Place of sale determination: contract timing and appropriation fix the State for classifying inter state sales. Section 4 determines the place of a sale or purchase by deeming a transaction to occur inside a State (and therefore outside other States) where: for specific or ascertained goods the contract is made while the goods are within that State; and for unascertained or future goods the goods are appropriated to the contract by seller or buyer, with a single contract covering goods at multiple places treated as separate contracts for each place.