A couple of months ago, I got an electronic pH meter and began testing the pH of the materials that I use in mixing up bubble "juice". The bottle of glycerine that I was using at the time (labeled as 100% vegetable glycerine) was measured at 5.6. This afternoon, someone wrote to me that their glycerine has a pH of 9.0. Since my measurement of 5.6 gibed with what was reported in a blog entry by respected bubbler Keith Johnson (where he recounted a conversation with the creator or Cricket Hill Powder who suggested that people don't use enough glycerine to balance the alkalinity of the current Dawn line of detergents), I assumed that glycerine was generally about 5.6.
I happened to do a quick test involving Dawn Direct Foam and glycerine (which I will log separately). The results were so different from past detergent/glycerine tests that I decided to test the pH of the glycerine to see if my current glycerine has a different pH than what I have used in the past. The pH measured was 7.2 as measured with an electronic pH meter that is accurate to plus/minus 0.1 and which was just calibrated with fresh buffer solution.
I measured the pH of the two other brands that I have on hand. A mystery-brand gifted to me by Sterling Johnson measured 6.3. Now Brand vegetable glycerine measured 6.3.
If any readers have a reliable way of measuring pH, please post a comment with the glycerine brand and its pH.
If the range of glycerine really is 5.6 to 9.0, it might explain why people report such different results with glycerine. It also might mean that particular glycerines might be a better match for a particular water/detergent combination. If one's water is alkaline, an acidic glycerine might be called for.
But, it isn't yet clear if there is that much variation. My earlier 5.6 reading may have been due to faulty calibration. The meter was new and I was inexperienced with it when the reading was made.
[NOTE: Sept. 26. I was just contacted by the person who had "reported" a glycerine pH of 9.0. It turns out that I mis-interpreted something that he wrote. His glycerine is about 6.0. So the reported variation is only 6.0 to 7.3, which is not as large a spread and may not be significant where bubble solutions are concerned.]