“With soda walks faster, right?”

   Although Mrs. Rosa did not mention, some women use caustic soda or sodium hydroxide in the ash soap making too, as was the case of Mrs. Anésia’s mother: “My mother used the two, right? Soda and dicuada. That she put a little of each one. With soda it walks faster, right? It makes the soap faster. My mother made this way. She used soda and ash, the two. She said that it was to make it walks quickly. She used minus soda, right?”

caustic soda

   According to Mrs. Anésia´s mother the advantage of using soda in the soap´s making is that it “walks faster”, “it makes the soap faster”, “it walks quickly”, it accelerates the rate of saponification reactions. Generally, catalysts accelerate chemical reactions but this is not the case of adding sodium hydroxide as it is consumed in the reaction with the fatty acids, just like potassium carbonate and produces soap too. Why does its reaction “walks faster”?

   A condition for the chemical reactions to occur is that reactants must collide with each other with an amount of sufficient energy to destabilize them and provoke rearrangements of the atoms with formation of new chemical species, the reaction products. This energetic condition varies from one reaction to another and is called “activation energy”.  In the case of the reactions involving sodium hydroxide in the ash soap´s production, the activation energy must be lower in comparison with that involving potassium carbonate. Thus, “with the soda walks faster”, “it makes the soap faster”, the reactions occur more rapidly due to the lower energetic demand.

   Mrs. Anésia mentioned that her mother created 12 sons and never bought a soap. It means that the cleaning and hygiene of her family was done using the ash soap that took soda on its making. Their colleagues, however, showed to be against the soda´s use:

Rosa: Ok, I don´t use soda at all. I put only the dicuada. If soda is put therein it doesn´t serve for people to wash the head, right?

Aparecida: Right, with the dicuada. And you can use it for burns, can use it for everything with no problem, right? And with the soda there can be no longer use, because the soda affect, you know? The skin. It isn´t good the soda.

   The argument of Mrs. Rosa is that when soda is added in the making the resulting soap can be no longer used for washing the head. Mrs. Aparecida mentioned that the soda can harm the skin, but if the soap is made only with dicuada it can be used “for everything with no problem”, observing the soaps’ use on epithelial burns treatment also. Mrs. Rosa said next that “there´s a lot of people that look for”, “to give it to chicken, golgo thing, of chicken, that is also good”, but “if put soda there has no longer use for medicine”. She referred to a chicken disease and to people’s search for healing it with the ash soap.

   The caustic soda is a highly corrosive substance, which can irritate the skin and eyes provoking sores in the nasal cavity and permanent damage. The potassium carbonate has similar effects, but milder in comparison with caustic soda (Patnaik, 2002, p. 186).  Then, why the soap made with the dicuada does not irritate the skin and the scalp and can be used in burns or a remedy for hens? How to explain the fact that Mrs. Anésia´s mother used the soap prepared with dicuada and soda, “a little of each one”, and used it to clean 12 children and did not damage none of them? They did not notice that while they were talking?

NaOH grains

Caustic soda

   We have seen that the mixture of the ingredients in the ash soap´s making is done with attention, especially closer to the “point” or the end of saponification. In the soap´s making, the women seek to adjust the relative amounts of dicuada and fat in order to do not let “pass” or “miss” any of the two, none must be above or below the amount required by the “point”, the stoichiometry of the reactions. Thus, if the control of the process is well done, there will be no excess of dicuada, soda or fat in the final product. These reactants will consume each other in the chemical reactions and their molecules will be modified, transformed in new substances with distinct properties.

   Wasn´t Mrs. Rosa that said: “Where is the fat in the pot?”, suggesting its disappearance  by the dicuada´s action. Wasn´t Mrs. Aparecida that mentioned that the fat “weakens” the dicuada? In the same way, isn´t it the same for the soda? Their positions about the use of this substance in the soap´s making suggest that they are seeing its action differently from that of dicuada. Perhaps they are trapped to the tradition or are afraid to use caustic soda because its dangerousness. Did they not notice that the mother of Mrs. Anésia created 12 sons using a soap that took caustic soda in its making? Similar to the ash soap, handcraft soaps in general are more valued than those industrially made due to the greater control of the relative amounts between the reactants in the production processes. These soaps are, therefore, less aggressive to skin.

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Back to: “Where is the fat in the pot?”


Patnaik, P. (2002). Harmful Properties of chemical substances. V. 1. Belo Horizonte: Ergo.

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