Soap: Composition and Types | Cleansing Agents | Home Science

After reading this article you will learn about:- 1. Meaning of a Soap 2. Composition of a Soap 3. Properties 4. Action 5. Manufacture 6. Types.

Meaning of a Soap:

Soap is the best cleansing agent for washing of fabrics from a long period of time. The discovery of soap has brought a revolutionary change in the field of laundry. It is recorded that the soap industry flourished in Italy, Spain, and France during the eighth and ninth centuries.

The chemical processes of soap making was discovered by two French men, Chervil and Leblanc in the year 1800. Today’s soap markers have kept the original formula and have improved the method of preparing soap. In the beginning of 19th century small soap factories were established. Now it become one of the big industries in India as well as all over the world. A varieties of soaps are manufactured as per the changing demands of the consumers.

Composition of a Soap:

Chemically, soaps may be termed as sodium salts. Soaps are quite complicated in their composition because salts of more than one fatty acids are present in a soap. The two chief materials required in the making of soap are fats and alkalis. Some other materials are mixed to increase the cleansing action and to give them perfect shape.


The materials used for the preparation of soap are:

1. Fats and Oils

2. Alkalis

3. Water


4. Sodium silicate

5. Starch

6. Soapstone’s

7. Salt


8. Resin

9. Mineral oils

10. Disinfectants

11. Auxiliary substances like colour perfume Brighteners etc.

1. Fats and Oils:

These are the chief materials for soap making. Fat and oil, the triglycerides are hydrolysable by alkali and the process is called as saponification by which soap is produced. In soap making both animal and vegetable fats are used. The animal fats are tallow and Lard and the vegetable fats are different types of oils like Coconut oil, Cotton Seed oil, Palmoil, Castor oil, ground nut oil etc., which are used in soap.

In most cases Mahua oil is used in making laundry soap as it is cheap. Tallow and Lard are mixed with coconut oil or other oils to produce soap. Because good soft soaps can be made by a combination of Tallow and coconut oil. Animal fats are generally used for the preparation of laundry soap and vegetable oils are used for bathing soap. In order to improve the quality of soap and to make the soap less expensive, a mixture of animal fat and various vegetable oil are mixed for the preparation of soap in many soap factories.

2. Alkalis:

Caustic Soda, Caustic Potash, Sodium Carbonate Potassium Carbonate are the alkalies used in the preparation of soap. The chief alkali used in soap making by most of the soap factories is caustic soda. Caustic potash is used for the preparation of soft soaps. The ordinary household laundry soaps are prepared from caustic soda. The alkalies in blocks are used in soap making.

3. Water:

Water is required for the preparation of all types of soaps but the percentage varies with different soaps.

4. Sodium Silicate:

This is generally alkaline in nature, which possess good detergent or cleansing properties. Neutral silicate containing a smaller proportion of soda is used. The proportion varying from 5% to 25%.

5. Starch:

Starch has the property to combine with water. It forms a gelatinous substance in the presence of alkalies which is soluble. So it is added to make the soap firm. Generally 2% of starch is safely used in hot process and up to 20% in cold process of soap making.

6. Soap stone:

This is used as a filling agent for the preparation of soap. Soap stone or French chalk can be used up to an extent of 15 to 20%. But it has no detergent properties. Soap stone is not used in good quality soap.

7. Salt:

Salt is used for graining the soap out from a mixture of oils and alkalies. The usual proportion is 100 parts of oil to 12 ½ parts of salt.

8. Resin:

Resin and naphthenic acid may also be added to improve the effectiveness of soap. Their presence makes the soap yellow. By the addition of Resin the cost of soap is reduced. It should not be more than 15 to 20% of fat. The disadvantage is that it changes the white fabric to yellow colour.

9. Mineral oils:

Some mineral oil like paraffin oil or turpentine oil may be added to enhance the cleansing action of soap. It also helps in removing grease and stain.


Disinfectants like carbolic acid may be used for the preparation of disinfectant soap. It can kill the germs and bacteries.

11. Auxiliary Materials:

Some antioxidants like sodium silicate, Sodium thiosulphate are also used for the preparation of soap as soap is sometime susceptible to oxidation. Colours are added to soap in order to make it more attractive. Generally aniline dyes .which are soluble in water are used to colour the soap.

Perfumes are also added to make them more attractive for customers. Toilet soaps contain more perfume than the laundry soaps. Some optical brighteners are also added to soap In order to increase the white appearance of cloth. Without bleaching or applying blueing agent to white fabrics, they can be made brighter only by washing with soap.

Properties of a Good Laundry Soap:

A good laundry soap specially suitable for washing clothes should be used for cleaning.

