ADSORPTION 519 



])riiitod sheet. Sliake the pieces nf ])a]ier in an Krlciiiiicyer Hask containing 

 water till the papers have l^ecoine waterlojij^ed and sink to the bottom of the 

 flask. Cover the water with a tliiii layer of a light mineral oil, and shake 

 thoroufrhly. When tlie oil and water have separated, the printed bits of 

 paper will be fonnd floating, print side upwards, at the oil-water interface. 

 The unprinted bits sink. Paraflin oil, the usual dispersion medium for printer's 

 ink, is a satisfactory oil to use. 



19. Demonstration of the Oxidation of Oxalic Acid when Adsorbed to 

 Charcoal. 



Air freed from COo (by passing over soda lime, caustic soda and baryta) 

 is sucked through a vessel containing charcoal, oxalic acid and water. The 

 CO., liberated bv the oxidation of the oxalic acid is pas.sed into lime or baryta 

 water which becomes turbid. 



Arrangement of . apparatus. 1 Suction pump, 2 trap, 3 Woulfe's bottle 

 with lime w^ater, 4 Erlenmeyer flask, 5 Woulfe's bottle with lime water, 

 tj and 7 two gas wash bottles with a layer of 40 per cent, sodium hydroxide, 

 and 8 a soda lime tower. By means of a clip on the inlet tube of the tower, 

 the flow of air is regulated through the series of vessels so that the bubbles in 

 bottle 3 can just be counted. 



Method. See that the bottles and flasks are connected in the riglit way so 

 that the air enters by the long tube dipping into the fluid in the bottle. The 

 reaction vessel (No. 4) is a flask fitted with a rubber stopper carrying three 

 tubes. Of these, two tubes are like those of the other flasks. The third tube 

 goes almost to the bottom of the flask and at its upper end bears a fuuiiel and 

 stop-cock. This flask is kept at about 100° C. by immersion in a bath of 

 boiling water. 



First test the apparatus for leaks by running it with the inlet on the tower 

 closed. Now run in the charcoal mixture. (In order to free the charcoal as 

 far as possible from adsorbed COg, it is heated dry and allowed to cool in a 

 desiccator over NaOH.) For our purpose, take 5 gms. of Merck's blood 

 charcoal and suspend it in 50 c.c. of boiled water. Boil the suspension for 

 15 minutes and run it, while still w^arm, into the already warmed reaction 

 chamber. Wash the final grains into the reactioii flask v.ith 50 c.c. of boiling 

 water. Run the pump for a short time to remove the last traces of COn 

 from the charcoal. This may require an hour or so. Now put fresh lime 

 water into bottle 3. Start the pump again. If no turbidity develops in 

 3, the experiment may be begun. If turbidity does develop, proceed as 

 before. 



E.rppriment. Stop the suction and through the funnel add 2 gms. of oxalic 

 acid (dissolved in the minimum amount of water) to the reaction vessel. Start 

 the pump. In the course of a few minutes the lime water in bottle 3 will be 

 quite milky in appearance. It is advisable to run a blank experiment with 

 oxalic acid and 100 c.c. of water but no charcoal in flask 4. 



20. Effect of Capillary-active Substances on the Rate of Sedimentation. 

 Take three test tubes and put about 20 c.c. of water into each. To one tube 



add a few grains of camphor ; to the second a drop of tributyrin. Shake 

 thoroughly and add to all three about 2 gms. of finely ])owdered kaolin. 

 Shake vigorously and leave for about an hour. The kaolin slowlv sinks to 

 the bottom in all the tubes. The camphor and the tributyrin almost doul)le 

 the rate of sedimentation. Repeat the experiment, using powdered charcoal 

 instead of kaolin. Can you explain why the capillary active substances 

 increase the rate of sedimentation of the kaolin and not of the charcoal ? 

 (See Experiment 18.) 



