STARCH STUDIES Gelatinization of Starches in Water and in Aqueous Pyridine JAMES W. MULLEN
1 1 1 AND EUGENE PACSU Princeton University, Princeton, N. J.
HE following study was conducted with a twofold pur-
tion; the lowest gelatinization temperatures was in 30 per pose in view: first, to furnish quantitative data on the cent pyridine. Other critical gelatinization curves were obprocess of gelatinization of starch; secondly, to detertained in 60 per cent (azeotropic) and 50 per cent pyridine. mine the optimum conditions for the preparation of starch The effect of starch concentration was studied in these three for esterification by a method previously described (10). critical concentrations of pyridine with 10, 15, and 20 per Gelatinization has been the subject of much study. It is cent potato starch as well as with 10 and 15 per cent cornwell known that starch granules swell and begin to burst bestarch. Further, these three curves were studied for 15 per tween rather definite temperature limits, and also that these cent suspensions of tapioca, wheat, and rice starch. The temperature limits may be altered by the addition of certain gelatinization curves in pure water are included for comparipeptizing agents. For example, both potassium thiocyanate son. The heat of gelatinization was determined on 15 per and urea cause gelatinization at room temperature. Less cent suspensions of the five species mentioned above, both in well known but equally obvious are the heat effects which pure water and in 30 per cent pyridine, since a t the latter accompany gelatinization. It is probable that a complete concentration pyridine was shown to have its greatest pepstudy of these heat effects will be more influential in the solutizing effect. tion of the problems presented by gelatinization than any other factor. Briefly, the gelatinization process is strongly Materials endothermic. There is a lesser exothermic effect accompanyThe potato, corn, wheat, rice, and tapioca starches were ing the hydration of dried starch with which we shall not deal commercial mobucts selected for their close resemblance to a t oresent. To augment with further auantitative data the m&y studies (1I)"that have been maie upon the general the natural 'product; that is, no chemical treatment was employed in their preparaprocess of gelatinization, and tion. The moisture contents the relatively few and inof these starches were decomplete studies (6, 7, 8) Gelatinization of potato, tapioca, wheat, termined by drying over P106 that have been carried out corn, and rice starch was studied in waterat 20 mm. of mercury and on the heat effects, is the first pyridine mixtures of concentrations rang20' C. for 6 hours, after aim of this paper. ing from pure water to pure pyridine. The which time the temperature As to our second purpose, was raised to 110" C. The the interest in starch esters gelatinization of these starches was folmoisture contents were as has increased rapidly within lowed by consistometric methods furnishfollows: pQtato, 17.4 per cent; the past year (6, 9,10, 19, 13). ing data relative to the temperatures, corn, 10.2; wheat, J0.7; rice, The method of preparation consistencies, and heats involved in the 9.5; tapioca, 11.9. I n the described by the authors inprocess. Correlation was established beactual experiments the moist volves the use of pyridine starch was used and the as the catalyst. Critical comtween these factors and the granule sizes Concentration of the pyridine parison of the different methof the different starch species. The disadjusted in the light of these ods of esterification is reaggregation of the starch granules appears figures. served for a forthcoming paper. to reach a more advanced stage in a mixture For the runs in pyridine For the present it is sufficient to containing 30 per cent pyridine than in determine the effect on gelatiniabove 60 per cent concentration zation of pyridine solutions of pure pyridine (boiling a t 113any other concentration. It was also found 115.5" C.) was diluted with the various concentrations. that the heat absorbed during gelatinizaI n the present work 15 per proper amount of water. For tion is more than ample to furnish energy cent suspensions of potato the runs with 60 per cent for breaking one to two hydrogen bonds starch were gelled in aqueous pyridine or less, the pyridineper glucose anhydride unit. solutions of pyridine varying waterazeotrope wasused. This azeotrope consists of one mole by 10 per cent increments from of Dvridine to three moles of pure pyridine to pure water. The cobistency thoughout gelatinization was followed by water and boils a t 93' C. (4) u&er normal pressure. Calan adaptation of the method of Caesar (1, 9). A method culation shows this to be approximately 60 per cent pyridine involving the mechanical meawurement of the torque on the and 40 per cent water by weight. An attempt was made to stirrer had been tried but found to be less sensitive than the check this figure by titrating for pyridine with 2 N hydroelectrical measurement. Gelatinization did not occur in chloric acid, using methyl orange as the indicator. Results suspensions of greater than 60 per cent pyridine concentrawere reproducible, but approximately 1 per cent low. Study of the p H values involved indicate that this is to be expected 1 Permanent address, 4909 Cary Street Road, Riohmond. Va.
