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History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c36.s7: Gems

History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c36.s7

Language
English

Gems

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Among the sixty-four branches of arts and sciences recognized in the ancient Kamasutra of Vatsayana* (5th century A D) occur the following: (a) testing of gold and the gems, (b) knowledge of the colouring of gems; as also knowledge of mines and quarries. Varahamihira (6th century A.D) in his Vrihat Samhita, as already stated, conveys much useful informations on the subject, and refers in his turn to experts who preceded him

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The Garudapurana (circa 9th century A.D)* under the heading of *Ratnapariksha* (examination of the gems) devotes several chapters to a detailed and exhaustive description of the gems.

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From time immemorial the gems have been valued in India not only for purely decorative and ornamental purposes, but also as agents for warding off perils and the malignant influences of the planets, and for securing luck and longevity Hence, particular attention is paid to the testing of gems, as their virtue increases in proportion as they are faultless and flawless.

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The typical characters which, according to Garudapurana, are most relied upon for differentiating one species of gem from another are (1) the relative weight, (2) hardness, (3) lustre, transparency and colour, (4) fusibility, specially when heated in combination with alkalies

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1. *Relative Weight.*—The principle of Archimedes being evidently unknown among the Hindus, the measurement of volume could only be roughly approximate Thus it is stated that a stone may be of the same species as, and equal in volume to, a *padmaraga* (oriental ruby), but will differ in weight from the latter. Empirical and arbitrary scales of weight were adopted as standards. A ruby occupying the volume of a *gunja* (*Abrus precatorius*) may be equal in weight to 10, 7 and 3 *gunjas* respectively. In each case the gem which is of greater weight is superior in quality, and the value thereof is enhanced in proportion.

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In the case of precious metals, however, adulteration was detected by an ingenious device, which may be regarded as a near approach to the principle of Archimedes, Thus, for testing the purity of gold the following instruction is given by Garuda. A wire of gold to be tested is drawn through the orifice of a corundum. In a similar manner another wire of the standard gold is drawn through the self-same orifice. As these wires are of equal diameters, equal lengths will have equal weights, provided the sample is pure.

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2 *Hardness* :—The spurious substitute of any precious stone may easily be detected by its difference in hardness and low specific gravity. The suspected gem may also be rubbed on a whetstone; if it simply gains in lustre but does not lose in weight (by abrasion), the specimen is to be regarded as genuine (test of a ruby). Diamond and corundum alone will scratch ruby and sapphire. All the gems occurring in this world, as also the metals, will be scratched by a diamond, but the latter will not be similarly affected by the former. A diamond alone will scratch a diamond.

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3. *Lustre, Transparency, Colour and other Optical Properties* :—Difference in lustre is often regarded as a diagnostic feature of the gems. According to Varaha gems of superior qualities should possess cool (lit. waxy) lustre, be limpid and emit rich rays. Classification according to colour is often enjoined. For instance, a diamond may be perfectly colourless, or it may be yellow, black, red or copper-tinted. Stones which are translucent, opaque and of dull colour are inferior in quality. In the case of diamond special stress is laid on its displaying the colours of the rainbow (due to its high dispersive power). Some gems have only one shade of colour, other again two (dichroism).

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The changes in colour, which the ruby and the sapphire undergo under the influence of heat, had evidently been carefully observed. This test is to be applied with extreme caution, as, in case the proper degree of temperature is exceeded, the stone may be materially injured.

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readily yield sulphuric acid which, with sodium chloride and nitre, might be expected to produce aqua regia.

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*Vida* or *Vit* (now known as *kalanimak* or ‘black salt’):— It is difficult to ascertain what it meant in the Ayurvedic age at the time of the Charaka and the Susruta. An account of the preparation of the black salt is given in Watt’s Dictionary of the Economic Products of India.

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“Black salt is prepared in upper India chiefly at Bhewani in the Hissar district by heating together in a large earthen pot 82 lb. of common salt, one pound of the fruit of *Terminalia chebula*, and one pound of *Phyllanthus emblica*, and one pound of *sajji* (impure carbonate of soda), until by fusion of the salt the ingredients are well mixed; then the pot is removed from the fire and its contents allowed to cool and form a hard cellular mass. This preparation is used medicinally, principally as digestive”

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The salt has a reddish-brown colour and consists mainly of sodium chloride with traces of sodium sulphate, alumina, magnesia, ferric oxide and sulphide of iron. During the fusion, a portion of the sodium sulphate is probably reduced to sulphide by the organic matter (*T. chebula*). This then reacts with the traces of iron salt present to form the sulphide of iron.

