Acids, bases and salts are three distinct classes in which almost all the organic and inorganic compounds are classified. A famous Muslim Chemist Jabir Bin Hayan prepared nitric acid , hydrochloric acid (HCl) and sulphuric acid . In 1787, Lavoisier named binary compounds of oxygen such as and as acids which on dissolution in water gave acidic solutions. Later on in 1815, Sir Humphrey Davy discovered that there are certain acids which are without oxygen, e.g., HCl. Davy proved the presence of hydrogen as the main constituent of all acids. It was also discovered that all water soluble metallic oxides turn red litmus blue, which is a characteristics of bases. The word acid is derived from the Latin word 'Acidus' meaning sour. The first acid known to man was acetic acid, i.e., in the form of vinegar.