T
802
Vol. 34, No. 7
INDUSTRIAL AND ENGINEERING CHEMISTRY
808
as a result of end point error. I n the 60 per cent run sufficient pure pyridine was added to correct for the moisture content of the starch.
Apparatus and Procedure The apparatus is shown in Figure 1. I t consists of a doublewalled stainless steel kettle equipped with an anchor-type stirrer, fractionating column, heating system, thermometer well, and dump valve.
FIGURE1.
PHOTOGRAPH O F APPARATUS
The stirrer is driven at 85 r. p. m. by a l/s-horsepower synchronous motor, This provides constant speed at any load so that an increase in consistency of the starch paste is reflected only in the electric power consumed by the motor. To be exact, there is a heat loss proportional to the square of the current drawn and the internal resistance of the motor, Z2R,. In practice this correction was omitted since the power increase throughout gelatinization took place over such a short time that heat losses were negligible. The kettle was heated by Dowtherm supplied to the jacket. The Dowtherm was circulated by a small electrically driven gear pump at a constant rate across three 1500-watt electric heaters. A thermostat between the kettle and the heaters furnished precise temperature control. The fractionating column consisted of 8 feet of 3-inch Pyrex glass pipe packed for the first foot of its length with l/Z-inch beryl saddles and for the next 5 feet with '/&-inchsaddles. The top 2 feet were left open and uninsulated. This section, in connection with a small stainless steel finger condenser, controlled the reflux ratio. The main condenser consisted of a vertical 4-fOOt length of 1-inch stainless steel tubing jacketed with a length of 2-inch black iron pipe. This seemingly elaborate distillation setup has an important bearing upon the starch ester studies where pyridine recovery is the controlling economic factor. In studying the effect of aqueous pyridine upon the various species of starch, the follorTing procedure was employed: The total contents of the kettle were always 5 kg. This weight was made up from starch (allowing for moisture), pyridine, pyridine azeotrope, and/or water. Stirring was continued until a constant zero value was recorded upon the wattmeter registering the power requirements of the motor. The heateis were then started, raising the temperature at an average rate of 3" C. per minute. The gelatinization was followed by noting wattmeter readings for each degree. Increase in consistency throughout the gelatinization process was measured by increase in watts above the initial zero value. The results are given as plots of wattage against temperature. The results were found reproducible t o within 1 watt along the consistency axis and t o less than 1" C. along the temperature axis. Separate experiments were made t o determine the heat effects throughout gelatinization. Here again, a total of 5 kg. was used, consisting of 15 per cent starch in either pure water or in 30 per cent pyridine. The temperature increase was followed with respect t o time. The temperature was recorded every 30 seconds. The increase of the Dowtherin temperature was found
to proceed at the same rate over the entire range of gelatinization whether pure water or starch was being heated in the kettle; suspicion of difficulties in heat transfer to the jellylike starch pastes was thus eliminated. The results are given as graphs of temperature against time. Finally, average granule sizes of the starches used were determined microscopically.
Gelatinization Results Figure 2 gives the results of the gelatinization of 15 per cent potato starch in aqueous pyridine, the concentration of which is varied by 10 per cent steps from pure pyridine (actually, approximately 99 per cent pyridine due to the moisture in the starch) to pure water. Although readings mere taken for each degree, only the critical points are given to avoid confusion on the graphs. It is obvious from Figure 2 that concentrations of pyridine greater than 60 per cent have no measurable su elling effect upon starch. Apparently the forces that make up the pyridine azeotrope are sufficiently strong to tie up the water molecules and leave none free to swell the starch. Swelling begins in 60 per cent (azeotropic) pyridine, but is erratic and results in a lower consistency than in all the other cases. The maximum consistency is greatest for 50 per cent pyridine; it then decreases t o a minimum value a t 30 per cent pyridine and again rises until 10 per cent is reached. The maximum consistency for pure water is less than for the 10 per cent run but greater than for that of the azeotrope. I n all cases the gelatinization temperature (as defined by the temperature a t which the rate of increase in consistency reaches its greatest value) is lower in aqueous pyridine than in pure water. The lowering follows practically the same sequence as the maximum consistency. Starting with pure water, i t decreases steadily until the 30 per cent run is reached. From this minimum it rises to the 60 per cent run. 7-
