I found a formula I would like to use as comparison.  It lists:

550 kgs. Potash Lye 50 degrees B
40 kgs. Soda Lye 45 degrees B

I did some research and have a basic idea about Specific Gravity, water percentage and lye percentage but really don't have a clue how to calculate this!  Any assistance you can provide will be greatly appreciated!



  • PharmaPharma Member, Pharmacist
    What exactly do you want to calculate?
    To me it looks like no calculation is needed. Take 550 kg of potash lye (whatever 50 stands for) and mix with 40 kg of soda lye (again, no clue what 45 means). Dunno if it's important to hold it at B degrees :blush: .
  • My understanding is that it is referring to a solution of lye and I need to determine the amount of water and the amount of lye in each of the two ingredients listed.  My keyboard doesn't have a "degree" symbol but it is referring to Potash lye which weighs 550 kilograms and is a solution used at the amount of 50 degree Baume.  Yes, it is an old formula and if I could figure it out myself, I would but so far I haven't been able to get it!
  • "The Baumé scale is a pair of hydrometer scales developed by French pharmacist Antoine Baumé in 1768 to measure density of various liquids. The unit of the Baumé scale has been notated variously as degrees Baumé, B°, Bé° and simply Baumé (the accent is not always present)." from Wikipedia...
  • PharmaPharma Member, Pharmacist
    Okay, now I get it! I was already wondering what your title meant... looks French, sounds French but doesn't mean anything in French (unless it's patois).
    So, according to Wiki, you calculate specific gravity of the required solutions as follows: 145/(145-50)=~1.526 for potash and 145/(145-45)=1.45 for soda.
    And that's about what you can calculate. Now you need a conversion table to get the concentrations or you do a concentration curve and determine it yourself.
  • Pharma, thanks for your input but now I'm even more confused!  I have tried to find info on Conversion Tables and Concentration Curve but didn't find anything I understand.

    I took the formula from the Thomssen 1937 book as written and put it through an Amount to Percentage Calculator.

    Since the number for the oil phase total about 67% and the ratio between the two "oils" is what I need, I still need to figure out the actual amount of lye and water for the NaOH and KOH.  Does this make it easier to calculate?
  • PharmaPharma Member, Pharmacist
    edited August 2019
    Why didn't you tell us right away that you're going to make soap?
    You ARE going to make soap, right?
    BTW there's a 35 B° in that table whereas your first post says 45 B°.
    You could simply re-calculate the amount needed for the degree of saponification you're looking for by estimating based on saponification numbers. Since 45 and 50 won't be that different (you're going to experience a difference anyway since then and now changed more than a few things), you could simply use a ratio of 55:4?
    Or you figure out how to use google and then get the following answers:
    HERE's a table for NaOH aka soda lye = 42.07% solution at 20°C.
    HERE's the one for KOH aka potash lye = ~51.6% solution at 20°C.
    Need more help calculating or does that suffice?
  • Sorry Pharma,

    Yes, I am going to make shaving soap and the table is correct with 35 degrees Baume!  (Don't get old!)

    Yes, I could (and will) recalculate the SAP numbers for this formula and see what I come up with, but what I am looking for is what they came up with, not only the numbers but the ratio of the two hydroxides together!  (is it a 5/1 ratio or another ratio?)   Also, how large is their water phase and what is their superfat percentage?

    So , it is:

    1.98% (almost 2%) of NaOH at 35 degrees Baume
    27.228% (almost 27.25%) of KOH at 50 degrees Baume

    Sorry, I am clueless at this point but if you can assist me with the rest of the calculation, I can learn from it and others here will have this available if they need it!  I really appreciate your assistance!!!!!
  • David08848David08848 Member
    edited August 2019
    Pharma et al,

    I found a calculation I made years ago but I am not sure it is correct.  When I put these numbers through a lye calculator both KOH and NaOH numbers are lower than what this formula shows:

    35 Baume = 28.83% solution = 11.53 lbs. lye and 28.47 lbs. H2O

    50 Baume = 49.40% solution = 271.70 lbs. lye and 278.30 lbs H2O

    This formula changed from Baume solution percentages to lye amounts plus total H2O looks like this with the original listing turned into a formula based on 100% on the right:

    300 lbs.          Coconut Oil               14.85%

    11.53 lbs.        NaOH                         2.32%

    271.70 lbs.     KOH                           13.45%

    80 lbs             Glycerin                     3.96%

    1050 lbs.        Stearic Acid                51.21%

    306.77            H2O                           14.96%     ______________________________________________

    2020                                                   100%

    I am not sure whether the original calculations of the Baume ingredients are correct.  Would you kindly look it over and see if is it correct?


