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UPDATE IN PROGRESS -- I need to try a new test protocol to see if it will be more efficient for exploring this.


As I read through various people's experiments and recipes and experiment myself with my own formulas, it is clear that you can't just substitute one detergent for another. So, I have been trying to figure out a way that one can find a way of comparing the relative amount of surfactants in a detergent which should at least help with finding the dilution to use as a point of departure. I tried dehydrating a few detergents -- and there is some promise but it probably is not a very accurate comparison because there is no guarantee that the amount of surfactant hidden in the other dry ingredients is going to be similar across the detergents.


So, it occurred to me that it might be worth measuring the minimum amount of detergent required to create a stable bubble. Perhaps this will be a better indicator of the amount of surfactant in a detergent. I started by counting the number of drops that needed to be added to a given amount of water -- but was confounded that the number of drops was similar across a number of detergents whose strengths seem pretty difference. After a bit of thinking, I realized that the surface tension and viscosity of the detergents might influence the size and weight of the drops. A bit of experimenting showed this to be true. And it also showed that the amount per drop wasn't consistent enough to be used as a precise measure.


While the experiment itself failed, I was shocked by how little detergent was required to form a stable bubble (using the longevity test apparatur) and how long they lasted. At dilutions on the order of 75 parts water to 1 part detergent, bubbles lasting a minute were created. By contrast, an 8-to-1 dilution with the same detergent lasts only 10 seconds!


I then launched into the time-consuming test of taking a fixed weight of water (50 grams) and adding detergent in .1 gram increments. And after each addition doing a test to see if a bubble could be formed using the longevity test apparatus. It took a while before I realized that after each addition, I needed to try 3 times to form a bubble. These tests are indicating that only between 0.3 grams to 0.5 grams are needed for 50 grams of water when using Dawn Ultra. At these concentrations the bubbles last more than 30 seconds (and as long as a minute) but are almost transparent. Doubling the detergent seems to improve the color considerably.


I haven't done enough iterations of the other detergents to share their results. That should happen in the next few days and will give me an idea if this is a useful measure.


It will also be useful to plot the longevity as a function of the amount of detergent since it is clear that there are some interesting non-linearities.


It may be useful to do the tests with more water so that more detergent is needed which will reduce the amount of error introduced by my scale's (lack of) precision.


NOTE (6/24/2010): I will update this post after I try out a new method of doing the dilution -- the current method is too-consuming. Once I have some new data, I will update this. In the meantime, I am continuing to find interesting behavior and non-linearities. Very dilute solutions seem to last considerably longer than less dilute solutions BUT they are more difficult to bubble successfully. There is clearly some tension between maximizing bubble life and ease of bubbling.