# Homework Help: Collecting pure gas bubbles

1. Jan 10, 2010

### olmec

1. The problem statement, all variables and given/known data
I am attempting to collect bubbles that are being produced under the water surface.

The bubbles are natural gas, lighter than air

I can collect the by bubbles by directing them into a funnel and up a hose and into an airtight collection vessel.

I want to know what pressure is required before the air in the pipes and vessel will be expelled back out the funnel, through the water and back to the air. Mouth of the funnel is several centimetres under the surface of the water.

Can anyone think of a better way of doing this without pumps etc.

Last edited: Jan 10, 2010
2. Jan 10, 2010

### ideasrule

Why not fill a jar with water, invert it and place its top under water, and direct the propane into the jar? The water will be pushed out and the propane will float to the top.

3. Jan 10, 2010

### olmec

Yes, this does work. I have done this to test the burn-ability of the bubbles and confirm they are natural gas.

I then moved on to a closed system with a collector drum filled with water and a funnel suspended above the bubbles (under the water surface) because the drum and water was only slightly higher, the water stayed in the collector until the gas replaced it. I had pure gas to burn.

Because the bubbles are small, collection is slow. Also, the location is not easily accessible so I wanted to have a long hose from the source up the cliff to the collector at the top for better access.

I am now thinking of attaching a collection pipe directly to the rock where the bubbles emerge and seal it so bubbles have to go up the tube to collector.

Would be nice to have a way of knowing when the collector was full and have only gas (no air). Your approach (and my first attempt) worked well to ensure only gas and when the collector was light (not filled with water) then it was full.