  • PharmaPharma Member, Pharmacist
    edited August 2019
    Conversion of °B seems to be not fully regulated but depends a bit on the author/country and is also temperature dependent. But it should be just minor differences and still give you a fair idea on what's happening.

    Let's assume you were to use the following amounts in mM (for me, it's simpler to calculate with that for defined molecules):
    NaOH: 58 mM
    KOH: 240 mM
    Stearic acid: 180 mM
    Water is in excess and glycerol doesn't contribute to any reaction whereas coconut oil can not be calculated in mol but we'll use saponification value afterwards.
    For simplicity, we first react NaOH with stearic acid so we use it up completely. Then we use KOH to neutralise the remaining stearic acid. This leaves us with 118 mM excess KOH. Since saponification values are in mg alkali per g fat, I do a switch between % and g per 100 g product: In other words, 49,17% of the added KOH is left for saponification of coconut oil = 6.61% total weight KOH. 14.84 g (for 100g product) coconut oil requires ~3.8 g KOH for 100% saponification. In the end, you have 2.81% excess KOH or a very alkaline soap!
    This excess might be a result of quality or conversion inaccuracy. I'd assume your recipe is for a fully saponified product and if I were you, I'd do the proper maths with your products for a perfect 100%. Depending on your requirements/options/visions, you might want to use a tick too much or not enough alkali as it's common practice in soap making.
    If you want to keep the same "feel" of your recipe, it's a 20:80 ratio (on a molar basis) of NaOH/KOH or in other terms a 20:80 mixture of soda soap to potash soap (again, on a molecular basis). This allows for a simpler calculation with just one of the alkalis and you calculate the alkali ratio last. Given that weight differences between Na and K in a soap molecule are minor, mixing 20 parts of soda soap with 80 parts potash soap (on a weight basis this time!) should give a product fairly similar to what you're looking for. It might be easier, case you do a hot process, to do a batch of soda and potash soap apart and mix them afterwards (by melting them together). This gives you more flexibility in finding the right consistency/foaming/etc. because you can successively add more of one or the other whereas mixing all in the beginning requires you to run an entire batch for every ratio you want to try ;) .

    Hope this helped!
  • Thank you.  When I am trying to create a new product I go out there and look for any formulation that is available for that kind of product.  Usually, when I find several formulas then often patterns emerge.  Specifically, I am looking a shaving soap formula and I have found most of them are in either old soapmaking books or cosmetic chemistry books.  Shaving Cream formulas were quite numerous and it was not difficult to find several formulas that have phases with similar sizes and similar ingredients.  Shaving Soap formulas, however, are not quite as readily available and many of them are from the early 1900's rather than the mid 1900's and as such they mostly contain KOH and NaOH with Baume numbers listed and many of these are also made in soap crutchers rather than using a cold or hot process.  Nonetheless, it is a formula that I can learn something from. 

    Yes, I can use the amount of the oil phase and calculate the SAP values for NaOH and KOH with them in whatever ratio I wish to try but I want to see what ratios they used and why!  For me, it has been easier to work with several sample formulas to enable me to at least be somewhere in the ballpark where the numbers are concerned!  This is why I want to be able to calculate the formulas I have found to see what direction they are using and what ratios of lyes as well as the size of water and oil phases. From there I always do what you have suggested and make several batches, testing each for direction I need to go and work from there. So hopefully you better understand my process and my needs.  Thanks again for you help!  Time to look for some "mid-century modern" 1900's formulas!

  • PharmaPharma Member, Pharmacist
    Do you know "Henleys Twentieth Century Book of Recipes, Formulas and Processes"?
    A real treasure filled with old formulas and it's readily available online as PDF (for free if you know where to look)!
  • Download it but it only had one formula and that was for shaving soap fragrance!  ;)
  • ...and, of course, the US Patent and International Patent old friends! :)
Sign In or Register to comment.