Slippery And Sour Substances:
In ancient times, the Egyptians and Greeks defined certain substances based upon their taste. Both the Greeks and the Egyptians had discovered that one particular substance was very sour. This became to be known as vinegar.[1] The Greeks used a variety of tests to distinguish compounds. One of these was taste, and they divided substances according to whether they were sour, bitter, salty or sweet. As the Greek influence waned and their knowledge passed on to the Romans, they began to refer to sour substances, such as vinegar or lemon juice, as acids.[2]
The Greeks were also familiar with a different category of substances. They found that some slippery substances were left behind as residue after burning certain materials, like potash, which must have been the first to be discovered and was produced from wood ashes, and lime, which was produced from burning seashells. Ultimately, the Greeks discovered a new category to define substances based upon the property of feeling slippery.[1]
To build on the Greek's definition of sour or slippery, a new terminology was developed to speak about things that felt slippery. From the Arabic word al-qaliy, which means "the ashes", the term alkaline was developed.[1]
The Litmus Definition:
In about 1300, a Spanish scholar, Arnaldus de Villa Nova, began to use something called litmus for studying acids and base.[3] Litmus is a water-soluble mixture of different dyes extracted from lichens.[3]
In 1663, a scientist named Robert Boyle discovered that acids would change the color of litmus. When extracted, this dye is blue in color, but when acid is added, the dye turns red. This was the first, easy test, for acids. As might be expected, bases turned the litmus dye from red to blue, and litmus is still used to this day to detect the relative amounts of acid or base in a solution. Since Boyle's time, however, many more dyes and colored substances have been discovered that also change color when exposed to acids and or bases.[4]