179.9 167.4 175.7 170.8 168.2 165.5 162.2 180.3 176.8 171.9 169.6 158.5 162.8 167.2
TABLEXI. RELATION OF SLOPEAND TEMPERATURE SLOPE TBMPERATURE
c.
rn =
ti2
-
v1/m
- It
2.23770 - 2.21215 -0 = o,05110 2.65 - 2.15 2.24486 - 2.21404 - 0.03082 = o.06164 2.65 - 2.15 0.50 2.24847 - 2.21523 0.03324 - o.06648 2.65 - 2.15 0.60 2.25221 - 2.21663 0.03558 = o.07116 0.50 2.65 2.15 2.23746 - 2.21887 - 0.03859 = o,07718 0.50 2.65 - 2.15 2.26232 - 2.22122 - 0.04110 o.08220 2.65 - 2.15 0.50
20.0 26.3
-
29.2
-
32.0 35.6
= o.oo1672,"
VALUE
...
+
- ?% - ml -0.08220 - 0.05110 = 0.03110 tn - tl 38.6 - 20.0 18.6
IODINE Cg./gram
...
...
log Y t = mt (log X - 2.15) Kt (2) where Y t = iodine value at t o C. X = excess in centigrams of equivalent iodine per gram of oil K t = logarithm of iodine value at t o C. and excess of 2.15
In order to solve Equation 2 we must know definitely the relation between the slope and the temperature. Let us read off in Figure 3 the slopes of the different lines and tabulate in Table XI. The slope is then plotted against the temperature in Figure 4. It is apparent that
99
38.6
~~~~~
TABLEXII. RELATION OF Kt AND TEMPERATURE (1) TEMPERATURE
(at the point where logarithm KI of excess
c. 20.0 26.3 29.2 32.0 35.6 38.6
c.
increment of slope against temperature
-
2.15)
2.21215 2.21523 2.21404 2.21663 2.21887 2.22122
TABLE XIII. RELATION OF Kt AND TEMPERATURE (2) Therefore,
+ +
0.001672 t 0.01766 = 0.001672 (t 10.56)
mt =
TEMPERATURE O
(3)
Let us go a step further and find out the relation of Kt to the temperature in Equation 2. Read off from Figure 3 and tabulate the results in Table XII. The values in Table XI1 are then plotted in Figure 5. If we subtract from each a common value, B , we get the re1,ationgiven in Table XIII.
c.
20.0 30.0 40.0
Kt
COMMON VALUE, B
2.21215 2.21560 2.22250
2.20870 2.20870 2.20870 2.20870
.....
..
1
2(?)
X 0.00345
+B
lit-B
0.00345f = 1 % 0.00346) 0.00690 ( = 2 X 0.00345) 0.01380( = 4 X 0.00345)
.....
B ~~
From Table XI11 we see that Kt = 2(%
X 0.00345
+B
2
(9 X 0.00345 )
100
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 7 , No. 2
TABLEXIV. COMPARISON OF EXPERIMENTAL AND CALCULATED TABLEXV. IODINE VALUEAT PROPOSED STANDARD CONDITIONS IODINE VALUES DEVIATION EXCESB OF
TEMPBRATUREIODINE
EXPERIJIENTAL DATA Excess of iodine Iodinevalue
IODINB VALUE
Experimental
Calculated
DIFFERENCB
Cg./gram
20.0
160.2 168.2 19112 218.8 266.8 270.0 333.4 350.0 428.0
163.6 164.2 165.5 166.5 169.3 169.0 169.9 171.3 172.4
164.0 164.4 165.5 166.7 168.4 168.5 170.3 170.7 172.5
0.4 0.2 0 0.2 0.9 0.5 0.4 0.6 0.1
160.2 168.2 191.2 218.8 266.8 270.0 333.4 350.0 428.0
26.3
142.5 146.3 169.0 183.7 208.3 210.8 266.5 281.6 350.4 400.1
163.8 163.8 165.2 167.0 167.2 167.8 170.5 171.1 172.4 174.4
163.8 164.1 165.5 166.4 167.7 167.8 170.2 170.8 173.1 174.5
0 0.3 0.3 0.6 0.5
158.3 166.6 169.2 202.3 221.0 273.4 289.8 318.8 357.2 408.0
165.4 166.1 166.2 168.0 169.0 171.8 172.3 173.3 175.0 176.4
165.4 166.0 166.1 168.1 169.1 171.6 172.2 173.3 174.6 176.1
142.0 144.6 154.1 154.2 181.0 181.3 211.2 223.5 279.6 297.5 386.5 391.5
165.2 164.8 165.1 165.5 167.0 167.6 168.7 170.1 172.0 173.1 176.9 177.0
164.7 164.9 165.7 165.7 167.6 167.6 169.4 170.2 172.9 173.6 176.9 177.1
0.5 0.1 0.6 0.2 0.6 0 0.7 0.1 0.0 0.5
148.7 154.7 179.4 211.5 236.0 263.0 298.7 375.5 403.0
166.3 167.3 169.0 170.3 173.1 173.6 176.0 178.7 179.5
166.2 166.7 168.6 170.8 172.2 173.7 175.4 178.6 179.5
0.1 0.6 0.4 0.5 0.9 0.1 0.6
147.0 161.4 177.7 195.4 216.6 267.0 276.8 363.0 371.6
167.2 168.2 169.6 170.8 171.9 175.7 175.8 179.9 180.3
167.0 168.3 169.6 170.9 172.4 175.4 175.9 179.9 180.2
0.2 0.1 0 0.1 0.5 0.3 0.1 0 0.1
O
c.
