DEAD SEA SALTS IN COSMETIC EMULSION 11 amount of added DS salt was increased (12). This behavior can be observed in Figure 8. A sudden change in conductivity curves can be seen at salt concentrations of 0.07 and 0.15 wt%, corresponding to the observed maximum viscosities. This result suggests that the added ions to the system at these concentrations have a more pronounced effect on the emulsion structure, leading to an increase in viscosity, than does the free water, which leads to an increase in conductivity. A decrease in the conductivity values of body cream samples with storage time up to four months can be also seen in Figure 8. This is an expected result of water evaporation during the storage period. As shown in Figure 9, the conductivity of the salt-free cream stored for four months decreases with the storage temperature. The conductivity values of the body cream samples decreased during the four months of storage over the entire range of storage temperatures. A decrease in the conductivity values with increasing storage temperature at constant storage time can be clearly observed. A low conductivity value reveals that there is more lamellar water and less free water in the cream, which can be seen as an increase in the viscosity of the cream (13 ). The largest change in conductivity during storage was observed for the sample stored at 45 ° C. This cream previously had a maximum viscosity related to the increase in water evaporation at this condition. Figure 10 shows that the conductivity of a body cream sample containing 0.07% DS salt content decreases with both storage time and storage temperature. The largest and the sharpest changes in conductivity during storage were observed for the sample stored at 45 ° C, which exhibited a maximum viscosity, as shown previously. � ' u ::J ""C C 0 (.) 200 150 100 50 0 0.00 0.05 Storage conditions: room temperature Storage period: -D-- One week -+- Two months -----A- Four months 0.10 0.15 Salt concentartion (w/w % ) 0.20 0.25 Figure 8. The effect of DS salt concentration on the conductivity of body creams stored for different periods at room temperature.

12 JOURNAL OF COSMETIC SCIENCE 80 8 ° C room temperature - 60 -E � 40 room temperature ·s;: :J "C 0 u 20 Salt concentration = 0% 45 °C 0 0 40 80 120 Storage Time (day) Figure 9. The effect of storage time on the conductivity of a salt-free cream sample stored at different tern peratures. 120 110 - E 100 � ·s;: 90 :J "C 80 0 u 70 � e•c -EB- room temperature 45 °C ---- 46 °C 60 0 40 80 120 Storage Time (day) Figure 10. The effect of storage time on the conductivity of a cream sample containing 0.07% DS salt and stored at different temperatures.