old formula... new description!

This is a first!  In all the formulas I have found I have not seen "specific gravity 1.5" listed next to each of the lyes!  I did Google it but didn't find anything that I understood.  Does anyone know what this means?  Thanks in advance for any assistance you can provide!



  • PharmaPharma Member, Pharmacist
    Specific gravity comes from measuring the caustic solutions with a pycnometer and is directly linked to concentration.
  • Pharma, So by looking at the numbers of the KOH and NaOH solutions how do I determine what the approximate numbers are for each of those and the percentage of water in each?
  • ozgirlozgirl Member, PCF student
    edited September 2019
  • ozgirl, thanks!  I did find this page but since I don't have a cosmetic chemistry background, I don't have a clue what all of these things are.  Anything I have read so far hasn't told me anything that I understand.  I just need to know how much NaOH (and KOH) is being used in this formula and how much water would be a part of each solution.  Sorry, for my ignorance but I know what I know and what I don't know I'm willing to try and learn!  :)
  • ozgirlozgirl Member, PCF student

    The calculators and tables might look overwhelming but are pretty are easy to use. If you want an approximate value you can just look up the density that is closest to your value and then read off the concentration in %wt. Or you can use the calculators for a more precise value.  

    In the case of a sodium hydroxide solution at 20oC with a density of 1.5, you can see from the tables that a density of 1.5 gives a concentration between 44 and 48% (closer to 48). The calculator determines that the concentration of sodium hydroxide is 47.31579% on a weight basis. This means that for every 100g of sodium hydroxide solution in your formula you would have 47.31579g of sodium hydroxide and the rest (52.68421g) would be water.

    For a potassium hydroxide solution with a density of 1.5 from the tables you can see that the concentration is between 48 and 50% (closer to 50%) and if you put some values in the calculator you can determine that a  concentration of 49.8 %wt the density is 1.50007.

    Hope this helps. :)

  • Ozgirl - You're the freakin' best!  :blush:
  • PerryPerry Administrator, Professional Chemist
    I love it when people find this forum helpful!!
  • So when I do the math:

    x/4 ~ 47.3/100 = 1.892 (1.9)  with 2.1 H2O  and

    x/20 ~ 49.8/100 = 9.96 (10)  with 10.04 (10) H2O

    making the formula:

    Stearic Acid            50%
    Coconut Acids        12%
    KOH                       10%
    NaOH                     1.9%
    H2O                       26.1% 

    Is this correct?  Looks like it to me!
    The H2O percentage is a little high but it doesn't have glycerin in it and I could add 5%-10% which would put the H2O in the right range also the lyes are in about a 5/1 ratio which is similar to other formulas...

    Thanks again!
  • Actually it is about a 4/1 ratio for the lyes!
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