ADDITIONAL INCOME TAXES mines that the change in margin was due in part to the tax and in part to the increase in other cost, he shall apportion the change in margin between them. (2) Proof that the taxpayer modified contracts of sale, or adopted a new contract of sale, to reflect the initiation, termina- tion, or change in amount of the Federal excise tax, or at any such time changed the sale price of the article (including the effect of a change in size, package, discount terms, or any other merchandising practice) by substantially the amount of the tax or change therein, or at any time billed the tax as a separate item to any vendee or indicated by any writing that the sale price included the amount of the tax, or contracted to refund any part of the sale price in the event of recovery of the tax or decision of its invalidity; but the taxpayer may establish that such acts were caused by factors other than the tax, or that they do not represent his practice during the period in which the articles in question were sold. (j) As used in this section- (1) The term "Federal excise tax" means a tax or exaction with respect to the sale, lease, manufacture, production, processing, gin- ning, importation, transportation, refining, recovery, or holding for sale or other disposition, of commodities or articles, provided for by any Federal statute, whether valid or invalid, if denominated a "tax" by such statute. A Federal excise tax shall be deemed to have been imposed with respect to an article if it was imposed with respect to (or with respect to the processing of) any commodity or other article, from which such article was processed. (2) The term "date of the termination of the Federal excise tax" means, in the case of a Federal excise tax held invalid by a decision of the Supreme Court, the date of such decision. (3) The term "refund or credit" does not include a refund or credit made in accordance with the provisions and limitations set forth in Title VII of the Revenue Act of 1936, 49 Stat. 1747, or in section 3443 (d). (4) The term "tax adjustment" means a repayment or credit by the taxpayer to his vendee of an amount equal to the Federal excise tax with respect to an article (less reasonable expense to the vendor in connection with the nonpayment or recovery by him of the amount of such tax and in connection with the making of such repayment or credit) if such repayment or credit is made on or before June 1, 1936, or thereafter in the bona fide settlement of a written agreement entered into on or before March 3, 1936. (5) The term "taxpayer" means a person subject to a tax im- posed by this section. (k) All references in this section to the purchase or sale (or to parties to the sale) of articles with respect to which a Federal excise tax was imposed shall be deemed to include the purchase or sale (or parties to the sale) of services with respect to which a Fed- eral excise tax was imposed, and for the purposes of subsection (a) the extent to which the taxpayer shifted to others the burden of such Federal excise tax with respect to such services shall be pre- sumed to be an amount computed as follows: From the selling price of the services there shall be deducted the average price received by the taxpayer for performing similar services during the six tax- able years preceding the initial imposition of the Federal excise tax in question. The balance (to the extent that it does not exceed the amount of such Federal excise tax with respect to such services minus any payments or credits with respect to the services made to purchasers as specified in subsection (f) (3)) shall be the extent to which the taxpayer shifted the burden of such Federal excise tax to others. If during any part of such six-year period the taxpayer 115
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