40t 5 20 -
% 3 -
POTATO STARCH 15 X
30
30
3P 1 0-.d
n
g
-
V
0
70-80 90 I O 0 X I
I
40
I
I
50
I
I
I
GO
Temperature
I
I
70
I
80
I
I
90
"C
FIGURE 2. GELATIIVIZATION OF 15 PERCENTCONCEIVPOTATO STARCH I S V-4RIOUS CONCENTRA-
TRATION OF
TIONS O F AQUEOUs P Y R I D I N E
It is apparent that there are four critical curves: the pure water run which exhibits the highest gelatinization temperature, the 30 per cent run which shoir s the lowest gelatinization temperature, the 50 per cent run which exhibits the greatest maximum consistency, and the 60 per cent run which represents the greatest pyridine concentration capable of swelling starch. The effect of starch concentration on these
INDUSTRIAL AND ENGINEERING CHEMISTRY
July, 1942
809
zation in both pure water and in 30 per cent pyridine. The rate of heating up to the gelatinization point was so nearly identical in all cases that only the curve for one case is shown. It is apparent from these curves that heat is strongly absorbed within the same temperature ranges between which the increase in consistency is greatest; i. e., the swelling process is endothermic. The heating rates of the starch pastes become equal after the gelatinization process to the calibration heating rate of pure solvent; that is, the upper portions of the curves become parallel. Therefore, it is necessary only to measure in minutes the displacement of the curves for starch from the calibration curve for the water equivalent of the paste t o obtain a measure of the amount of heat absorbed. The product of the heating rate (in degrees per minute) between the temperature limits involved times the displacement (in minutes) times the water equivalent of the absorbing mass (in grams) give the number of calories absorbed:
30 X
A
3 40
2
S x min. x grams = cal. = grams x
min.
C
0
C.
Y .d
A value of 0.3 calorie per O C. was assumed as the specific heat of starch. The amounts of water and pyridine, as well as their specific heats, were accurately known. The chief source of error in determining the water equivalent lies in the lack of knowledge of the amount of heat absorbed from the stirrer, thermometer well, etc. However, the values given later as the heats of gelatinization, even after reasonable assumptions are made, are probably not accurate to more than 1 kg.-cal. per mole CaH1,05 unit (i. e., 162 grams). The relative values between starch species represent a higher degree of accuracy.
30
P
3
.d
2 20
10
40
50
70
60
Temperature
C '
.
80
00
FIGURE3. GELATINIZATION OF 20, 15, AND 10 PER CENT CONCENTRATIONS OF POTATO STARCHESIN VARIOUS CONCENTRATIONS OF AQUEOUS PYRIDINE
50 %
-
CORN STARCH 15% 10%
C
.d
four critical curves is shown in Figure 3 which represents the results of the gelatinization of 20, 15, and 10 per cent potato starch in pure water, 60 per cent, 50 per cent, and 30 per cent pyridine. The general arrangement of the curves is the same as in Figure 2. The maximum consistency for each run a t a given pyridine concentration depends directly upon the percentage of starch present. For example, the upper curve in the 30 per cent series represents the gelatinization of 20 per cent starch whereas the lower curve represents the gelatinization of 10 per cent starch. The peaks in a given series fall almost directly below one another; however, there is a slight but real displacement within a series to lower temperatures with increasing concentrations. This was shown previously by Caesar to be true in the case of gelatinization of starch in pure water. He attributes it t o the fact that in the more concentrated pastes the swollen granules are more closely packed and the higher shearing strains thus imposed cause an earlier breakdown. He also explains the shift of the initiation point of gelatinization as due to a latent heat effect which becomes larger with increasing concentration. On the whole these results hold true in the case of different species of starch. The general arrangement of the curves is the same although their actual shapes may vary considerably. Figure 4 gives the results of the gelatinization of cornstarch in 10 and 15 per cent concentrations at the four critical concentrations of pyridine. Figure 5 shows the same results for rice, wheat, and tapioca starch but only in 15 per cent starch concentrations. Figure 6 gives the rate of temperature increase for the different species of starch throughout the process of gelatini-
20
x
2
3
4 IO El
v
40
50
60
Temperature
70
"C.
