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History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t8: (VI.2) Mercury

History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t8

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(VI.2) Mercury

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The age of introduction of Mercury to the ancient Indians is not demarcated very clearly but it is sure that this metal or its minerals have not been mentioned in the Vedic text. It is also very clear whether sindur used by married Indian women was HgS mineral although this compound has been called Rasa sindur in the Ayurvedic text *Caraka Saṃhitā*. In Sanskrit this metal is called ‘Parada’ or Rasa and Hg as well as HgS have been extensively used in the preparation of Ayurvedic medicines. In *Rasaratna Samuccaya* and other literature on ‘*Rasasastra*’ description of use of Cinnebar (*Hiṅgula*) to produce Mercury (*Hiṅgulakrasta Rasa*) has been described along with the details of the distillation apparatus used for its extraction. HgS gets decomposed very easily on heating in air or with lime to red hot temperature. The reactions are as follows:

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(1) HgS + O₂ —— Hg + SO₂ ..(1)

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(2) 3HgS + 2CaO —— 2CaS + 3Hg + SO₂ ..(2)

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The Ayurvedic literature also describes the process of purification of this metal and its reconversion to HgS for Mercurial preparations. In latter period Hg has found its use also in amalgamation process for the extraction and over laying or coating of Gold and Silver (Gilding) on copper or brass objects as well as for the extraction of Gold from very lean ores. In the Medieval period with the progress of the alchemical processes its use has increased in many other areas such as thermometry etc.

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(VI.3) Arsenic

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It is found in nature mostly as Arsenide (As₂S) and as As₂O₃ which have a very low boiling point. Although the hardening effect of this element on copper was known from antiquity this element in the metallic form was known only in 1694. Earlier Arsenic sulphate found in the copper sulphate ore was probably co-reduced to produce Cu-As alloy which had higher hardness (220 to 230 BHN) as compared to the cold worked copper. This property was well recognised by the copper age people and used to produce hard and sharp edge on copper weapons.

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(VI.4) Antimony

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Antimony sulphate (Stibnite) has been known to the ancient people (4000 B.C.) as black colouring agent, or toiletary for colouring eye brows. It was also being used for the preparation of ‘*Surma*’ an Ayurvedic medicine used for the cure of eye diseases and also as toilet material. Sb₂S₃ readily gets oxidized to Sb₂O₃ at 290 to 500°C and on fast heating it volatilises at 650°C. It can be easily reduced by ‘C’ to produce Sb metal which is also known as ‘Star Metal’ owing to its structure. No mention of this metal has been made in ancient Indian literature nor artifact bearing this metal in recognizable quantity has been obtained during archaeological excavations. In the latter period this metal has been alloyed with lead etc. to develop bearing and typing alloys.

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The discovery of other metals and elements of the periodic table had to wait till the age of alchemic and experimental chemistry in the West. In fact during the 17th to 20th century while the concept of modern chemistry and metals technology were being developed and industrialised, in India the ancient art of metals technology was being lost owing to the religious rituals and concept of secrecy associated with the Indian practices, and it also suffered serious set back due to the political disturbances.

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Alloy Technology

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The chemical analysis of ancient metal artifacts have revealed the presence of many other elements in minute quantities affecting the properties of the parent metal many a times favourably. For example the copper artifacts containing 2-5% Arsenic have been reported to have better hardness than pure copper but it is difficult to say whether this alloy originated from the arsenic bearing complex sulphide ore or Arsenic metal deliberately added to copper to produce this alloy. In exceptional cases copper containing 20-24% Arsenic have been reported and this must have been definitely made by alloying. Most probably the acquaintance with first alloy might have been accidental due to the coexistence and co-reduction of two or more metals but after observing the beneficial effect on strength, hardness, hot and cold workability, lusture and corrosion resistance ancient craftsmen must have started adding these metal deliberately and thus the alloy technology must have been born. The acquaintance with the naturally occurring Au-Ag alloy ‘Electrum’ found at Kolar might have been the first introduction of Indians to the difference between the property of pure Gold and Au-Ag alloy. The history of production technology of alloys most probably begins with the manufacture of bronze or Fe-C alloys of known composition, but it is difficult to say which one of these was developed first because in India according to the Indian Archaeologists bronze and iron have an overlapping growth. Dube and Prakash(1970) have studied the analysis of the ancient Harappan bronze objects and they have concluded that these alloys of Cu+Sn were not a result of chance intermixing but designed to develop certain specific properties. Biswas(1981) has reviewed *Rasa Ratna Samuccaya* and noted that the alloy of two metals were called *Durmela lohadvayametañca* if the additives were incompatible otherwise it was known as *dvandvana*. The process of addition to the liquid metal was known as *Niravapana*, and an alloy containing five metals was called *Pañcaloha* or *Vartaloha*. Many specific alloys have been given a separate name such as brass was called ‘Suvarnaka’ and Cu-Pb alloy *Sulvanage*. The objective of alloying could have been one or more of the following:

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(i) To produce alloys having similar colour and lusture as Gold, for example ‘Suvarnaka’ or brass.

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(ii) Improvement in the physical properties such as strength, hardness etc.

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(iii) Improvement in hot and cold workability.

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(iv) To produce alloys having lower melting point and better castability.

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(v) To produce alloys having capacity to join two metallic components such as solder alloy etc.

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(vi) To produce a cheaper metal and reduce the consumption of precious metal.

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(vii) to produce alloys having specific properties such as zinc alloy used for producing ‘Bidri’ ware.

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(viii) To produce coinage metal of specific composition from security point of view and to prevent production of counterfeit currency.

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(ix) To produce Fe-C alloys of variety of compositions which could be given a variety of thermo-mechanical treatment to develop desired properties in the object.

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The first man made alloy might have been produced by co- reduction of mixed ore minerals such as in the case of production of bronze and brass. The techniques applied for producing some of the important alloys in ancient India are being discussed below.

Cites (2)