Determination of Solubility of Wool in Alkali Textiles Material

This standard prescribes a method for determining the solubility of wool in alkali applicable to ail-wool textiles in any form such as fiber, yarn and fabrics.


The test should be carried out in prevailing room conditions


  • Water bath – maintained at temperature 65° ± 0.5°C
  • Stoppered conical flask- 250 ml capacity – 3 NO.
  • Sintered glass filtering crucibles with watch glass – 3 No.
  • Filter Paper thimbles
  • Hot air Oven  – 105 ± 3°C
  • Desiccators -250 mm
  • Soxhlet extraction apparatus.
  • Extraction Flask- 250 ml – 3 NO.
  • Thermometer – Up to 100°C


  • Light Petroleum ether – boiling point 40 24°-60°C
  • Sodium hydroxide 0.1N
  • Acetic acid – 1 %
  • Pyridine solution – 0.5 percent
  • Phenolphthalein indicator


  • From the test specimen, take about 10 of representative sample.
  • Extract the representative sample in a Soxhlet apparatus with petroleum ether for one hour at a minimum rate of six cycles per hour.
  • Allow the petroleum ether to evaporate from the test specimen for about 20-30 minutes.

  • From the representative sample, take about I g of test specimen. Extract it with cold water with liquor to material ratio of 50: 1 for half an hour shaking the flask occasionally and determine the pH of the extract. If the pH of the water extract is less than 4.0, determine the acid content by the method given in procedure B, Otherwise continue with procedure A


Determination of dry weight of test specimen

  • From the extracted representative sample, take one test specimen weighing 1.0 gm.
  • Dry it in a weighing bottle at 105°C for three hours.
  • Stopper the bottle and cool it in a Desiccator and weigh as W1.
  • Remove the test specimen and weigh the weighing bottle, taking as W2.

Calculate the dry weight of test specimen as follows 

Dry weight of specimen: –   W1 – W2

Determination of alkali solubility

  • Pour 100 ml of 0.1N sodium hydroxide in a conical flask. Stopper it loosely and fix it in water bath previously maintained at 65 ± 0.5°C.
  • When the temperature of sodium hydroxide in flask reaches 65°C, introduce extracted test specimen weighing about 1.0 g into the flask.
  • Replace the stopper tightly and shake the flask gently for two minutes.
  • Replace the flask in the water bath and continue shaking the flask at successive intervals of 15, 30 and 45 minutes.
  • After 60 minutes, transfer the contents of flask to a weighed filtering crucible and drain by suction.
  • Wash the flask with water and collect the washings in the filtering crucible, draining between each wash.
  • Fill the crucible with acetic acid solution, allow it to stand for 1 minute and drain the liquid by suction. Repeat this twice.
  • Again wash the residue six times with distilled water draining completely between each wash.
  • Shift the crucible and its contents to hot air oven and dry at a temperature of 105°C for three hours.
  • Stopper the crucible or cover it with a watch glass.
  • Cool it in Desiccators and weigh. Repeat the operation of drying and weighing until constant weight is obtained.


  • Place two test specimen each weighing 2 g in separate conical flasks.
  • Pour 100 ml of pyridine solution into each flask.
  • Stopper the flasks mechanically for one hour.
  • After one hour, filter the liquid in a separate conical flask, thus separating fibrous material.
  • Pipette out 50 ml of each filtrate in separate conical flasks
  • Add 3- 5 drops of phenolphthalein indicator to each flask.
  • Titrate separately with 0.1N sodium hydroxide till a faint or light pink color appears.

Calculate the weight of acid as the percentage of the dry weight of each specimen by the following formula:

a    = v * k * n / W1
Where, a = acid content, percent
v = volume in ml, of sodium hydroxide required to neutralize 50 ml of pyridine solution.
k = constant
n = normality of sodium hydroxide solution.
W1 = dry weight of 1 gm of specimen

Note: – The constant has the following values:
Acid Value

Sulphuric acid 4.9

Formic acid 4.6

Acetic acid 6.0


1.If the sample does not contain acid (that is, if the pH is 4.0 or greater than 4.0), calculate the alkali solubility of each test specimen by the following formula:

Solubility in alkali, percent =      W1 – W2 x 100 / W1

               W1 = dry weight of test specimen
W2 = dry weight of the residue.

2. If the sample contains acid ( that is, if pH is less than 4.0) calculate the alkali solubility of each test specimen by the following formula:

Solubility in alkali, percent = 100 [100(W1 –W2) – a / W1 100 – a

W1 – dry weight of the test specimen,

W2 = dry weight of the residue, and

  a = percentage of acid.

REFERANCE: – IS 3429- 1966 – methods of determination of solubility of wool in alkali.

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