BO
90
FIGURE 4. GELATINIZATION OF 10 AND 15 PERCENT OF CORNSTARCH IN CRITICALCONCONCENTRATIONS CENTRATIONS OF AQUEOUS PYRIDINE
The curves of Figure 6 indicate that! the heats of gelatinization vary considerably among species, potato starch requiring most and rice least. It is also apparent that more heat is required to gelatinize starch in 30 per cent pyridine than in pure water. The heat absorbed varies between species in the 30 per cent pyridine series, with wheat exhibiting the maximum absorption. These facts will be treated more fully in the discussion of results. The heat of gelatinization was also measured for 1.5 per cent potato starch in 50 per cent pyridine and will be treated later. All of the above results are summarized in Tables I to IV. The average granule sizes of the starches involved were taken from Figure 7 and are given in Table 111.
INDUSTRIAL AND ENGINEERING CHEMISTRY
810
Vol. 34, No. 2
Discussion of Results Table I reveals that for all species the lowest minimum consistency occurs in 30 per cent pyridine. The 30 per cent pyridine paste is always smooth and transparent, whereas the others are more liable to exhibit lesser degrees of physical and optical homogeneity. Table I1 shows that these same results exist within a given species when concentration is varied. These facts lead to the conclusion that the disaggregation of the granules is most complete in 30 per cent pyridine. I n Table 111-A the different species of starch are listed in the order of their increasing gelatinization temperature. This is also the order of decreasing heats of gelatinization and agrees remarkably well with decreasing order of maximum consistency and grain size. Wheat starch gives erratic results. Examination of the gelatinization curves of the 15 per cent starches in pure water shows that, of all species, wheat alone fails to give a sharp curve. An explanation for these deviations of wheat starch may be found from Figure 7; wheat shows the widest variation in granule size. If, as indicated in Table 111-A, low gelatinization temperature corresponds to large grain size and vice versa, then the wide gelatinization range and low maximum consistency of wheat starch are probably due to a combination of effects of the gelatinization of the large and small granules of which it consists. Stated another way, wheat starch consists essentially of large granules and small granules (greatest deviation from the mean). The aberrant gelatinization effects are then due t o a n early swelling of the large granules followed by the later
20
10
- R I C E STARCH
50%
-
0
h
v)
30t
WHEAT STARCH
I5 %
I
t
s -.-
2o
C
10
P 0,
+ v)
.d
e o
u
T A P I OCA STARCH
20
-
TABLEI. CHARACTER OF 15 PER CENT STARCH PASTES IN AQUEOUSPYRIDINE Staroh Potato
% CsHsN 0
30 50
60
Tapioca
23.0 28.5 38.5
17.0
5.5
12.0
Clarity0 Transparent Transparent Opaque Opaque
26.0 28.0 29.8 16.0
10.0 6.5 8.6
Smooth Smooth Smooth Doughy
Transparent Transparent Translucent Translucent
0
15.7 21.7
11.1 7.5 11.6
Doughy Smooth Lumpy Lumpy
Opaque Transparent Translucent Opaque
8.8 4.4 9.2 15.5
Doughy Smooth Doughy Lumpy
Opaque Trans arent Transrueent Opaque
7.6
Lumpy Smooth Lumpy Lumpy
Opaque Transparent Translucent Opaque
60
30 50
60
21.5 14.2
Corn
0 30 50 60
21.7 17.0 26.0 19.5
Rice
0 30 50 60
19.8
a
9.0 11.0
Quality" Smooth Smooth Doughy Lumpy
30 50
0
Wheat
Consistency, Watts Max. Min.0
19.5 10.0
15.8
11.0
4.0
4.5 5.4 10.2
At 9 3 O C.
TABLE 11. CHARACTER OF POTATO STARCH PASTES IN AQUEOUS PYRIDINE % Starch % CsHsN 10
l5
0 30 50 60
0 30 50
60 20
0
At D3' C.
0 30 50 60
Consistency, Watts Max. Min.a
13.9
19.2 14.5
9.5
23.0 28.5 38.5 17.0
37.6
43.0 83.0 30.4
Quality0 Smooth Smooth Smooth Lumpy
Clarity0 Transparent Transparent Translucent Opaque
11.0
12.0
Smooth Smooth Doughy Lumpy
Transparent Transparent Opaque Opaque
19.2 10.6 20.0 27.5
Smooth Smooth Doughy Lumpy
Transparent Transparent Opaque Opaque
6.0
5.0 5.4 7.5 9.0 5.5
10
-
30
40
50
60
Temperature
70
80
90
"C.
