Minerals and Metals in Ancient India v2.c40.s4: Concept of Unit Operations
Minerals and Metals in Ancient India v2.c40.s4
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Concept of Unit Operations
v2.c40.s4.1
The modern terminology ‘unit operation’ means the physcial step(s) which are important pre-requisites towards purification and preparation of materials with or without some chemical change termed as ‘unit process’. Pāṇini’s India was familiar with quite a few unit operation principles.
v2.c40.s4.2
Drava (Pāṇ., 3.3.27) meant melting or something which can be melted. Few more words were also used to denote melting: pralaya (melting, losing shape, dissolution — Pāṇ., 7.3.2), vipātana (melting of loha or copper, sneha or fat — Pāṇ., 7.3.39), etc. Sru meant (for liquid) to flow or gush out (Pāṇ., 7.2.13) and the derivative sruva (6.3.115) an object like a ladle, from which liquid gushes out.
v2.c40.s4.3
The opposite of drava (melting), pralaya (losing shape) and sru (to flow) was reckoned as the phenomenon of a molten object or liquid becoming frozen (śita, 6.1.24-26) or solidified (mur, 6.4.21). From mur was derived mūrtta and mūrti, the phenomenon of assuming shape which is possible only for a solidifying object. Coagulation is the aggregation of dispersed phase in a heterogeneous system not necessarily accompanied by loss of heat, as exemplified in coagulation of the protein matter from milk. This phenomenon of coagulation (śīna — coagulated) was distinguished from the process of being frozen (śīta) on account of cooling (Pāṇ., 6.1.24-26).
v2.c40.s4.4
It was realised in ancient India that preparation of material such as somajuice, surā, gold, copper, etc. often involved separation from impurities or purification. The first two alphabets in ‘pure’, namely pu meant ‘to purify’. The link between the European word and the Sanskritic origin is so obvious. Pūta meant ‘cleaned or purified’ (Pāṇ. 6.2.187), and pāva stood for ‘purifying, clarifying or cleaning’ (Pāṇ., 3.3.28 and 49). The words derived from pāva strongly suggest how a particular kind of purification may take place. Niṣpāva, for example, stands for winnowing as well as a step of purification which involves (ni or) downward movement. We have explained that winnowing does involve differential downward movements of particles of different sizes and densities.
v2.c40.s4.5
Utpāva meant a purification step involving some kind of ascent which is implicit in evaporation (upward escape of water vapour from ghī being purified through heating over fire — Pāṇ., 3.3.49) and distillation (in which the escaping vapour is condensed to yield pure liquid as in the case of alcohol, mercury, etc.). The idea of vapour going over for subsequent condensation was reflected in the word pārāyaṇa (5.1.72). Although Pāṇini did not state ‘distillation’ as one of the meanings of pārāyaṇa (going over), and did not refer to pārā or pārada (mercury, which is purified by distillation), the link between the words is quite obvious.
v2.c40.s4.6
Pāṇini mentioned that the word kṣariti means to flow, break away, glide or to distil (7.2.34). The basic idea was the transport of one component or its migration from another. (Akṣara meant the opposite of removal, i.e., that which is indestructible). Pāṇini categorically mentioned kṣara to mean distillation and kṣaraja to mean a substance produced by distillation (Pāṇ. 6.3.16).
v2.c40.s4.7
Allchin (1979) mentioned India as ‘the ancient home of distillation’. The earliest literary reference related to kṣara, yam . . . na viśvadhakṣaradhyai (Rgveda, 1.63.8) refers to rain-water being discharged by Indra all over the world, and clearly alludes to the later part (condensation) of distillation. Pāṇini referred to a distiller as śauṇḍika (4.3.106), the word alluding to intoxication rather than the distilled product causing it.
v2.c40.s4.8
Apart from distilling alcohol or surā, the ancient Indians of the pre-Christian era most probably distilled mercury and zinc also. In Taxilā certain artefacts unearthed look like distillation outfits. Vermillion (assaying 85 per cent plus mercuric sulphide HgS) found in Taxilā might have been used not only as a pigment but also to produce mercury by distillation. A brass vase assaying 34.34 per cent zinc (Marshall, 1951: 568) could not be obtained by the cementation process; zinc metal for this must have been prepared separately by a distillation process. It is significant that while mercury was later mentioned as rasa, zinc came to be known as rasaka, probably implying the ‘juice’ which is obtained like rasa, by a similar process (of distillation).
v2.c40.s4.9
Certain unit operations, though not practised in the area of minerals and metals, were very useful in terms of food processing. We have indicated that winnowing or nispāva using a winnow or śūrpa was widely practised in the ancient India, starting from the Harappan age, for separating grain from husk. Niṣkoṣaṇa meant extraction in the sense of husking shelling of grains, disembowelling, de-seeding of fruits, etc. (Pāṇ., 5.4.62). Such a technique was used for removing the cortex from agate mineral grains also. Su and āsu meant to press out the juice from materials like soma plant-stem and tendril, and the oil from the vegetable oil-seeds (Pāṇ., 3.1.126; 3.2.103; 7.2.72, etc.). After squeezing the juice out, it was necessary to strain or filter the soma-juice, etc. free from suspended solids. Wire-mesh, fibre-mesh or cloth was used as a filtering medium. Such a step of purification was known as prapavana (Pāṇ., 8.4.34), this word being one more in the series derived from the base pu meaning purification.
Linked texts (2)
- Aṣṭādhyāyī — Pāṇini, Sanskrit
- Ṛgvedasaṃhitā — Sanskrit