3. THE RAW MATERIALS

Four basic raw materials are involved in the manufacture of soap:

1. oils and fats 2. soda lye or potash lye* 3. brine** (for glycerine recovery) 4. additives: sodium carbonate, sodium silicate, dyes, perfumes, etc., the use of which depends on the quality and type of soap desired.

* Soda lye - aqueous solution of potash soda prepared by dissolution of 30 to 35% by weight of sodium hydroxide (NaOH).

Potash lye - aqueous solution of caustic potash prepared by dissolution of 30 to 35% by weight of potassium hydroxide (KOH).

** Brine - salt water prepared by dissolution of 10 to 20% by weight of sodium chloride (NaCl; sea salt).

The main properties of a soap are its lathering power, detergency, consistency, rate of dissolution in water, and lather stability. These properties depend chiefly on the nature and quality of the fatty materials used and to a lesser extent on the manufacturing process, solidification and cooling method, as well as the refining and finishing stages.

The soap maker's art involves mixing different oils and fats to obtain a soap with the desired properties. To come up with their "formula", the soap maker has 3 types of fatty materials available:

¯ lauric oils	¯ hard fats	¯ soft oils
· coconut oil · palm kernel oil	· tallow (cattle, sheep) · palm oil (stearin)	· soya bean oil · groundnut oil · cotton seed oil

Lauric oils, found in high proportions in coconut oil and palm kernel oil, are the fatty materials with the best combination of the properties generally desired in soap. They are used in the majority of formulations because they provide high lathering power and detergency. They are used in cold or hot saponification, in combination with other oils and fats, to improve hardness and to slow down the rate of dissolution of manufactured soaps.

Tallow and palm oil, usually after bleaching and deodorisation, are the fatty materials most often used in combination with lauric acids.

Soft oils are sometimes used in limited proportions in the manufacture of low-grade soaps because of their poor properties.

Noteworthy among other sources of fatty raw materials are "soapstocks", by-products of edible oil refining which are processed to correct their free acidity. These raw materials are purified and used in combination in the manufacture of low-grade soaps.

Generally speaking, the most common soaps are manufactured by saponification of a combination of lauric oils and hard fats in a ratio of 1/3 - 2/3. However, these proportions are subject to wide variations depending on the type of soap desired - toilet soap or household soap - or the manufacturing method.

Technical constraints are compounded by constraints of an economic nature linked to the cost of the raw materials and the sale price of soap, which are subject to wide fluctuations. Other factors such as the security of supply and the consistent and uniform quality of the raw materials also play their part, which means that the soap maker has very little room for manoeuvre in selecting the oils and fats to be used in soap formulations.

The problem of oil and fat supplies is crucial and often underestimated. Although oleaginous resources generally exist in developing countries, oils and fats for soap manufacture can sometimes be lacking both in quantity and quality, obliging the promoter to import raw materials or add an oil press/mill to the production line. However, for local oil mills, a soap factory may represent a diversification of activities and an upgrading of poorer quality raw materials, following the example of the manufacture of margarines or other oleaginous products.