OCTOBER, 1935
INDUSTRIAL, AND ENGINEERING CHEJIISTRI
on the shell side is used t o exchange heat between two hydrocarbon oils having substantially the same specific heats. The cooler material enters a t 108" and leaves a t 175' F., a t a rate of 270 pounds per minute. The hotter material enters a t 235" and leaves a t 130' F., a t a rate of 195 pounds Der minute. Calculating the number of eauivalent units first on the basis of the hotter liquid: 270
x = - = 1.38, and 100 235 235 195
- 130
- 108
105 = 8 2 . 5 100 -
I
127
On Figure 3 the point (1.38,82.5) corresponds to an equivalent Of more than two but less than three perfect units* 'Omputing similarly on the cooler liquid we are led to the point (0.72. . , 52.5) which corremonds to an eauivalent of nearly two perfect units. Hence in &hisservice this particular exchanger can be considered as slightly superior to two perfect units. The efficiency is roughly 80 per cent. Example 2. Badger (f) gives an illustration in which brine to each other through a of and water pass countercurrent concentric pipes, 2 per cent of the heat being lost by radiation. The water flow is 8890 pounds per hour and the inlet and outlet temperatures 220" and 120; F. The brine flow is
Karaya Gum J
Apparent Viscosity of Its Aqueous Solutions W. E. THRUN, Valparaiso Universitv, .4ND
H. V. FULLER, Valparaiso, Ind. 9
The sparse literature on Karaya gum, which resembles tragacanth and which is finding increasing use, is briefly reviewed. The nature of the gum particles when in aqueous suspension is discussed. The wide variations in the apparent relative yiscosity and the stickiness of its solutions made it desirable to develop the simple apparatus and technic described for the determination of the relative viscosity of these solutions. A n empirical relation between the concentration of the gum and the apparent relative viscosity of the aqueous solutions is given. ARAYA gum (Indian gum, Sterculia w e n s ) has become an important raw material of the cosmetic, food, and other industries. It resembles tragacanth and is sometimes sold under that name. Its chief chemical constituent is the galactan gelose.
1'715
8510 pounds per hour and the inlet and outlet temperature.; 60" and 190" F. The specific heats of water and brine are 1.00 and 0.786. Calculating on the basis of the water side x = 8510
8890
x 0'785 1.00
220 -- 120 = 6 2 , j
= 0.755, and 100 220
-
60
On Figure 3 the point (0.755, 62.5) corresponds to an equivalent of slightly less than three perfect units. Similar calculations on the basis of the brine lead to the point (1.325, 81.3) which again corresponds to slightly less than three perfectunits. H~~~~this heat exchanger, consisting of 140 feet of concentric pipes, is not quite equivalent to three units, while the efficiencyis about 85 per cent.
Literature Cited (1) Badger, "Heat Transfer and Evaporation," 13. 58, New Tork, Chemical Catalog Co., 1926. (2) Schack, "Industrial Heat Transfer," tr. by Goldvchmidt and Partridge, p. 208, Braunworth I% Company, Inc., 1933. ( 3 ) seigle, fiev. ind. min.,1925, 349-74. RECEIVED April IO, 1935
Peyer (8) reported that it usually has an odor of acetic acid and sometimes that of trimethylamine. He found that, upon adding an excess of sodium hydroxide and boding a solution of the gum which had been previously hydrolyzed with dilute hydrochloric acid, a bron-n solution with an odor recalling that of benzaldehyde resulted. Gabel (4)compared it with tragacanth and found that it is more readily soluble and not as mucilaginous as tragacanth, and that, unlike tragacanth, its mucilages become thinner upon aging and the maximum viscosity of its mucilages is obtained without the aid of heat. A search of the literature failed to show any data on its colloidal properties.