29.2
32.0
35.6
38.6
Ce./gram
= 2(%)
20.00
0
0 0.1 0.1 0.1 0.1 0.2 0.1 0
+
2(+)
X 0.0008625
0.4
163.8 163.8 165.2 167.0 167.2 167.8 170.5 171.1 172.4 174.4
167.8 167.5 167.5 168.4 167.3 167.8 168.1 168.1 167.1 167.7
165.4 166.1 166.2 168.0 169.0 171.8 172.3 173.3 175.0 176.4
167.8 167.9 167.9 167.7 167.7 168.0 167.9 167.8 168.2 168.1
-0.4 -0.2 0 -0.2 +0.9 $0.5 -0.4 +0.6 -0.1
0
-0.3 -0.3 $0.6
-0.5 0
$0.3 +0.3 -0.7 -0.1
0 +0.1
+o. 1
-0.1 -0.1 $0.2 +o. 1 0 +0.4 $0.3
32.0'C. 142.0 144.6 154.1 154.2 181.0 181.2 211.2 223.5 279.6 297.5 386.6 391.5
0
0.1
168.3 167.7 167.2 167.6 167.2 167.8 167.1 167.7 166.9 167.3 167.8 167.7
3.0.5 -0.1 -0.6 -0.2 -0.6 0 -0.7 -0.1 -0.9 -0.5 0 -0.1
35.6'C.
0.2 0
148.7 154.7 179.4 211.5 236.0 263.0 298.7 375.6 403.0
167.9 168.4 168.2 167.3 168.7 167.7 168.4 168.0 167.8
$0.1 +0.6
$0.4 -0.5 +0.9 -0.1
4-0.6
$0.2 0
38.13~C. 147.0 161.4 177.7 195.4 216.6 267.0 276.8 363.0 371.6
(4)
+B
167.4 167.6 167.8 167.6 168.7 168.3 167.4 168.4 167.7
29.2'C. 158.3 166.6 169.2 202.3 221.0 273.4 289.8 318.8 357.2 408.0
0.3
168.0 167.7 167.8 167.7 167.3 168.1 167.7 167.8 167.9
Av.
Substituting Equations 3 and 4 in Equation 2, we get log Yt = 0.001672 (t 10.56) (log X - 2.15)
+
163.6 164.2 165.5 166.5 169.3 169.0 169.9 171.3 172.4 26.3OC
X 2-*X 0.00345
= 2 ( k ) X 0.0008625
FROM
AVERAQB
c.
142.5 146.3 169.0 183.7 208.3 210.8 266.5 281.6 350.4 400.1
0.3 0.3 0.7 0.1
+B +B
CALCULATED
IODINE VALUEQ
a
+0.2 -0.1 0
-0.1
-0.5 4-0.3 -0.1 0
$0.1
167.8
20° C., 250 w. excem iodine per gram of oil, l hour.
(5)
By using Equation 5 it is possible to calculate the iodine value a t definite excess (logarithm of which is from 2.15 t o 2.65) and temperature (18' to 40' C.) with data obtained a t some other excess and temperature within the same limits as above. The time of contact is fixed a t 1 hour. In utilizing Equation 5 , B is first calculated by substituting the experimental data in their respective places. The value of B thus obtained is used in the original equation to calculate the iodine value a t some desired temperature and excess within limits. The value of B , though slightly different for tung oils having different iodine values, always remains the same for the same sample of oil under different temperatures and excess. B is calculated by Equation 5 for each iodine value de-
termination in Table X. Among the values thus obtained, there are slight deviations due to inherent experimental errors, but the average is 2.20870, which checks with the deduced value in Table XIII. Using this average value of B , the iodine values a t the experimental conditions are then calculated by Equation 5 and tabulated together with the experimental iodine values in Table XIV. A glance at Table XIV will show that the iodine values obtained from experiments and the corresponding calculated iodine values check rather closely except in a few cases. The deviation in each of those cases is still within 1. With the help of Equation 5, the iodine value determined under the conditions of any laboratory can be converted to the conditions of other laboratories for comparison. But
A.NALYT I C A L E D I T I O N
March 15, 1935
it is desirable for all laboratories to state their iodine values converted to a common set of standard conditions, so that all the results will be uniform and readily comparable without further calculation. The authors therefore propose the following specifications:
5. With the same excess of Wijs solution, it is possible to get almost identical iodine values a t different temperatures by varying the time of contact according to the following relation : log H (in hours) = 0.030103 (20 - t )
Concentration of Wijs solution, 2.5 t o 2.6 cg. of equivalent iodine per cc. Excess of iodine, 250 cg. of equivalent iodine per gram of oil. Temperature, 20” C. Time of contact in the dark, 1 hour. Reagents as given under Reagents above.
