Acids and Alkalis (Kshara) – The Chemistry of Balance

The Concept In chemistry, acids and bases (alkalis) are analogous to yin and yang. They react to make each other neutral. Kshara (alkali) is a caustic chemical derived from plant’s ash.

The Story Six thousand years before the modern pH scale, the Sushruta Samhita provided a masterclass in chemical reactivity. Sushruta described how to drain the ashes of specific trees and mix them with limestone to create Kshara (caustic alkali), which surgeons used for cauterization. They even understood the concept of neutralization, using acidic fruit juices to stop the “burn” of an alkali if it touched the skin. This ancient method of leaching wood ash is the direct ancestor of the word “Pot-Ash” (Potassium), proving that the foundation of our soap and fertilizer industries began in an Indian surgical hall.

The Timeline

The Original Text

Sanskrit Shloka: ततो यथोक्तानां काष्ठानां राशीन् कृत्वा… दीपयेत् । ततो अग्नौ उपशान्ते… भस्म द्रोणम् आदाय… ॥

Transliteration: Tato yathoktānāṃ kāṣṭhānāṃ rāśīn kṛtvā… dīpayet | Tato agnau upaśānte… bhasma droṇam ādāya… || Sushruta Samhita (Sutra Sthana 11) (Preparation of mild, medium, and strong alkali) .

Meaning: “Then, pile up the wood mentioned… and set it on fire. When the fire is extinguished… collect the ash (Bhasma) in a Drona measure (and dissolve in water).”

 

Related Innovations Long before European chemistry, the Rasaratnakara (c. 7th century CE) documented methods for distilling mineral acids (Vida) capable of dissolving metals. The Sushruta Samhita employed chemical neutralisation to propose acidic fruit liquids to combat the corrosive effects of alkali burns.

Fun Fact The word ‘Ash’ is the origin of ‘Pot-Ash’ (Potassium), which is based on an old method of leaching wood ash that Sushruta described.

The Modern Legacy Alkalis are used in a variety of applications, ranging from soap manufacture to stomach acid neutralisation.