Jabir (known as Geber in western history) is mostly known for his contributions to chemistry. He emphasised systematic experimentation, and did much to free alchemy from superstition and turn it into a science. He is credited with the invention of many types of now-basic chemical laboratory equipment, and with the discovery and description of many now-commonplace chemical substances and processes – such as the hydrochloric and nitric acids, distillation, and crystallisation – that have become the foundation of today's chemistry and chemical engineering.
In spite of his leanings toward mysticism (he was considered a Sufi) and superstition, he more clearly recognized and proclaimed the importance of experimentation. "The first essential in chemistry", he declared, "is that you should perform practical work and conduct experiments, for he who performs not practical work nor makes experiments will never attain the least degree of mastery."
Jabir is also credited with the invention and development of several chemical instruments that are still used today, such as the alembic, which made distillation easy, safe, and efficient. By distilling various salts together with sulfuric acid, Jabir discovered hydrochloric acid (from salt) and nitric acid (from saltpeter). By combining the two, he invented aqua regia, one of the few substances that can dissolve gold. Besides its obvious applications to gold extraction and purification, this discovery would fuel the dreams and despair of alchemists for the next thousand years. He is also credited with the discovery of citric acid (the sour component of lemons and other unripe fruits), acetic acid (from vinegar), and tartaric acid (from wine-making residues).
Jabir applied his chemical knowledge to the improvement of many manufacturing processes, such as making steel and other metals, preventing rust, engraving gold, dyeing and waterproofing cloth, tanning leather, and the chemical analysis of pigments and other substances. He developed the use of manganese dioxide in glassmaking, to counteract the green tinge produced by iron — a process that is still used today. He noted that boiling wine released a flammable vapor, thus paving the way to Al-Razi's discovery of ethanol.
The seeds of the modern classification of elements into metals and non-metals could be seen in his chemical nomenclature. He proposed three categories: "spirits" which vaporise on heating, like camphor, arsenic, and ammonium chloride; "metals", like gold, silver, lead, copper, and iron; and "stones" that can be converted into powders. In the Middle Ages, Jabir's treatises on alchemy were translated into Latin and became standard texts for European alchemists. Several technical terms introduced by Jabir, such as alkali, have found their way into various European languages and have become part of scientific vocabulary.
Information taken from http://www.learn-persian.com/english/Hayyan_Jabir.php among others