6. The following formula is given for converting, within limits, the iodine value to desired conditions with experimental data obtained under laboratory conditions:
Under the proposed conditions, Equation 5 will assume the following form :
log Yt = 0.001672 (t
+ 10.56) (log X - 2.15) + 2(&)
X
0.0008625
+B
log Y (under proposed standard conditions)
7. The following conditions are proposed as standard for converting iodine value :
+ 10.56) (log X - 2.15) + 2“) X 0.0008625 + B = 0.001672 (20 + 10.56) (log 250 - 2.15) + 2(%) X 0.0008625 + B = 0.001672 (20 + 10.56) (2.39794 - 2.15) + 2’ X 0.0008625 + B
Concentration of Wijs solution, 2.5 to 2.6 cg. of equivalent iodine oer cc. Excess of iodine, 250 cg. of equivalent iodine per gram of oil. Temperature, 20’ C. Time of contact in the dark, 1 hour. Reagents as given under Reagents above.
=
0.001672 (t
+
+
0.001672 (30.56) (0.24794) 4 X 0.0008625 B B (6) The individual values of B are separately calculated by substituting the experimental data in Equation 5 . The iodine values under the proposed conditions are then calculated by Equation 6, using thkse individual values of B. The resul& are tabulated in Table XV. The iodine values obtained a t different temperatures with different amounts of excess of iodine may have a difference of more than 15 in extreme cases, as shown in Table XV. If, however, they are converted to 20’ C., 250 cg. excess of iodine, and contact of 1 hour, they give almost the same figure. It is interesting to note that the average value thus obtained is 167.8 and the greatest deviation is only *0.9. =
= 0.0161
“
101
+
CONCLUSIONS 1. Even after 12 days of contact, the iodine value of tung oil still tends to increase. 2. The iodine value of tung Oil is proPortiona1 to the excess of iodine in centigrams of equivalent iodine per gram of oil instead of being proportional to the percentage excess of Wijs solution, as usually stated. 3. If the ratio of wijs sOhtiOn added and the weight of sample of oil is kept constant, almost identical iodine values are obtained when temperature and time are kept the same. Of iodine are both 4’ When the time Of ‘Ontact and kept constant, iodine value increases with the jncrease in temperature.
8. The following simplified formula is given for converting the iodine value of tung oil to the proposed standard conditions : log Y = 0.0161 B
+
ACRNOWLEDGNENT The authors desire to express their gratitude to c. y. Wang, Commissioner of the Bureau, for his continuous encouragement and to E. K. Ma0 and H. LiU, chemists of the same laboratory, for their valuable Suggestions and helpful criticisms.
LITERATURE CITED (1) Allen’s Commercial Organic Analysis, 5th ed., Vol. 11, pp. 35-6, (1926). (2) Am. Soc. Testing Materials, Tentative Standards, pp. 247, 249, 251 (1930). (3) Assoc. Official Agr. Chem., Official and Tentative Methods, 3rd ed., pp. 320-1 (1930). (4) Griffin, R. c. “Technical Methods of Analysis,” 2nd ed., pp. 258,310, New York, McGraw-Hill Book Co., 1927. (5) Lewkowitsch and Warburton, “Chemical Technology and Analysis of Oils, Fats and Waxes,” 6th ed., Vol. I, pp. 406, 416, London, Macmillan & Co., 1921. (6) Villavecchia, v., “Treatise on Applied Analytical Chemistry,” Vol. I, pp. 380-1, Philadelphia, P. Blakiston’s Son & Co., 1918. RBCEIVED October 27, 1931. Published with the permission of C. Y.Wang, Commissioner of Hankow Bureau of Inspection and Testing of Commerioal Commoditiea. Ministry of Industries, China.
Courtesy, Universal Oil Products Co.
CRACKING UNIT
