Sodium Silicate Testing Procedure | Alkaline Silicates Testing Method in Soap

This method determines the Alkaline Silicates ( Sodium Silicates ) in the a soaps sample.

Scope:- This testing procedure applicable to all Soaps and soaps Products and containing synthetic detergents.

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Platinum evaporating dish, capacity 100 ml.

Platinum crucible 30 ml.

Watch glasses. 

Filter paper, ash-less grade  small side 30 ml.


Hydrochloric Acid (AR,LR) specific Gravity 1.190 

Hydrofluoric Acid (A.R) Grade 48% HF.

Sulfuric Acid (AR, LR) specific Gravity 1.840

Procedure Sodium silicate testing 

(A) When the sample contains no mineral matter  that is insoluble in Water.

1.0 Weight a size of sample such that it will contain not more then 0.20 gm of SiO2 into a platinum evaporating dish and ignite over a Muffle furnace or a Burner below a dull red heat ( 360°C  - 450°C ) until the mass is charred. Add distilled water and filter by a filter paper. Wash the dish and residue on the filter paper 2-3 time with distilled water so as to extract all water soluble material.

2.0 Return the filter paper containing the charred residue to the platinum dish and continue the ignition at a bright red heat (850°C - 950°C) until all carbon is removed. Unite the residue and all of the water extract and neutralize so carefully with a Hydrochloric acid and then add form 5.0 - 10.0 ml of HCl in excess. keep the dish covered with a watch glass during this addition to prevent loss from spattering.

3.0 Evaporate to dryness on a steam or water bath or on a hot plate at a temperature not exceeding 120°C. Cool the residue sample and moisten with HCl let stand 5 - 10 minutes and then break up all lumps with a stirring rod.

4.0 Add 25 ml of hot distilled water to the residue and heat for a few minutes and filter through a small ash-less filter paper. Repeat the above treatment, C, 3 and 4, beginning with ''Evaporator to dryness .........'' Filter by a second filter paper.

5.0 Place the two filter papers in a tared platinum crucible and ignite carefully and first at a low temperature until the paper is consumed and then over a burner or in a muffle at a bright red heat (850°C - 950°C). Cool to room temp. in a desiccator and weight. Repeat until constant weight is obtained.

Alkaline Silicates Testing Method in Soap

6.0 For the most accurate result moisten the weighed contents of the crucible with water. Add 10.0 ml of Hydrofluoric Acid ,4.0 drops of Sulfuric Acid (H2SO4) and evaporate to dryness over a low flame. Ignite as directed in paragraph 5.0. Cool to room temp. in a desiccator and weight.

(B) When the sample contains mineral matter insoluble insoluble in water or when a determination of the highest accuracy is not required.

1.0  Use a portion of the solution after titrating the matter insoluble in alcohol but soluble in water, such that it will contain not more than 0.2 gm of SiO2.

2.0 Add 5 to 10 ml of HCL and Procced form here on as directed in (A) beginning with paragraph 3.0.


a. When SiO2 is weighed.

Sodium silicate (1Na2o : 3.25 SiO2) % = Weight of residue (from C,a 5)X131.8 / Weight of Sample

b. When SiO2 is Volatilized With Hydrofluoric Acid.

Sodium silicate (1NaO:3025SiO2)% = (W1 - W2)X131.8 / Weight of sample


W1 = weight of crucible and contents from C (A) 5

W2 = weight of crucible and contents from C (A) 6

Determination Of Sodium Chloride in Glycerin 

Sodium Chloride is not usually determination in a crude glycerin. This method for its determination os included for convenience and completeness.

The end-point in the sodium chloride titration may be seen more easily if illumination is furnished by a Mazda lamp of suitable size screened by a Wratten safe-light filter no. 00  


1.0 Volumetric Flask 100 ml

2.0 Erlenmeyer Flask 250 ml

3.0 Evaporating dish 

4.0 Muffle furnace 

5.0  Ash less filter paper


1.0 Distilled water

2.0 0.25N NaOH and Sulfuric Acid solution  

3.0 Potassium chromate indicator 

4.0 0.1N Silver nitrate solution

Procedure:- Weight Accurately 2.0 to 5.0 gm. of well mixed sample into a tared platinum dish. Dry to constant weight in an air oven at 130°C. or over an Argand burner or in a muffle below a dull red heat (500 - 550°C ) and cool to room temp. in a desiccator.

Dissolve the ash in 25 ml hot distilled water. Cool to room temp. and into the sample in 100 ml volumetric flask  make up to 100 ml with distilled water. And pipet 50 ml into a 250 ml Erlenmeyer flask. Add a few drops of phenolphathalein indicator solution and adjust neutrality with 0.25N NaOH and H2SO4 leaving the solution and adjust acid. Add 1.0 ml of potassium chromate indicator solution and titrate to the first permanent reddish tinge with 0.1N AgNO3.

Sodium chloride % = Titration X normality X 5.85 / 0.5 X weight of sample used in 

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