General Properties Analyses of samples of powdered tears shoTv a moisture content of 11.60 to 15.31 per cent and an ash content of 6.07 to 6.96 per cent. The aqueous solutions have an acid reaction. Karaya may be distinguished from tragacanth by the greater amount of acid (1, 6, 9) which can be distilled from it over sulfuric or phosphoric acid and by the fact that it does not give a blue color with iodine solution (6). According to Jacobs and Jaffe (3, 6 ) , 1Iillon's reagent will give a white curdy precipitate when added to a solution of the gum, a reaction which distinguishes it from solutions of other g u n s which give precipitates of different appearance. Tschirch and Fluck (9) detect the presence of as little as 10 per cent of karaya in a mixture with tragacanth by a peroxide test Blue flakelets appear when a solution of the gum is treated with hydrogen peroxide and benzidine solutions. Karaya gum swells in 60 per cent alcohol, while tragacanth and acacia refuse to swell when the alcohol concentration is higher than 35 per cent (6). When a solution of the gum is boiled in dilute phosphoric acid under a reflux condenser, it turns pink or rose red (1). Electrophoresis experiments show migration of a negative colloid. When a solution of the gum is viewed under the microscope, three types of colorless masses are qeen. They resemble threads, feathers, or broken crystals. In addition, especially in the solutions of samples of the poorer grade.., brownish particles resembling broken crystals or woody debris are visible. The surface of a solution of the gum appears
INDUSTRIAL AND ENGIXEERING CHEMISTRY
1216
iAMMERED COPPER
RUBBER STOPPER
I
I
G L A S S TUBE
CAPILLARIES OF VARIOUS LENGTHS AND BORES
FIGURE1. VISCOXETERFOR KARAYAGuu SOLUTIONS to the eye to have corrugations which are particularly noticeable when a fairly thick solution is in motion.
Apparent Relative Viscosity Gabel (4) determined the viscosity of his solutions with a MacMichael viscometer but realized that he did not thereby measure the desirable properties. Therefore he devised his “flow test” which measures the time required for a 30-inch (76.2-em.) column of solution to flow from a glass tube of 1cm. bore. This test serves only for qualitative comparisons because the time required for a dilute solution to flow from a tube of so large a diameter is too small to be measured accurately, and because turbulent motion would be set up a t such rates of flow. With a tube of the diameter mentioned, it would be difficult to obtain the viscosities of the solutions in terms of the viscosity of water. The suspensions of karaya gum contain rather large particles which absorb or adsorb water and thereby become more or less permanently suspended and impart a lack of fluidity to the water. This power to impart lack of fluidity t o water is the desirable property of the gum. Preliminary experiments had shown that the logarithm of the time of flow of karaya gum solutions through tubes is approximately proportional to the concentration of the gum. Plotting the results of Gabel (4),logarithm of viscosity (MacMichael) against concentration gave a roughly straight line. But this line has a smaller slope than can be had by plotting the results obtained by measuring the time required to flow through tubes. Therefore the two methods do not measure the same properties. It would appear that the desirable property, the lack of fluidity which the gum imparts to water, can best be measured by taking the time required by its suspensions to flow through tubes. Furthermore it is desirable to express this lack of fluidity in terms of the viscosity of water and t o find a relation between the apparent relative viscosity of the suspensions and the concentration of the gum.
Experimental Procedure
PREPARATION OF SOLUTIONS.When the powdered gum was
mixed with water, there was a tendency to form clumps with gelatinous membranes which prevent the water from coming into contact with the gum in the interior. The easiest way t o dissolve
VOL. 27, NO. 10
the gum quantitatively was to brush the weighed sample onto the weighed or measured water contained in a rather large-mouthed bottle fitted preferably with a screw cap. Some glass shot (25 to 50) were added. Violent shaking a t the beginning and three or four more times during a period of 4 to 5 hours resulted in complete solution of concentrations up to 1.5 per cent, It was also desirable to shake the solution thoroughly after 4 or 5 hours, when hydration was more complete, in order to obtain uniform suspensions. The apparent relative viscosity may increase very slowly after a period of 24 hours for about a week. THEVISCOMETER.The use of the Ostwald type of viscometer n.as out of the question because of the great variation in viscosities involved and because of the stickiness of the solutions. Therefore the apparatus shown in Figure 1 was devised. It is essentially a funnel of very wide angle from which the fluid flows first through a tube of larger bore and then through a capillary or other tube of smaller bore with a total pressure of about 33 cm. at nearly constant level. There is a pressure drop of only 2 mm. with the passage of 10 grams of liquid. The primary tube is a capillary tube of small bore, is about 20 cm. in length, and is sealed to the larger tube. It must allow 10 grams of wat,er