until the water in the beaker is at the same level as the water in the bottle; then the screw clamp is closed. Empty the beaker, and return it to the position shown in Fig. 23. Now open the screw clamp and apply a gentle heat to the potassium chlorate. Oxygen is evolved and forces the water from the bottle into the beaker. Gradually increase the heat, and continue the heating until all the oxygen has been expelled. Let the apparatus stand until it has acquired room temperature, care being taken that the glass jet is kept below the surface of the water in the beaker (why?). Now bring the level of the water in the beaker to that of the water left in the bottle, and, while holding it in this position, close the screw clamp (why?). Carefully measure the water in the beaker; also take the readings of the thermometer and the barometer. Disconnect the tube A, and carefully reweigh the tube and its contents. Insert the values in the following table:

Weight of tube A + the potassium chlorate.

Weight of tube A + the potassium chloride

Volume of water in beaker = volume of oxygen evolved
Temperature of water
Barometric reading .

From your results calculate (1) the percentage of oxygen in potassium chlorate, and (2) the weight of 1 liter of oxygen under standard conditions. Compare your results with those given in the text.

If sufficient heat has not been applied to expel all the oxygen from the potassium chlorate, incorrect results, of course, would be obtained for the percentage of oxygen present. This would have no effect, however, upon the determination of the weight of 1 liter of the gas. It is well, therefore, after the tube A and the residue have been accurately weighed, to reheat the tube and reweigh. This process should be repeated until the tube and contents suffer no loss of weight on heating.

CHAPTER IV

WATER AND HYDROGEN PEROXIDE

32. Distillation. Connect a 500-cc. flask A with a Liebig condenser B (obtained from the general storeroom), as shown in Fig. 24. The tube C is connected with the water pipe by means of rubber tubing, and a current of cold water is allowed to flow through the outer tube of the condenser. Why is cold water admitted at C rather than at D? Half fill the flask with hy

drant water and boil till 100 cc. or more of liquid has collected in E, the receiver. Compare the distillate (distilled water) with the hydrant water in appearance and taste. To what is the difference due? Interrupt the process of distilla

FIG. 24

tion and add a few crystals of a highly colored salt (potassium permanganate) to the water in the distilling-flask. Continue the distillation of the water. Is the distillate colored? Place 4 or 5 drops of the distilled water on a watch glass and evaporate. Is there any residue? Repeat, using hydrant water. Why is distilled water used in the laboratory?

33. Filtration. a. To about 25 cc. of water in a beaker add 1 or 2 cc. of ammonia water and stir. Note the odor of the solution. Add as much bone black or powdered charcoal as you can pile on a five-cent piece, and thoroughly stir. Filter