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Killing of Metals

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From the time of the Charaka and the Susruta we find metallic preparations in the shape of oxides, sulphides and sometimes chlorides, recommended for internal administration. The various formulas, which will be found scattered throughout above, give us methods for *killing* metals But a *killed* metal is not necessarily a compound; it sometimes means a metal deprived of its well-characterised physical properties, e g. colour, lustre, etc Thus the Ayurvedic *killed* gold and silver often represent the respective metals in a fine state of division. This is illustrated by the following recipe from Rasaratnakara by Nityanathia:

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"Rub gold-leaf with four times its weight of *killed* mercury (i e sulphide of mercury) and sublime the mixture in a closed crucible. On repeating the process eight times, the gold is *killed*."

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As the Hindu Iatrochemists were very particular about the *killing* of the metals being ensured, they had often to hit upon proper tests for securing this purpose Thus Rasaratnakara says:—"In order to examine whether the mercury has been completely reduced to ashes, it has to be heated over a gentle fire for three hours. If the weight remains constant, know then that it has been completely *killed*." In other words, it means that if there be any free mercury present, it would volatilise off and thus there would be a loss in weight.

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According to Hindu alchemists, there are four kinds of the ash (*bhasma*) of mercury; namely black (*kajjali*), red (*vermilion*), white and yellow. The white variety is often spoken of as *rasakarpura* or camphor of mercury; it is often found to be almost pure calomel and sometimes a mixture in indefinite proportions of calomel and corrosive sublimate.

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The chlorides of mercury are found to be medicinally used from the 12th century downwards, and various recipes are given for their preparation. The earliest account seems to occur in Rasarnava (Ch. XI, 24), where we find a mixture, among other drugs, of green vitriol, alum and salt, described as capable of *killing* mercury in an instant (p. 139) A more detailed description is found in Rasendrachintamani, a work which may safely be placed in the 13th-14th century. There the author Dhundhukanatha says: "I am now going to explain the process of preparing *rasakarpura*, which is a remedy for all diseases. Take a strong earthen pot and fill one-fourth of it with common salt and place over it a mixture of brick-dust, alum and rock-salt. Rub mercury with the juice of Indian aloe and an equal weight of the above mixture into a paste, deposit it in the earthen pot and cover it with the same ingredients The pot is to be firmly closed with a well-fitting lid. Now apply heat for three days together."

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Another work of the Iatrochemical Period, Rasendrasarasamgraha, describes the following process for obtaining the *svetabhasma* or white ash. "Rub mercury repeatedly with *pamsu* salt (i.e., *audbhida* salt) and the juice of *Euphorbia neriifolia*: place the mixture inside an iron bottle, the mouth of which is closed with a piece of chalk. The bottle is embedded in a mass of salt, and then fire is urged for an entire day. The white deposit in the neck of the bottle is to be collected."

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The Bhavaprakasa, written about 1500 A.D., prescribes calomel in the treatment of *phirangaroga* (lit. the disease of the Portugese; i.e., syphilis) and gives the following recipe: "Take of purified mercury, *gairika* (red ochre), brick-dust, chalk, alum, rock-salt, earth from ant-hill, *kshari lavana* (impure sulphate of of soda), and *bhandaranjika* or red earth, used in colouring pots, in equal parts; rub together and strain through cloth. Place the mixture in an earthen pot, cover it with another pot, face to face, and lute the two together with layers of clay and cloth. The pots so luted are then placed on fire and heated for four days, after which they are opened, and the white camphor-like deposit in the upper part is collected for use."

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The chemical reactions, involved in the above methods for the preparation of calomel, may be explained as follows: Alum, magnesium sulphate or ferrous sulphate, when heated, yield some sulphuric acid. This reacts with common salt to liberate hydrochloric acid. The latter undergoes aerial oxidation in contact with ferric oxide from the brick dust, *gairika*, clay, etc., acting as a catalyst, and sets free chlorine, which attacks the mercury, giving rise to calomel. Alumina from alum or from clay may also catalyse the reaction to a certain extent like the ferric oxide.

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