History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c12.s1: Table Iii
History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c12.s1
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Table Iii
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| Specimen | Copper | Tin | Antimony | Arsenic | Iron | Nickel | Lead | Sulphur | Oxygen | Remarks | Analyst |
| Copper lump I | 96.67 | — | 0 88 | 0 15 | 0 03 | 1 27 | 0 02 | 0 18 | — | Unaltered | Sana Ullah |
| Copper lump II | 92 49 | 0.37 | trace | 1 30 | 1.51 | 1 06 | trace | 2 26 | 1 01 | Partly oxidized | " |
| Fragment of some implement | 95 80 | — | 0.72 | 0.74 | 0 12 | 0.25 | 1 58 | 0 61 | 0 18 | Unaltered | " |
| Copper chisel | 92 41 | — | 0 10 | 3 42 | 0.59 | 0 15 | 3 28 | 0 05 | — | " | " |
| Bronze button | 88 05 | 8 22 | 2 60 | trace | 0 29 | trace | — | 0 84 | — | " | " |
| Bronze slab | 82 71 | 13.21 | 0 33 | 1 17 | 0 42 | 0 56 | 0.11 | — | 1 49 | Partly oxidized | " |
| Copper object | 94 64 | 0 31 | 0 06 | 0.40 | 0 28 | 0 33 | 0 71 | 0 69 | 2 58 | " | Hamid |
| " | 97 23 | — | — | 0 24 | 0 29 | 0 89 | 0 81 | 0 10 | 0.44 | Slightly oxidized | " |
| Bronze object | 90 18 | 7 66 | 0 43 | — | 0 50 | 0 20 | 0 95 | 0 07 | — | Unaltered | " |
| " | 88.49 | 9 88 | 0 14 | — | 0 10 | 0.30 | 0 22 | 0 06 | 0 81, | Slightly oxidized | " |
| Spear head | 97 66 | — | — | 0 06 | 1 11 | 0 14 | 0 70 | — | — | Unaltered | Sana Ullah |
| Celt | 98 37 | 0 09 | — | 1 40 | 0 02 | 0.10 | 0 11 | — | — | " | " |
| Needle | 92 55 | 1 29 | — | 2 90 | 0 20 | 0 21 | 3 72 | — | — | " | " |
| Dagger | 91 00 | 6 76 | 0 44 | 0 04 | 0 74 | 0 14 | 0.58 | — | — | Completely oxidized | " |
| Chisel | 87 42 | 10 45 | — | 1 10 | 0 34 | 0.17 | 0 52 | — | — | Unaltered | " |
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Technique employed in the Indus Valley metallurgy included both casting and forging In the former process the metal had to be previously melted before being poured into a mould. Pure copper, when cast in a closed mould, becomes spongy due to the bubbles of free oxygen. But the addition of a very small percentage of tin or of arsenic acts as a deoxidizing agent. As most of the copper articles found at the Harappa and Mohenjo-daro sites contain these foreign metals in small amounts, their composition was quite suitable for production by casting But curiously enough the closed mould casting was never used for the production of tools in the Harappan Civilization. Most of the bronze objects were products of casting; some, however, had to be shaped and finished by hammering. This indicates that the Indus Valley metal-smiths were quite familiar with the properties of bronze-that enable it to be forged at a temperature just below redness The analysis of bronze objects reveals an advanced state of knowledge of bronze-making on the part of their makers. Copper and bronze vessels have been found together which supports the assumption that they were in simultaneous use. This was presumably due to the scarcity of tin. Copper alloyed with arsenic was also used at Mohenjo-daro and Harappa, as copper-arsenic alloy is comparable with low grade bronze in hardness. As already stated, this alloy might have resulted accidentally from the use of arsenical copper ores for the extraction of the metal. There are evidences that copper articles, such as axes, were made both by casting and hammering; the edges were usually hammered out after plain blades had been cast.
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Copper was possibly smelted from ores near the mines, the metal being afterwards refined in clay crucibles. A fragment of such a crucible with the slag sticking to the edges has been found at the excavation at Mohenjo-daro. From an examination of the analytical results, given above, of specimens of various articles found at the Indus Valley sites, it may be concluded that the people at that time were acquainted with four distinct varieties of copper and its alloys: viz. (a) crude copper, (*b*) refined copper, (*c*) copper-tin alloy or bronze and (*d*) copper-arsenic and copper-arsenic-lead alloys.
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(*a*) Crude copper, the first product of the smelting furnace, was too rich in sulphur to be worked up by hammering and was suitable only for casting heavy and plain objects.
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(*b*) Refined copper, on account of its purity and ductility, rendered it quite suitable for making vessels of elaborate shapes, as also for obtaining sound casting in closed moulds. The presence of small amounts of arsenic and antimony imparted appreciable hardness to the metal.