FIGURE 5 . GELATINIZATION O F 15 P E R CENT COKCENTRATHREB STARCHES IN THE CRITICAL CONCENTRATIONS OF AQUEOUSPYRIDINE
TIONS OF
swelling of the small granules. The large granules have started to burst before the small granules start t o swell. This accounts for the slow rise of the gelatinization curve over a wide temperature range as well as for the low maximum consistency. These effects are true for all the starch species, but are to a lesser degree due to a smaller deviation of the extreme granule sizes from the mean granule sizes; i. e., the starches behave more as if they consisted of a single granule size. This problem of the effect of granule size upon gelatinization temperature has been the cause of much discussion. Among the most recent work on this subject is that of Cook and Axtmayer (3). They maintain that granule size influences the temperature of initiation of gelatinization but not the rate of gelatinization. That granule size is not the only factor contributing to the maximum consistency of a paste is seen by examining the value for tapioca starch. Obviously the thick tapioca pastes are subject to other influences than grain size alone. Table 111-B discloses results similar to those just discussed except that gelatinization took place in 30 per cent pyridine. For the starches listed in the same order as above, the increase in gelatinization temperature with decrease in granule size became much less. I n fact, the gelatinization temperature
INDUSTRIAL A N D ENGINEERING CHEMISTRY
July, 1942
Water Equivalent
3750 g.
HEAT OF ATlNl ZATION
40E-
GELATIN1 ZATION 15%STARCH IN 30% PYRIDINE
15xSTARCH IN WATER
0
15
0
Time
811
5
10
15
-
20
(in Minutes)
FIGURE 6. VARIATIONIN HEATSOF GELATINIZATION became almost constant at a little over 40' C. The heats of gelatinization also showed a slight downward trend but again became more nearly constant. Maximum consistencies vary directly with granule size. Again wheat falls somewhat out of line, this time exhibiting the lowest gelatinization temperature (32' C.) ; however, if we consider gelatinization temperature and not granule size to be the determining factor in the amount of the heat of gelatinization, the data fall into line in that in 30 per cent pyridine the largest heat of gelatinization is exhibited by wheat. It is interesting to note that, whereas the gelatinization curves for wheat starch in both pure water and 50 per cent pyridine have a gentle slope instead of the sharp break as shown by the other curves, the curve in 30 per cent pyridine looks more like the corresponding curve for the other species. If the sloping curves are due to the granule size effect as described above, the gelatinization in 30 per cent pyridine must be so rapid and complete as to smooth out this effect. This is in agreement with the high peptizing effect of 30 per cent pyridine already described. This also is com-
Potato
Tspiooa
Wheat
patible with the fact that the total amount of heat absorbed is greater for gelatinization in 30 per cent pyridine. These views are acceptable if we consider gelatinization as a rate process somewhat similar to the denaturation of proteins. For example, a n egg may be kept at a temperature only a few degrees below its denaturation point for an extreme length of time without showing any change; however, if we raise the temperature by the necessary small increment, hardening occurs at a rapid rate. Similarly, a 15 per cent aqueous suspension of potato starch may be kept a t 60' C, for long periods without any increase in consistency. A t 61.5' C., however, gelatinization has commenced t o show rapid progress. The temperature a t which these rate processes are initiated depends upon the medium in which the starch is gelatinized. Gelatinization occurs a t room temperature in a saturated solution of urea, whereas the effect of different concentrations of pyridine has just been discussed. No attempt will be made to theorize on the significance of this heat effect. Obviously one is operating against t h e
OF hm0~108 ( A F I Q 7.~ PHOTOMICROORAPES
corn Riae ~ P B o ~ X ~ Zoo) ~ ~ L Y
INDUSTRIAL AND ENGINEERING CHEMISTRY
812
TABLE111. GELATIKIZATION OF 15 P E R C E K T S T - R C H WATERAND IN 30 PERCENTPYRIDIKE
IN
-B. In 30 Pyridine---A. In Water-Gel. heat Max. Gel. reat hiax. oonsistGrain Gel. small cal.) consis- Gel. small G a l . / Shea, ttmp.b, CeHioOs tency, temp., CeHloOa ency, O C. unit watts starch Microns C. unit watts 11,500 28.5 23.0 40.0 35 61.5 9080 Potato 26.0 11,300 28.0 41.5 16 63.5 8780 Tapioca 15.7 32.0 11,750 21.7 16 65.0 7300 Wheat 21.7 42.5 10,600 17.0 7100 13 68.5 Corn 19.5 43.0 9,500 10.0 4 75.0 5700 Rice -a 5
Average values. Defined in the text.
TABLE I\-. GELITIRIZATIOX OF 15 PER C E N T IS A Q G E O UPYRIDIKE ~ I CbHaii 0 30 50
Gel. Temp., 0
c.
