History Of Bleach
The dictionary definition of bleach is "the whiteness that results from removing colour from something." The process of bleaching is now extensively applied in science. It is a process that provides a handy solution to countless industrial activities.We have already learned that bleaching is a process of whitening or divesting objects from their colours. Through the influence of light or sunlight and in the presence of oxygen and moisture, bleaching is a never-ending and continuous process found in nature.This process constitutes as an essential part of treating several articles and commodities in the initial stages. The art of bleaching is typically focused on certain articles, such as textile products. Cotton, linen, silk, wool and other textile fibres are bleached for whitening as an essential step. It is also applied to paper pulp, beeswax and some oils, and other substances, besides wheat flour, petroleum products, oils, fats, straw, hair, feathers and wood.Bleaching is a rather old process. Prehistoric human beings were also familiar with the effect of sun on various substances. In fact, even in primitive times, we can find examples of items being exposed to sunlight for purposes of bleaching. Some of these civilisations were based in Egypt, China, Asia and Europe.The oldest traces can be found in the Egyptian civilisation (around 5000BC). Thus, Egyptians were thought to be experts when it came to applying the whitening power of the sun to bleach objects. They used to discolour their linens by exposing their clothes to sunlight.Bleach was discovered even before the third millennium BC. The people of that time had adequate knowledge about a solution that could be developed from wood ashes, which, after mixing with water, turned into lye (a substance that is obtained by leaching or removing soluble or other components by percolating a liquid). They knew that the resultant liquid would lighten colours.
They also knew that steeping or soaking things in lye would whiten linen to the extent that if it was allowed to remain dipped for a long period of time, it would completely disintegrate linen. The whitening process with this lye method is a bit tricky. Additionally, it is cumbersome because it consumes several hours. Furthermore, it warrants extra care as it is pretty strong.
The Dutch are attributed for the modification they brought about in this sphere in the 11th and 12th century AD. During this time, they emerged as experts on the science of laundering in the entire European community. To soften the harsh effects, they seasoned lye with sour milk. They never let anybody know about their secret and, as a result, the process remained a mystery for many years.
Till the mid-18th century, the Dutch dominated and maintained their supremacy in the bleaching trade. Thus, all brown linen, manufactured at the time principally in Scotland, was shipped to Holland for the purpose of bleaching.
The entire course of action, from its despatch to return was a long process - it took about seven to eight months. To achieve the results identical to that obtained by using lye, they would soak and sun-dry the linen many times. The cumbersome aspect of this was that lye needed up to eight weeks, not to mention the space needed for drying the fabric out in the sun.
Harlem, a city in western Netherlands, an industrial city best known as a flower-growing centre and distribution point for bulbs, especially tulips, was the hub of the bleaching process at the time. Linen was usually soaked in waste lye for almost a week as the first measure; boiling hot potash lye would usually be poured over that in next stage. Afterwards, the cloth was usually drawn out, washed and later on placed on wooden containers, filled with buttermilk. In the vessels, the cloth was allowed to remain dipped for about five to six days. Finally, the cloth was spread on grass, probably in a tenterhook arrangement. During the entire summer, the cloth usually remained exposed to sunshine, while being moist.
This entire course consisted of bucking (steeping or soaking in alkaline lye) and crafting (bleaching on the grass), needed to be repeated alternately five to six times to achieve the required level of whiteness.
In the 16th century, scientists fancied a new chemical to replace sour milk. John Roebuck, in 1746, began using diluted acid instead of sour milk. He used diluted sulphuric acid in place of sour milk. This was a great improvement which resulted in the application of sulphuric acid in the bleaching process owing to which the entire procedure required only 24 hours and often not more than 12 hours. Usually when sour milk was used, six weeks, or even two months, were required, depending on the weather. Consequently, the practice of bleaching was curtailed from eight months to four, which made the trading of linen quite profitable.
In 1774, Swedish chemist Karl Wilhelm Scheele (who is credited with the discovery of oxygen) discovered the chlorine which is a highly irritating, green-yellowish gas and belongs to the to the halogen family. Scheele found that chlorine had the ability to destroy vegetable colours. This discovery motivated French scientist Claude Berthollet to fancy its utility in the bleaching process in 1785.
In experiments carried out during the initial stages, the person involved in it was required to produce chlorine himself. The stuff needed to be bleached was either exposed to the gas in a chamber or steeped in an aqueous solution. Keeping in view the olfactory effects of chlorine and the health risks it posed, this exercise was met with failure in the beginning.
In 1792, in the town of Gavel (in Paris), eau de Gavel (water of Gavel) was produced by combining potash solution (one part) with water (eight parts). However, the greatest momentum to bleaching industry was provided when, in 1799, a chloride of lime was introduced by Charles Tennant from Glasgow, the substance we now know as bleaching powder.
Peroxide bleach was discovered in the middle of last century. Although it takes away stains, it lacks the ability to bleach most coloured fabrics. It is considered to be more user-friendly, as they do not cause weakening of the cloth. It also don't disinfect and can be safely added in laundry detergents. Another distinct feature is that it has a longer shelf life as compared to other types of bleaches It has more popular in Europe where washing machines are produced with inner heating coils which can increase the water temperature right up to boiling point.
Chlorine bleach has disinfecting qualities and is a powerful germicide. It is useful in disinfecting water, especially in areas where contamination is rampant. In New York City's Croton Reservoir, it was initially used to disinfect drinking water in 1895. In recent times, community health activists have promoted bleach as a low-cost method of disinfecting the needles of intravenous drug users.
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