at 25” C. to run through without turbulent motion in no less than 40 seconds with a head of 33 cm. Tube 2 may consist of a shorter piece of the same capillary or of a capillary of slightly larger bore sealed to the larger tube, giving an over-all length of about 29 cm. Tubes 3 and 4 are similarly made, using capillrtries of larger bore. A tube of 4.5-mm. bore and 9 cm. in length was sealed to the tube of 7-mm. bore to form tube 5. PROCEDURE. The solution was poured upon the apparatus to the desired level which was measured by a small rule held so that its lower end touched the top of the glass tube. A stopper closed the lower end of the tube. The liquid was allowed to run into a small beaker which rested upon the left pan of a small trip balance. The right pan held enough weights t o tare the beaker, and about 5 grams more. The stop watch was started when the solution running into the beaker tripped the balance. A 10gram (or other) weight was then placed upon the right pan. When the balance was again tripped to the left, the watch was stopped. CALIBRATION OF TUBES. The time required for 10 grams of water to run through tube 1 was iirst determined. A dilute solution of the gum (0.1 per cent) was run through this tube, and the time for 10 grams was taken. Then the time for 10 grams of the same solution to run through tube 2 was determined. Water will run through this tube with turbulent motion, but the solution must not. From the data obtained with tube 1, the relative viscosity of the solution was calculated. From the relative viscosity and the time required for the solution to pass through tube 2, the time necessary for water t o pass through tube 2 without turbulent motion could readily be calculated. Tube 3 was calibrated against 2 in a similar manner, 4 against 3, and 5 against 4. The time for 10 grams of water to run through the tubes used in this report was as follows: tube 1, 40.7 seconds; tube 2, 12.78; tube 3, 1.03; tube 4, 0.2215; and tube 5,0.0603. The tube chosen for the determination of the viscosity of a solution should not allow it to run through wibh turbulent motion, nor should the time required for the solution to pass through be excessive. Patrick (7) says: “In the Ostwald viscometer the apparent viscosity of these sols (lyophile colloids) will be found to increase as the rate of flow through the capillary is diminished; at high rates the measurements should more nearly approach the true viscosity.” Suspensions of some karaya gum samples behave like these lyophile TABLE I. EFFECTOF Low RATEOF FLOW ON VISCOSITY VALUES Sam-
Time
Nd Oe.
Flow
30
3119
of
88 sec. 3 1 3 sec. 2 7 . 8 min. 6 2 5 min. 127 sec. 216 min.
Apparent Relative Ylscosity
Samde
1455 1413 1604 2933 572 1014
19 14
9 0 . 3 sec. 4 26 3. 25ssec. ec.
1505 31060 .91
1 0 9 . 3 8ec. 1 0 9 sec.
2.68
19
NO.
Time of Flow
107 min.
Apparent Relative Viscosity
493 502
colloids and give too high values when the time required for passage through a tube is excessive; suspensions of other samples have a tendency to give values for the apparent relatire viscosity that are too low when the time required for
ISDGSTRIAL ASD ENGINEERING CHEMISTRY
OCTOBER, 1935
pa'bage through the tube is rather long. Table I bhow exsniples of variations obtained in viscosity values by decreasing the rate of flon-. duspenqions of the two samples giving high values when the rate of flow is high show large feathery masses under the microscope. iTThen these thick suspensions are passed through a tube of -mall bore, an additional resistance to flow is proliably encountered because these relatively large particles must be crowded through a small orifice. The suspensions of the gum are by no means homogeneous, and it is possible that the more fluid portions break away to enter and flow through the tube, thus giving low results when the rate is decreased by using a tube of smaller bore and a sample giving particles which do not swell to such large proportions. The temperature of the room and of the solutions while the determinations were made was 25" * 1' C. as registered by qensitive thermometers. Among the many determinations made, occasionally a result was obtained which was clearly out of line with the other values. An explanation is that the particular solution had not been prepared properly and that the gum particles had
4000
3000 2000 IO00 800 600 400
&ice we are dealing, not with finely homogeneous suspensions, but with relatively large, irregularly shaped masses which sn-ell and tangle up with one another to give an apparT - ~ B L1E 1. COSCENTRATION AND APPARENTRELATIVE VISCOSITY (Solutions 24 hours old: temperature, 25' C.) Apparent Apparent Apparent C = Grams Relative Relative Relative Gum/100 Viscosity Viscositv viscosity Grams of Sample K = L o r of Sampie K =Log c>f Sample K = Log Hz0 19 (q-l)/C 30 (q-l)/C 14 (?-1)/C 0.2 0.3 0.4 0.6 0.8 1.0 1.4
'
'
LJ
5 a
100 80 60
40 30
a4 0.6 a8 1.0 1.2 1.4 G.GUt.4 PER 100 G. WATER
0.2
FIGURE2. LOGARITHMOF
INCREASE IN A P P . I R E s r REL.4TIVE VISCOSITY US. CONCESTRATIOX
not reached the same state of hydration as the other solutions. A repetition of the determination with a new solution usually gave results of the expected magnitude. Determinations can be repeated with new solutions of the same sample with results differing usually less than 5 and rarely more than 10 per cent.