61.5
40.0 46.2
Gel. Heat. Small Cal./CsllloOs l-nit 9,080 11,500 8,200
POTATO
STARCH
Max. Consistency, Watts
23.0 28.5 38.5
forces which are responsible for starch taking a granular form. What those forces are is speculative. The presence of hydrogen bonds in starch is yet to be proved. However, the heats of gelatinization given above are of the right order of magnitude to furnish energy for from one to two hydrogen bonds per Cg unit. The facts are suggestive. Finally, Table I V compares the effects of different concentrations of pyridine. The low value of the heat of gelatinization may be taken to mean that incomplete diaruption of the starch granules has taken place. This is plausible considering that above 60 per cent no effect occurs. The high
Vol. 34, No. 1
maximum consistency is agreeable if we consider that in the 50 per cent paste a maximum number of partially swollen granules and a minimum number of unburst granules are present.
Acknowledgment Jf7e gratefully acknowledge the financial assistance given by the Research Corporation, of New York, which made this investigation possible. '1Tle further wish to thank Stein, Hall & Company, Inc., and the Corn Products Refining Company for their generous supply of starches.
Literature Cited (1) Caesar, G. V., IND. ENG.CHEM.,24, 1432 (1932). (2) Caesar, G. V., and Moore, E. E., Ibid., 27, 1447 (1935). (3) Cook, D. H., and Axtmayer, J. H., IND. E N G .CHEM.,A N ~ LE.D . , 9. 226 (1937). (4) Heilbron, "'Dictionary of Organic Compounds", Oxford Univ. Press, 1938. (5) Kuntsel, A,, and Doehner, K., Kolloid-Z., 88, 209 (1939). (6)Mack, D. E., and Yhreve, R. N . , IND. ENG.CHEM.,34, 304 (1942). (7) Nazarov, V. I., and Nikolaev, A. V., Compt. rend. acad. sci. U . R. S. 8..20, 569 (1938). (8) Ibid., 24, 263 (1939). (9) Nisida, T., Japanese P a t e n t 130,827 (June 29, 1939). (10) Pacsu, E., and Mullen, 3. W., 11, J . Am. Chem. SOC.,63, 1487 (1941). (11) Radley, J. .4.,"Starch and I t s Derivatives", p. 29 et seg., New York, D. V a n Nostrand Co., 1940. (12) Seiberiioh, J., Rayon Textile Monthly,, 22, 605,686 (1941). (13) Whinfield, J. R., and Ritchie, G. G., Brit. P a t e n t 535,949 (April 28, 1941). BASEDupon a thesis submitted by James W. Mullen I1 t o the faculty of Princeton University in partial fulfillment of the requirements for the degree of doctor of philosophy.
COCONUT SHELL CHARCOAL Effect of Concentration of Zinc Chloride and of Hydrochloric Acid on Activity LIU-SHENG TS'AI AND KUNG-YAO CHUANG Y enahing University, Peiping, China
The effect of concentration of zinc chloride and of hydrochloric acid on the activity of coconut shell charcoal has been studied by varying each separately. In the case of hydrochloric acid the activity increases at first rapidly and then very slowly with increasing concentration. In the case of zinc chloride the activity increases and rapidly reaches a maximum. In general, the results favor the dissolution theory of activation, i n which i t is assumed that complex ions are formed which cause the cellulose to be dissolved.
LTHOUGH treatment with zinc chloride and hydrochloric acid solutions is used on an industrial scale for the production of activated charcoal, little is recorded in the literature on the effect of the concentration of either of these solutions on the activity of the charcoal. A search revealed only one paper (1) dealipg specifically with the effect of zinc chloride concentration, nothing was found concerning the effect of varying the concentration of hydrochloric acid. With cellulose, lignin, and wood pulp as starting materials and the adsorption of methylene blue and iodine as a measure of activity, the activity reached a maximum with increasing concentration of zinc chloride (I). We desired to determine whether similar results would be obtained on coconut shell charcoal by the chloropicrin test. The effect of varying the concentration of hydrochloric acid was also measured,
A
Effect of Concentration TREATMENT WITH HYDROCHLORIC ACID. It was hoped that the results obtained from this investigation might be put directly into commercial practice. Therefore the chemicals used were all of commercial grade. I n carrying out this series of experiments, the amount of commercial hydrochloric acid was varied, while the weight of zinc chloride was arbitrarily fixed a t 520 grams. In each experiment enough