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(*c*) The percentage of tin in the bronze articles found at the Indus Valley sites lies between 4.51 to 13.21. Those with 11-13 per cent of tin are more common, although lower grades also occur to some extent. The presence of the high grade alloys well-suited for sharp-edged tools, with a fairly regular proportion of tin, leaves hardly any doubt that the addition of the white metal was intentional and not the result of mere accident. Tin was possibly imported from outside, likely from Persia. It is obvious that this stage in metallurgy had been reached after prolonged experimentation and experience with copper and its alloys with arsenic and tin. An appreciable amount of antimony and arsenic has been found in many bronze articles, which thereby gain an increased hardness.
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(*d*) Copper-arsenic alloy was employed as a substitute for low grade bronze. Presence of lead in copper and bronze tended to increase their fusibility, rendering the latter more suited for casting. But it was more probably an accidental impurity than an intentional addition. Copper ore is unknown in Sind. The nearest deposits are to be found in the countries bordering on the west of the Indus Valley. In Baluchistan rich copper ores occur at Shah Ballaul and at Robat. Here large heaps of copper slags have been found indicating ancient smelting at these sites. Perhaps the ores were mined and smelted here and then transported to the cities of Harappa and Mohenjo-daro. The evidence of the extraction of copper is still to be seen at the various village sites belonging to the Mohenjo-daro Period of history that have been uncovered in Baluchistan Deposits of copper ore also occur at Râs Kuk and the Kojak Amran range in Baluchistan In Afghanistan there are rich veins of copper in Shah Maksud range In Persia there are copper deposits at Anarek and in Kaleh Zeri (Kerman) At both these places there are evidences of extensive ancient workings The nearest copper mines in India proper are those in Rajputana These are situated near Ajmere in Sirohi, in the Mewar and Jaipur states especially those at Khetri and Singhana bear the evidence of having been worked from very early times In the copper lumps found at Mohenjo-daro the small quantities of sulphur indicate the use of the sulphide ore, which abounds in these mines, for the extraction of copper. The presence of lead in some of the copper objects is also noteworthy Copper ores associated with lead occur in Rajputana and in the Hazaribagh district, as also in Afghanistan and Baluchistan. Samples of copper ores from Khetri, Alwar, Singhbhum and Afghanistan contain both nickel and arsenic, while those from Bilaspur and Nellore are entirely free from nickel It can, therefore, be concluded that the Indus Valley copper most likely came from the Indian ores in the Rajputana district and Baluchistan, though Afghanistan and Persian sources are not absolutely ruled out
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It is believed that the furnaces employed for the smelting of copper ores were simply a concave depression in the ground Kilns have not yet been identified with certainty There is evidence that charcoal was used as a fuel The pits were lined with clay. A layer of charcoal was probably first placed on the floor of the pit and ignited Over this the ore and charcoal in alternate layers might have been arranged and the firing maintained by the aid of a blast
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The use of gold was confined to jewellery in the Indus Valley, while silver was used for jewellery and also for ornamental vessels Gold was obtained from South Indian gold fields in Mysore and Madras Silver might have been obtained with gold from the same source or from argentiferous lead of Burma. Articles made of gold-silver alloy, electrum, have also been found at Mohenjo-daro. A sample of silver found at Mohenjo-daro has been found on analysis by Hamid (archæological chemist) to contain
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| Silver | . | 94·52 per cent. |
| Lead | . | 0·42 „ |
| Copper | . | 3.68 „ |
| Insolubles . (silver chloride etc.) | .. | 0.88 „ |
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This seems to indicate that the silver was obtained by smelting argentiferous lead ore associated with cuprite of which the cerussite, found at Baluchistan, might be a probable source. The process of extracting silver from lead was undoubtedly known to the people of the Indus Valley. Silver might have been obtained also from Afghanistan and Persia. From Persia, too, gold may have been obtained and more certainly tin and lead.
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Minerals
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A large number of minerals, ores and rocks were known to, and in use among, the Indus Valley people. These include lapislazuli, turquoise, rock crystal, limestone, soapstone, alabaster, hæmatite, amethyst, slate, agate, jasper, chalcedony onyx, bitumen, steatite, sodalite, jade, lollingite, arsenical pyrites, etc. Most of these were found in the form of beads, pendants, etc. for ornamental purposes, and some like steatite were often coated with a glaze. Lollingite and leucopyrites were also utilized for the preparation of arsenious oxide and arsenic. Cerrusite and cinnabar have also been found at Mohenjodaro. They were probably used for cosmetics and medicinal purposes. White lead was possibly utilized for plasters, eyesalves and hair-washes. Galena was employed for the preparation of eye-salves and paints.
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Bitumen, alabaster and steatite were probably obtained from Baluchistan. Turquoise and lapislazuli are certainly of Persian or Afghan origin. Hæmatite was imported from the islands of the Persian gulf. Agates, carnelians, onyx and chalcedony, as also rock crystal, were obtained from Kathiawar region. Rajputana is most likely to have provided steatite, slate, jasper, chalcedony, etc.