(b) the whole or any part of the additional duties of excise leviable 4[ under the Indian Tariff Act, 1934 , (32 of 1934 .) to the extent to which such duties have become leviable by reason of this Act, as on addition to the contract price payable by him in respect of the goods so purchased. Explanation.- In this section," purchaser" shall not include any person in principal charge of the distribution in India of any of the goods referred to in 3[ section 3.