Oils were also used and if these were boiled with lye, or alkali solution, a soap would have been formed, as is mentioned by the Ebers papyrus of 1550 BC. There is, however, no clear reference to soap and its use by the ancients must remain conjectural. In Graeco-Roman times, oil was much used and also abrasive detergents such as ashes or pumice stone. Soap, it would seem, still was not used, although the roots of certain plants contained saponin and would therefore form a lather.
The earliest clear reference to soap occurs in writings of the first century AD. The word itself is probably of Teutonic or possibly Tartar origin; the latter may, indeed, have invented it. Soap was certainly widely used in mediaeval times, for washing clothes rather than people. The lye was ‘sharpened’ by adding lime (this would convert it to the caustic form) and the clear solution boiled with oil or fat. Lye prepared from wood ashes (potash) yielded soft soap, while that from natron, barilla or rocchetta, forming soda, produced hard soap. A French manuscript of c. 800 has the first European mention of soap.
In northern countries it was soft soap that was produced, by boiling wood ash lye with animal fats or fish oils. Its smell would not have been pleasant, which explains why it was used for washing clothes and not people. But in Mediterranean regions, the ash of the soda-plant was used, with olive oil, to give a hard, white, odourless soap. Its manufacture flourished in Spain from the twelfth century—Castile soap has an eight-hundred-year history. Marseilles became a leading centre in the fourteenth century and later Venice. From these areas, hard soap was exported all over Europe as a luxury item.
In England, by the end of the twelfth century, Bristol had become the main centre for the making of soft soap. Three hundred years later, this had become a major industry, for which ash had to be imported to supplement local sources, to meet the needs of the flourishing woollen cloth industry. The Royal Society, founded in 1662, took an interest in soap manufacture, among many other technical processes, and soon afterwards occurs the first mention of ‘salting out’, that is, the addition of salt to the hot soap liquor to throw the soap out of solution, on which it floats and solidifies on cooling. It can then easily be removed. This had the effect of speeding up the whole process. The imposition of the salt tax hindered the spread of this improvement but its removal early in the nineteenth century was a fillip to this and other branches of the chemical industry.
Soap reigned supreme in the nineteenth century, but it had its drawbacks. It broke down, and so was ineffective in acid, but the main problem was the scum formed on textile fabrics in hard water. The textile industry had a definite need for non-soapy substances with soap-like properties. Again, it was the academic chemists, in Germany, Belgium and Britain over the period 1886 to 1914, who showed the way, by finding that compounds with a long hydrocarbon chain ending in a sulphonate group could act as detergents without the undesirable properties of soap. Industry then had the task of converting these findings into commercially viable production.
The first synthetic detergent appeared in Germany in 1917, stimulated by the extreme shortage of animal fats during the war, and was marketed under the name Nekal, but it was not altogether satisfactory. Further work during the 1920s on sulphated fatty alcohols led at last to a product that was commercially successful for wool, but less so for cotton. During the 1930s American, German and other European chemists developed new detergents incorporating complex phosphates with the previous constituents. Another major development of the 1930s was the production of detergents from petroleumbased materials, in which the oil companies figured.
Another innovation, generally adopted after 1945, was the use in minute quantities of fluorescent whitening agents—‘blue whiteners’ as they are known. Krais, a German chemist, noted in 1929 that certain substances converted the ultra-violet rays in sunlight to visible blue rays. The first patents were taken out by IG Farbenindustrie in 1941 and led to the commercial use of this means of offsetting the yellowing of whites in the wash. Shortage of the raw materials for soap-making during the Second World War hastened the steady replacement of soap by detergents; now soap is almost entirely restricted to personal washing.
Organic Elements and Chemical Challenges
