S. 36(1)(iii) : Interest on borrowed capital-Presumption that investment was made from interest-free funds-Disallowance of interest is held to be not justified-Expansion and Extension of business-Proviso to Section 36(1)(iii) applies only to extension of business-Proviso does not have retrospective operation-Res judicata is not applicable to income tax proceedings but principle of consistency must be followed.