The quality of a soap can be judged in the following way:

1. A good soap should contain 30% water and 61 to 64% combined fatly acids.

2. It should be free from resins.

3. It should be readily soluble in water and also give a good lather.

4. The soap should be of a clear pale colour.

5. The soap should feel firm when pressed with the finger.

6. Good laundry soap dries with firm surface on storage. Soap that develops white crystals on the surface should not be used as this shows the presence of excessive alkalies.

Action of a Soap:

1. Soap makes the penetration of water into the fabric easier.

2. It helps to break down the surface tension of the fabric so that soap solution will wet the fabric more readily than ordinary water.

3. The soap solution breaks up the grease into small particles which come off the fabric and float in the solution. It also attracts the dust particles. So the fabric is made free from both dust and grease.

4. When soap comes in contact with water, alkali is liberated by the action of water on soap and helps the emulsification of greasy dirt. Thus it facilitates the washing process.

5. Most of the non-greasy dirt is removed in steeping by the pedesis of wafer or the movement of water particles. Soap in water increases the pedisis and thus quickens the removal of non-greasy dirt.

Manufacture of a Soap:

The usual method of soap making is by the process of saponification. When fat is mixed with alkali it is broken up into fatty acids and glycerin. The hydrolysis of fats and oils can be brought about by heating them with water, acids or alkalies. When fatly acid are hydrolyzed with alkalies, soaps are formed. This process or reaction is called saponification.

There are two processes of manufacturing of soap:

(1) Boiling or hot process

(2) Cold process.

1. Boiling Process:

This is also known as kettle process as it is prepared in a soap Kettle.

1. Oil or molten fat is taken in soap kettle.

2. Slightly excess amount of alkali is added to it.

3. The mixture is boiled by passing steam directly into the kettle.

4. The boiling with steam is continued till all the oil or fat is completely saponified. More caustic soda solution is added at intervals and the process of boiling is continued for two to three days.

5. When a homogeneous pasty mass results, sodium chloride is added in small quantities to the boiling mass.

6. The contents of the soap pan are soap, glycerin, excess amount of caustic soda and impurities. Brine solution is added which helps in separating the soap out and this forms a layer on the top. The liquid under this layer consists of glycerin and impurities. This is known as “spentlye”.

7. “Spentlye” is taken out and glycerin is stored after making proper distillation.

8. The soap layer is then mixed with water and boiled which is converted into a paste. More caustic soda is added till saponification is complete.

9. The soap is then boiled with steam and left to stand until four layers are formed. The top player is just a forth, the second layer is the genuine soap, the third layer is an impure dark coloured soap and the fourth layer is some alka line liquid.

10. The genuine soap is passed into another pan, colours, perfumes, and other substances are added. Then the soap is moulded and cut or made into flakes or powders.

2. Cold Process:

This is a simple and quick method of soap making:

1. In this process the molten fat or oil is mixed with required amount of alkali and is mechanically stirred till soap begins to set. The heat given off by the mixture (oil + caustic soda or caustic potash) is sufficient to carry out the process of saponification which takes at least a day or two to be completed. In this method it is necessary to take the correct proportion of the ingredients.

2. When the soap begins to set, required amount of colour, and perfume are added and the thick mass is poured into frames and allowed to remain their for 2 – 3 days till the mass cools and becomes solid.

3. The soap is then removed in the form of a block which is cut into different shapes and sizes.

The hot process is more economical than the cold process which yields pure product because impurities and excess alkalies are completely removed.

Types of Soaps:

There are different types of soaps available today for laundry purposes. According to the preparation and quality they are classified into (1) Hard soap and (2) Soft soap.

1. Hard Soaps:

1. Hard soaps are these which cannot be easily rubbed on to the surface to be cleaned.

2. They do not dissolve easily in water and hence do not give free lather.

3. Hard fats like Tallow, Lard, and coconut oil produce hard soap with a firm texture.

4. In hard soap caustic soda is used as alkali.

5. Boiling process is generally used in making hard soaps.

6. In hard soap, Sodium carbonate, Sodium chloride or Sodium Sulphate may be added which can increase the detergent property of soap.

7. Laundry soaps are hard soap.

2. Soft Soaps:

1. Soft soaps dissolve readily in water and give free lather. Because of this quality they are wasted more in use.

2. Soft fats like castor-oil or linseed oil are used for the preparation of soft soaps.

3. Caustic potash is the best alkali for soft soaps.

4. Soft soaps are generally manufactured by cold processes.

5. Some neutral soaps and bathing soaps are soft soaps.

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