T H E VISCOSITY OF SOLS MADE FROM X-IRRADIATED APPLE PECTIN C. H. DWIGHT AND H. K E R S T E N Department of Physics, University of Cincinnati, Cincinnati, Ohio Received March 86, 1938
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INTRODUCTION
I n a previous paper (2) the authors described experiments upon the viscosity of sols which had been made from X-irradiated agar. It was concluded (i) that irradiation of dry agar by soft x-rays decreases the viscosity of the resulting sol, (ii) that there is no appreciable “recovery” of the dry agar from the effects of irradiation, a t least within seventeen days, (iii) that the effect on the agar is not due to heat emanating from the target of the x-ray tube, and (io) that irradiation of the dry agar slightly decreases the pH of the resulting sol. The present paper covers experiments upon apple pectin, with a view towards (i) the finding of an effect similar t o that observed in the case of agar, when the sol is made up of an irradiated sample, (ii) the extension of the “recovery time,” and (iiz) showing that pH plays probably only a minor part in the experiments. EXPERIMENTAL
As in the previous experiments, the x-rays were supplied by a copper target gas x-ray tube (1) operated a t 37 peak kilovolts and 10 milliamperes. The window of the x-ray tube was made of thin aluminum and Cellophane, so that the most inJense part of the radiation passing through it had a wave-length of 1.54 A. Powdered apple pectin was irradiated in the cavity of a drop-culture slide, placed about 3 em. from the focal spot of the x-ray tube. Each sample was irradiated for 3 hr., and, after having been irradiated, was mixed, and divided into several parts, each containing 0.12 g. These portions of the original sample were placed in flasks to which 20 cc. of buffer solution was added. pH concentrations from 1.76 to 6.95 were used. Control samples were made in exactly the same way, except that unirradiated pectin was used. In any one experiment three parts of a given sample, in buffersof as many different pH values, together with three controls, were employed. In order to insure uniformity in the diffusion of the powder within the liquid, the six flasks were placed in a rocking frame operated by an electric motor. The flasks, frame, and motor were placed in an electrically heated 1167
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DWIGHT A I D H. KERSTES
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oven, the temperature of which n-as kept at about 70°C. by a thermoregulator. -4decrease in the density of the sol, due to evaporation while being heated, was prevented by closing the tops of the flasks nith ruhber caps. -4fter agitation for 30 min. the motion was stopped, and the heater turned off. The flasks were then allowed t o cool for 2 hr., in which time the sole were assumed to hare reached room temperature and h a w ‘‘zrro age.” -4 definite amount of each sol was pipetted into six separate Ostnald Tiscoqity pipet;, which were so arranged that suction or pressure coiild he
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FIG.1 Plot of relative viscosity of sol against pH powders. Sols of same age.
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A , controls; B, irradiated
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FIG 2 Plot of relative viscosity against time io1 “recovery” of t h e pectin from the controls; B, irradiated ponders pH = 5 effects of irradiation 9,
applied singly or collectively t o them by connecting the top “bus” tube to a small rotary pump or to the laboratory air compressor, respectirely. l l u c h greater convenience and dispatch were thus effected. After the experiment the viscosity pipets could be washed and dried simultaneously. The time of flow of the sol through the viscosimeters was observed with a stopwatch, and divided by the time of flow of distilled water at approximately the same temperature through the same viscosimeter. This quo. tient was taken as the “relative viscosity” of the particular sol. Check
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X-IRRADIATED APPLE PECTIN SOLS
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readings were taken t o show that within the time of the experiment there was little or no (‘age” effect in the sol. The results obtained from these experiments are plotted in figure 1, which shows (i) that there is a marked difference between the controls (A) and the irradiated samples (B), (ii) that the effect of pH variation is unimportant, at least in comparison with (i), and (iii) that there is little effect due to the “age” of the sol, shown by the closeness of the points plotted at given pH values, throughout the time required for the experiment. In order to investigate the possible “recovery” of the apple pectin powder from the effects of irradiation, a relatively large amount of the pectin was irradiated and then set aside in a bottle identical with that which contained the control. At the end of five days a sample (0.12 g., as previously) was run through a Viscosity pipet, and the relative viscosity determined. A control was also run. This procedure was repeated a t the end of twenty-nine, fifty-seven, and eighty-five days. In each case a p H of 5.0 was used for the sol. Figure 2 indicates that there is little recovery of the powder even after two and a half months CONCLUSIONS
1. As was the case with agar, irradiation of dry apple pectin powder by soft x-rays profoundly affects the viscosity of the resulting sol. 2. The effect of p H variation is not very important in comparison with the effects due t o irradiation. 3. There is no appreciable recovery of the dry pectin powder from the irradiation, even after eighty-five days. REFERENCES (1) KERSTEN:Radiology 23, 60-3 (1934).
(2) KERSTEX AND DWIGHT: J . Phys. Chem. 41,687 (1937).