Results of Experiments The results for three samples are shown in Table 11. Sample 19 is a typical high-grade gum, containing almost no brown maszes and a fen- crystal-like particles. Sample 30 is a very high-grade gum, containing almost no crystal-like particles and large numbers of rather large feathery masses. Sample 14 is of a fairly good grade but has more brown and crystal-like particles. Since all factors affecting the apparent relative viscosity of karaya gum solutions have not yet been determined, and
2.16 2.09 2.22 2.20 2.24 2.25
2.23 2.23
1180.0
4.53
,
.23 14.5
43.6
134.0 303.0 1413,O
4060.0
2.74
2.65 2.82 2.72
2.67 2.48 2.63 2.58
3.39 4 87 7.32 18.95 48.2 137.0 348.0 si5 0
2.66
Av. 2 . 2 1
1.89 1.96 2.00
2.09
2.09 2.13 2.12 2.10
2.05
ently high viscosity, an empirical equation expressing the relation between this viscosity and the concentration is all that can be expected a t present. That the logarithm of the viscosity of highly viscous solutions is proportional to the concentration has been reported in the literature-for example, by Berl and Umstatter (2). The logarithm of the viscosity of karaya gum solutions is proportional to the concentration only when the viscosities are high; the viscosities of solutions of low concentration 'are too high to fit into that relation. When, however, the logarithm of the increase in the viscosity of water is plotted against the concentration, a straight line is obtained (Figure 2 ) . The equation for this relation may be expressed : where
z
3.70 5.25 8.75 22.0 63.3 178.0 495.0
1.2
t 300 $200
1217
log ( v ~ - T o ) / C= K relative viscosity of soln. viscosity of water = 1 C = concn. of gum, grams/100 grams water K = a constant
(1)
qs = 90 =
Table I1 gives the results for the three samples. The values for K are reasonably constant. The value for K of sample 30 shows a tendency to decrease with increasing concentration. This tendency may be explained by the fact that this sample has larger feathery masses which offer additional resistance to flow through capillaries of small bore. It is possible to obtain anomalous results with samples of different types. Solutions of low and approximately the same viscosity may have the order of their time required for passage through a tube of small bore reversed when allowed to pass through a tube of somewhat larger bore or shorter capillary. The value K depends upon the amount of active material in the sample which takes up water, the size, shape, and rigidity of the particles-in fact, all of the factors which tend to decrease the fluidity of the water. The relative efficiency of the samples can be obtained by reading from the curves or calculating the amounts of gum required to give the same relative viscosity. Giving sample 30 a value of 100, the relative efficiency of sample 19 is 85.6 and of sample 14 is 79.4. The apparatus, procedure, and logarithmic relation already discussed have been found to be a valuable aid in evaluating gums offered for sale or received. The price of the gum depends a great deal upon the color of the particular supply. It is possible to effect economies in the use of the gum if its color is not important by finding a supply which is cheaper but high in viscosity-producing power. From Equation 1, Equation 2 can be derived : qr
-1
= (TI -
l)C2C1
(2)
from which the viscosity v2 of a solution of concentration Cz can be calculated from the viscosity vl obtained from a solution of concentration of C1 of the same sample.
