Shloka: Sodasangulavistirnamhastamatrayatamsamam |
Meaning: The Koshti equipment (furnace) is 16 inches in breadth and is of equal height and length of 1 palm (6 inches). It enhances the strength of ores.
Shloka: Bhandakanthadadhaschidrevenunalamviniksipet |
Meaning: In the opening under the neck of the vessel fit the bamboo tube. Taking two (hemispherical) brass vessel, fill them with water and close them and place the mouth of the tube appropriately and firmly there.
Shloka: Nalikasyamtatrayogyamdrdhamtaccapikarayet |
Yuktadravyairviniksiptahpurvam Tatraghaterasah ||
Yavadusnambhavetsarvabhajanamtavadeva hi |
Jayaterasasandhanam dhekiyantramitritam ||
Meaning: Mercury mixed with proper ingredients is previously poured in the vessel. The mixture heated with fire falls down on the water through tube. As long as the whole vessel is hot, distillation takes place. This is called Dekiyantra.
Source: Rasa-ratna-samuccayah, Adhyayah 9, Slokah 43, 11-14, Vagbhatah (12th Century AD)
Etymology: Koshta + yantram = Enclosed + device = Closed Furnace.
Dhekiyantram and Kosthiyantram were the two setups or procedures used for Distillation in the ancient times. Ancient Indians where much ahead with the art of making metals like zinc and brass. Zinc is not found in its purest form as ore. It is found along with other metals and impurities. For obtaining zinc to its purest form it has to be distilled. The main ore of zinc being calamine or Zinc carbonate is available in nature as heavy crusts. They are usually green, brown or blue due to the impurities in the ore. So, for the purification of this Zinc ore a method called Koshtayantram is used.
A script of ancient India known as Rasarnava has the description of distillation of Zinc using Koshtayantram. Calamine, known as Rasakais, is mixed along with wool, lac, Borex and Terminalia chebulaall and covered in a crucible which harvests the presence of zinc. The above combined mixture is boiled along with clarified butter and milk. This paste is then made into small balls. A pot filled with water is placed below the charcoal holder. The crucible having the mixture of ore is placed in an inverted position above the vessel of water. The essence from the crucible drops into the vessel of water. Zinc from the water is then extracted.
The Dhekiyantra setup has two earthen pots, one filled with distilled liquid mercury and the other has Rough mercury. A bamboo tube is connected between the two pots. The pot with Rough mercury is called Kamasyasamputa. The Rough mercury is heated and then it starts distilling into water through the bamboo tube.
Distillation of Zinc from its ore is achieved by two main procedures namely Zinc smelting and Zinc Processing. Zinc smelting involves two methods namely Pyro metallurgical process and electrolysis process. The zinc ore is roasted or heated at high temperature. In this process over 90% of Zinc from its ore is concentrated. Electrolysis process involves four major steps namely leaching, purification, electrolysis and melting and casting.
Pyrometallurgical process is employed for extraction of mercury from its ore. The sulphide ores are heated in high temperature in the presence of oxygen. The gases are then liberated above boiling point. These vapours are then condensed and metal is extracted from it.