Exercise 107. The Sol and Gel of Manganese Dioxide

The Sol.—Five grams of commercial glucose dissolved in 25 g. of water is made alkaline with a 10 per cent solution of sodium hydroxide. The solution is stirred in a freezing mixture while 100 cc. of a 6 per cent solution of potassium permanganate is slowly added (during 10 min. and at a uniform rate). 

The Gel.—As the mixture just described becomes warmer, it grows more and more viscous, until after 5 or 10 min. it jellies. After about Yi hr., syneresis starts 

Alternate Method.—To 20 cc. of a 6 per cent solution of potassium permanganate (at room temperature) add three drops of glycerin. A sol results which will gelatinize in from 5 to 10 min. The gel resembles in every way the one obtained in the former experiment. 

During the earlier stages of the liquefaction, observe the formation of globules of clear water (syneresis). 

With a fine capillary pipette drop some of the liquid into a large beaker of water, observing the formation of vortex rings. 

---