This is a simple, primitive apparatus that has turned out to be extremely useful in evaluating both detergents and bubble juice. It consists of a plastic bottle whose bottom has been removed. The bottle's mouth is dipped in the solution to test, turned right-side up, and lowered into water.
This allows one to compare bubble lifetimes (if adequate repetitions are performed) in a meaningful way.
It was inspired by an apparatus   that was a matrix of test tubes open on the bottom and top. The test tube matrix was inverted, and the rims dipped in a tray of soap solution. The matrix was turned right-side up and lowered into a tray of water.
Edward's Longevity test apparatusEdit
- Plastic bottle with the bottom cut off. A one pint (half liter) or one quart (one liter) water bottle works fine. Pictured is a one liter gatorade bottle. This is the bubble maker.
- Dipping container. The container needs to be bigger around than the bubble maker (your plastic bottle). Pictured is a one liter glass measuring cup.
- Bubble juice.
- A cup or saucer to hold the bubble juice
Demonstration:EditBubble maker. Plastic bottle with bottom cut off. For the best results, cut out the bottom by going around the rim rather than by cross-cutting at the bottom. This will help the bottle stand level
For the results to be meaningful across sessions, you must record the temperature and humidity.
Ideally, at least 10 repetitions should be performed for each solution in a session.
A control solution that is used in all sessions (such as a simple 10:1 water:detergent mix) is very helpful. It can help calibrate between sessions -- and give you an idea of whether there may be special environmental circumstances in play for any given session.
Care must be taken after each repetition to shake excess water from the bottle -- otherwise your target solution will become more dilute over time.
Care must be taken to take the same amount of time and use the same motion when dipping and lowering the container.
Care must be taken to start the timer at the same point. For instance, start the timer as soon as the container has been completely lowered.
For data to be compared across sessions, you must use a standard water level in the outer container. This creates a standard volume.
In theory, if you could measure the diameter of the bubbles accurately -- you could compare the surface tension of solutions by comparing the volumes of the created bubbles as long as the water level is carefully controlled.
Some thought can be given to the water level to determine what size bubble is most useful for evaluation. It might be possible to compare the 'stretch' that a solution has by measuring the maximum bubble size that can be made with a given apparatus.
This test has a few useful applications:
- comparing longevity of bubbles made with different solutions
- evaluating detergents for optimal dilution range
Evaluating detergents for optimal dilution rangeEdit
Variants and Improvements Edit
The test is not perfect and a reasonable number of repetitions must be performed as there is a fair amount of statistical noise due to both environmental variables (such as floating particles whose distribution may change over time) and performance issues (such as the time taken to dip and place the bottle). Adequate repetitions within a session and repetitions of the session do a very good job of evening out discrepancies.
Due to environmental variation (air quality, humidity, and temperature variations) care must be taken when evaluating the results of different sessions. For this reason, it is useful to use a control solution in all sessions to give a sense of how the session's results compare to others.
Performing multiple repetitions is cumbersome, especially for solutions with good longevity. An apparatus that allowed multiple bubbles to be created simultaneously would be very helpful.
It has been suggested that the test could be made more meaningful by performing the test in an enclosure or by lowering an enclosure when lowering the bubble. There are some pros and cons to such a method. One issue is that the longevity increase can be rather dramatic, making multiple repetitions impractical. The longevity of even mediocre solutions can be extended up to a minute, and only moderately long-lived solutions may create bubbles that last for more than five minutes. Some amount of exposure to the environment does not seem to significantly detract from the meaningfulness of the results and may have some benefit. Exposure to the environment seems to provide some useful test of the the solution's toughness as opposed to a simple gauge of the rate of evaporation.
A method for restoring the film without the need of inversion would be helpful since inverting the container can result in water dripping into the soap solution when dipping if the bottle is not adequately shaken dry.
Thoughts and Discussion Edit
Things to add to the pageEdit
Sample worksheet showing data to be recorded.
Video showing color drain.