Experiment 7. To make water balloons.
Close one end of the No. 2 tube in the blowpipe flame again and while it is still hot blow carefully into the open end until you have a bulb about ½ inch in diameter (Fig. 12). Now let it cool. Make a scratch with the file about ¼ inch from the bulb, break the tube at this point (Fig. 13), and smooth the rough edge.
FIG. 14
THE BALLOON SINKS AND RISES
Put the bulb in a tumbler of water. Does it float? If not, make another balloon with a larger bulb.