Inflate a balloon to prestretch its wall, then deflate it.
Press all air out of it. Weigh the empty balloon. Inflate the
balloon with the gas of interest. Tie the balloon by stretching
and making a knot. Loosely attach a string to the balloon.
Let the balloon float in air. Adjust the weight of balloon by
adding to or cutting off portions of the string so that the
balloon neither rises nor sinks. Untie the string and weigh it.
Fasten a tape vertically on the outside of a 1000-mL beaker.
Collect the gas by puncturing the balloon under water inside
the inverted beaker filled with water in a bucket. After
equalizing the water levels inside and outside the beaker by
raising or lowering the beaker, mark the water level on the
tape and record the volume of the gas. A typical experiment
yields a volume of about 600 mL. Record the barometric
pressure and temperature.