History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c40.s5.1

c40.s5.1

The operation of heat is, of course, universally implied in chemical combinations. Where the application of external heat is wanting, Vatsyayana, the great Doctor of the Nyaya, points to the operation of internal heat. In the case of combustion, we have seen, Vijnana-bhikshu explains the heat as latent in the Earth-substance, the fuel, from which it breaks forth. Udayana points out that the solar heat is the source of all the stores of heat required for chemical change in the world. The change of colours in grasses, for example, is due to *tejas*, in the form of latent (invisible) heat, not in the form of *agni* (fire); and the cold in winter cannot take away this store derived from the sun (Udayana,—Kiranavali). Similarly, it is under this solar heat that the unripe mango ripens, *i.e.*, changes colour, taste, smell, etc., showing that there is chemical transformation, or subtile decomposition and recomposition, going on; and this is also the case with the rusting of the metals, which is a combustion due to the solar heat, even as the conversion of food into chyle and of chyle into blood are instances of chemical action due to the internal animal heat. But the kind of contact with heat-corpuscles, in other words, the kind of chemical action which transforms colours, is supposed to differ from that which transforms flavour, and this last from that which produces a change of smell, or tactile quality (Nyayabodhini on Annam Bhatta's Tarkasamgraha). Heat and light rays are supposed to consist of indefinitely small particles, which dart forth or radiate in all directions rectilinearly with a sort of conical dispersion and with inconceivable velocity. They may either (1) penetrate through inter-atomic (or *inter-molecular*) spaces as in cases of conduction of heat, which when applied under the pot boils the water, or fries the paddy where there is no chemical action in the pot, no decomposition and recomposition of its atoms, no change in the molecular collocation; or, as with light rays in cases of translucency or transparency penetrate through the inter-atomic spaces with *parispanda* of the nature of deflection or refraction in the same way as when fluids penetrate through porous bodies; or, (2) these rays or particles may impinge on the atoms and rebound back—which explains reflection, or otherwise be obstructed by the atoms in their path, which would explain degrees of opacity, the casting of shadows, etc., all these operations being also physical, and unattended with decomposition and recomposition or alteration of molecular grouping; or lastly, (3) these rays may strike the atoms in a peculiar way, so as to break up their grouping, may transform the physicochemical characters of the atoms, and may again recombine them, all by means of continual impact with inconceivable velocity, an operation which explains all cases of chemical combination.